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Copyright
Journal of Experimental Psychology: General
1982. Vol. I I l. No. 2, 176-207
1982 by thc Amcrican
Psychological Assaiation, Inc.
0096-3445 /82 I llO2-01 76$00.75
Skilled Performance:Effectsof
Adult Age and Experienceon ElementaryProcesses
Timothy A. Salthouseand BenjaminL. Somberg
University of Missouri-Columbia
SUMMARY
Despite a general neglect in contemporary research of the role of practice on the
performance of simple components of skill, considerable evidence indicates that experience leads to substantial improvement in detection, discrimination, ani speeded
classification. One goal of the present research was to identify the mechanisms responsible for practice-related improvement in such elementary tasks. A second goal
was to determine whether there are adult age differencesin the magnitude of practicerelated improvement on simple perceptual and cognitive skills or in the mechanisms
used to achieve that improvement.
Eight young adults (ages 19 to 27 years) and 8 older adults (ages 62 to 73 years)
performed four simple tasks for 5l experimental sessions.On several sessionsthe
subjectsreceivedqualitatively or quantitatively different stimuli to determine the mechanisms responsible for improvement. A concurrent reaction-time task was also performed at three different periods to assessthe level of residual capacity after various
amounts of practice.
The results were interpreted as suggesting that improvement is due to shifts in the
type of information being processed,in the identity or sequenceof processingoperations,
and in the attention requirements of the task. A model incorporating these mechanisms
is proposed and its application to the data is discussed.
Age differencespersistedon nearly every performance measure throughout all levels
of practice. Moreover, there was little evidence that young and old subjects were
qualitatively different in the manner in which they performed the tasks. It is suggested
that the major difference between young and old adults on simple perceptual and
cognitive tasks is the rate of processing nearly all types of information.
of
Skill generallyrefersto the possession
expertisein somefairly complex,temporally
interrelatedbehavior.For example,a skilled
typist or pianist has a well coordinatedsequenceof manual keystrokes;the development of that coordinationis probably the
major part of skill acquisitionin thesedomains, becausethe keystrokesthemselves
are extremelysimplein isolation.However,
in other areasof skill it is possiblethat performance of each individual component
changeswith increasingexpertise.Perhaps
do not occurin the
substantialimprovements
quality of a simplekeystroke,but other perceptualor motoric aspectsof skill might improveindependent
of the overallcoordinated
integrationof the components.
Considerthe caseof drivine an automo-
bile. Driving involvesa complexcoordinated
sequence
of perceptualand motor activities,
and the skilled driver almost certainly possessesa more efficient integration and coordinationof theseactivitiesthan the novice
driver.The expertis probablybetter able to
turn the steeringwheelwhile applyingpressure to the brake or accelerator,to engage
the clutch with his or her foot while manually shifting gears,to soundthe horn while
applyingpressureto the brakes,and so on.
One could also ask. however,if the more
elementaryaspectsof driving also exhibit
differencesas a function of experience.For
example,doesthe skilleddriver havea faster
reactiontime to movethe foot from the acceleratorto the brake? Is there a quicker
perceptionof objects seen in the rearview
176
r77
TIMOTHY A. SALTHOUSE AND BENJAMIN L. SOMBERG
mirror? And is there more rapid apprehension of both speedand mileageinformation
from a singleglanceat the speedometer?
In the current project several discrete
taskswere combinedinto a complexgame,
and the effectsof extensivepractice(50 hr.)
on performanceof each game component
were examined.The tasks were similar to
many of thosecurrently investigatedin cognitive psychology,but weremodifiedslightly
to makethe gamecontextrealistic.The following specificissueswerestudied:(a) Does
experiencelead to improvementsin very elementaryprocesses
suchas signaldetection,
reactiontime, and visualdiscrimination?(b)
If performancedoes improve, what is responsiblefor the improvement? (c) Are
thereadult agedifferencesin the magnitude
or nature of the improvements?
also 1969).The morerecentevidenceon this
topic is also generally consistentwith the
conclusionthat practice greatly facilitates
perceptualperformance.For example,practice-related improvementshave been reported in such tasks as visual acuity (e.g.,
Johnson & Leibowitz, 1979; McKee &
Westheimer, 1978), pitch discrimination
(e.9., Averbach, l97l1. Hartman, 1954;
Heller & Averbach, 1972), auditory sequenceidentification(e.9.,Gengel& Hirsh,
1970;Neisser& Hirst, 1974;Nickerson&
Freeman,1974),visual letter identification
(e.g.,Carr, Lehmkuhle,Kottas,Astor-Stetson,& Arnold, 1976),visualsignaldetection
(e.g.,Colquhoun& Edwards,1970;Taylor,
1964),auditory signal detection(e.g., Kerkhof, van der Schaaf, & Korving, 1980),
speechdiscrimination(e.g.,Samuel,1977),
dichotic listening(Ostry, Moray, & Marks,
1976;Underwood,1974),visual backward
Improvementin Simple Tasks
(e.9.,Schiller,1965;
maskingsusceptibility
A generalassumptionimplicit in much of Ward & Ross, 1977), auditory backward
the literatureon skilled performanceis that maskingsusceptibility(e.g., Loeb & Holdsimpletasksare immune to practiceeffects ing, 1975), and absolutejudgments(e.9.,
and are relatively pure assessments
of ca- Eriksen,1958;Fulgosi& Bartolovic,l97l;
pacity. As Ream (1922) long ago argued, Weber, Green, & Luce. 1977\.
Some indication of the potential magnihowever,the logic might well be reversed:
tude of thesepracticeeffectsis availablein
The effect of practice is very important in considering
a comparisonof the performanceof expejust what the test measures. If the ability required in
rienced and naive subjectsin a study by
test
is
the
fundamental rather than accessory,learning
Nickersonand Freeman(1974).Naive subwill play a very small part and there will be very little
improvement with practice. .
jects in this studywerefound to be relatively
. No improvement would
indicate that a basic.
. capacity is being investigated.
accurate at identifying sequencesof four
(p.308)
tones when the tones were presentedat a
Although one might suspect, on the basis rate of 5 per sec,but a highly practicedsubof the relative neglect of practice variables ject was found to be capableof performing
in many experimental studies, that practice with comparablehigh accuracy when the
or experience has little or no effect on per- tones were presentedat a rate of 500 per
ceptual performance, the evidence to the sec-100 times faster than the rate for the
contrary is overwhelming. As long ago as naive subjects!
A reasonableconclusionfrom thesestud1953, Gibson was able to locate 2l I exper"rule of thumb
imental studies concerned with the effects iesis that the psychophysical
judgments,
of practice on perceptual
many that underordinary experimentalconditions
of which clearly indicated that performance the effectsof practice are limited to a few
did improve with practice (Gibson, 1953,see minutesduring Ithe subject's]first acquaintancewith his task" (Swets& Sewall,1963,
p. 120) is grossly misleading.Neisser and
This research was supported by National Institute on
Hirst (1974) seemto have statedthe case
Aging Grant AG 00694 0lAl awarded to the senior
more accuratelyby suggestingthat "results
author.
obtainedwith naive subjectscannot safely
Requests for reprints should be sent to T. Salthouse,
be generalized to sophisticated ones"
Department of Psychology, University of Missouri, Co(p. 3e8).
lumbia, Missouri 6521l.
Ttc hlcrature conoern
of preorcc on motor tas
tco$rr and consistent-Sr
mcnts haYcbccn docume
Int tn complexitl.from6
Provins.1958:Ream. lt
ball balancing(e.g..Sr.if
turning (e.g..Provins.l9
(c.9.. Brvan & Hartcr. I
Fruchter.I 96O).tracking
& Mote. 1956)and rtt
& Longman,1965:Lcon
19ff). Moreover.virtua
pcrimcntshavedemonst
trmc is greatlyreduccdas
trcc.and in many of thc
becnreportedrhar the inir
conditions
exhibitthegrca
with practice.As a conso
ferential improvementI
manv of the phenomcna
I
damentalcharacteristic
mance are altered at lq
and possibly qualitative
practice.For example,ma
thc magnitudeof the phc
tcnsivepracticc have bcc
stimulus-responsc
compa
Brebner.1973;Fitts & *
ard & Newman,1965)
fractory period tasks (c.g
Stclmach.l97l). and Sr
tasks (e.g., Reisberg,Br
l9t0: Shor. Hatch, Huds
Shaffer. 1972; g116sp.1
becn rcported that subjcc
rial to a parallel mode of
ccssingwith prolongedpr
rad. 1962; Corcoran. 196
& Treisman,196l: Gril
1970;Mowbray & Rhoad
1963,1974: Neisser,Noyk
Shurtleff & Marsetta. l9(
perimentssuggestthat altl
the functionrelatingreacti
of stimulus information
with practice,it is still gn
indicatingthartrue parallc
in effect (e.g., Briggs & I
rows& Murdock.1969:D
boi. l97l: Kristofferrcn
1972c, I 977: Kristofferso
tofferson. 1973: Nickers
SKILLED PERFORMANCE
178
The literature concernedwith the effects 1979;Ross, 1970;Seibel,1963;Yonas &
of practiceon motor tasks is also quite ex- Pittenger, 19'13).
tensiveand consistent.SubstantialimproveThe important point to be noted from
mentshavebeendocumentedin tasksrans- theseresultsis that extensivepracticedoes
ing in complexityfrom finger tapping (e.J., havesubstantialeffectson a varietyof motor
Provins,1958;Ream, 1922;Wells, 1908), tasks,just as it was demonstratedto influball balancing(e.9.,Swift, 1903),and crank enceperceptualtasks.Motivated repetition
turning (e.g.,Provins,1956),to telegraphy of a task may not lead to a qualitativelydif(e.g.,Bryan & Harter, 1897;Fleishman& ferenttype of performing,but it surelyleads
Fruchter,1960),tracking(e.g.,Archer,Kent, to a quantitativelymore efficientand effec& Mote, 1956) and typing (e.g., Conrad tive modeof performancefor many percep& Longman, 1965; Leonard & Carpenter, tual and motor tasks.The implicit assump1964). Moreover,virtually all relevant ex- tion in many earlier studies that basic
perimentshave demonstratedthat response performancecapacitieswerebeingmeasured
time is greatlyreducedasa functionof prac- under conditionsof very limited practiceis
tice, and in many of the studiesit has also thereforealmost certainly incorrect.
beenreportedthat the initially mostdifticult
From the perspectiveof ecologicalvalidconditionsexhibitthe greatestimprovements ity, the investigationof practiced perforwith practice.As a consequence
of this dif- mancewould seemto be necessaryif one's
ferential improvement across conditions, resultsare to havemuch practicalrelevance.
many of the phenomenathought to be fun- Most daily activities are performed with
damental characteristicsof human perfor- many (perhapsthousands)of hoursof pracmance are altered at least quantitatively, tice, and without adequatedata it is imposand possibly qualitatively, with extensive sible to know whetherthe findingsobtained
practice.For example,markedreductionsin from studieswith only a few minutesof practhe magnitudeof the phenomenonwith ex- tice are even addressingthe same types of
tensivepracticehave beendemonstratedin phenomenaas thoseencounteredin normal
stimulus-response
compatibility tasks (e.g., (i.e.,nonlaboratory)
situations.
Brebner,1973;Fitts & Seeger,1953;Leonard & Newman, 1965), psychologicalrefractory period tasks (e.g., Gottsdanker& ll/hat Improves?
Stelmach, l97 l), and Stroop interference
One possiblereasonfor the reluctanceto
tasks (e.g., Reisberg,Baron, & Kemler, acceptthe existenceof substantialpractice
1980;Shor, Hatch, Hudson,Landrigan,& effectsin very elementarytasksmight be an
Shaffer, 1972; Stroop, 1935). It has also inability to specifyhow performancecould
beenreportedthat subjectsshift from a se- be improving in a simple task. What is it
rial to a parallel mode of information pro- that could be learnedin a signal detection
cessingwith prolongedpractice (e.g., Con- task,for example,that leadsto dramaticimrad, 19621'Corcoran, 1967; Davis, Moray, provementsin performance?To state that
& Treisman,l96l; Grill, l97l; Marcel, the individuals,or the processes
usedby the
1970;Mowbray & Rhoades,1959;Neisser, individuals,becomemore proficientor effi1963,1974; Neisser,Novick, & Lazar, 1963: cient is merelyto describethe phenomenon;
Shurtleff& Marsetta,1968),but other ex- an explanationrequiressomespecificmechperimentssuggestthat althoughthe slopeof anism that is altered as a function of expethe function relating reactiontime to amount rience and that is responsiblefor the inof stimulus information is much reduced creasedefficiencyor proficiency.Moreover,
with practice,it is still greaterthan zero- sincethe concernhere is with practice exindicatingthat true parallelprocessing
is not tending over many sessions,such transient
in effect(e.g.,Briggs & Blaha, 1969;Bur- factorsas generaltask unfamiliarity and sitrows& Murdock,1969;Dumas,1972:Gra- uation anxiety are probably relatively unboi, 197l; Kristofferson
, 1972a, 1972b, important.
1972c,1977;Kristofferson,Groen, & KrisThere appear to be at least three broad
tofferson, 1973; Nickerson, 1966: Prinz, categoriesinto which speculations
about the
t79
TIMOTHY A. SALTHOUSE AND BENJAMIN L. SOMBERG
natureof improvementin simpletasksmight the information is subjected,or in the sebe grouped.For the purposeof description quenceof theseprocesses
or operations.For
theseclassesof explanationwill be consid- example,it might be argued that someineredasthoughthey weremutually exclusive, formation-processing
stagescould be omitbut it is likely that two or more mechanisms ted after extensivepractice,or that separate
typically contribute to practice-relatedim- operationscould be performed in parallel,
provementsin many tasks.
rather than serially,after sufficientamounts
The first class of explanationmaintains of experience.
The distinguishingcharacterthat improvementresultsbecauseof a change istic of this classof explanationis that exin the type of information being processed. perienceis assumedto producea shift in the
The qualitativeshift in the natureof the in- nature of the processing,regardlessof the
formationmay be a consequence
of (a) more rate of processingor type of information
efficient figure-ground separationof rele- being processed.
vant from irrelevant information; (b) perAn exampleof an interpretationbasedon
ceptual tuning or sensitizationto specific a changein the type of processingcarried
stimulus features;(c) perceptualcategori- out is Neisser's(e.g., 1967)explanationof
zation based on the experiencehistory or his visual searchresults.In severalstudies
physical characteristicsof the stimuli; (d) Neisserand his colleaguesfound that after
perceptual coding into higher-order units moderateexperiencesubjectscould search
analogousto words or phrasesrather than for the presenceof any of l0 targetsas rapsingle letters; or (e) a shift from one mo- idly as for a singletarget.The interpretation
dality of input to another,as when a typist suggested
by Neisserwas that after practice
shifts from monitoring visual to monitoring the featureanalyzersrelevantfor all targets
kinestheticinformation.Specificalternatives could be examinedin parallel, rather than
within this classthus differ in the meansby serially as was necessaryat early stagesof
which a changein the type of information practice.
A third classof explanationis comprised
occurs,but they can be groupedtogetheron
the basis of a common assumptionthat a of thoseinterpretationssuggestingthat exprimary factor responsiblefor experience- periencewith a task reducesthe attention
relatedimprovementis a qualitativeshift in requirementsof that task. Initially, the task
the type of informationbeing processed.
demands might exceed the available reA specificexampleof a shift in the nature sourcesof attention or consciousness.
but
of information being processedcomesfrom with practicesomeof the processes
required
an analysisof Morse codelearningdata re- for the task may become"automatic" and
ported by Shepard(1963). By examining occur without necessityof deliberateconpreviouslyreporteddata on Morse Codelet- sciouscontrol or attention. The automatic
ter confusionsat differentstagesof practice, processes
may be faster or less susceptible
Shepardwas able to identify a trend for er- to distraction than processesunder attenrors early in practice based on reflection tional control, or they may simply allow
(e.g.,dash-dot-dotsubstitutedfor dot-dot- more of the attentionalresourcesto be condash) and complementation(e.g., dash- centratedon the most difficult operationsin
dash-dotsubstitutedfor dot-dot-dash),and the task.lt is alsopossiblethat the allocation
for errorslate in practicebasedon the num- policies by which attention or conscious
ber of elements(e.g.,dot-dot-dot-dashsub- monitoring is directed toward specificprostituted for dot-dot-dash). An implication cessesbecomemore efficientwith practice,
of this finding is that experienceled to the suchthat only the mostimportantoperations
developmentof a systemof codingand clas- receiveattentionafter moderateamountsof
sifying signalsthat resultedin a changein experience.
In either case,it is assumedthat
the nature of the informationbeing usedat residualresourcesof attentionor consciousdifferent levelsof experience.
nessbecomemoreplentiful as a consequence
A secondclass of explanationcontends of experiencewith a task, and that this inthat experienceleadsto a changein either creasein resourcessomehowleads to imthe specificprocesses
or operationsto which provedtask performance.
Rcscarchon thc relati
ctssing resourccsand p
reccnt: thc relcvant stu
in thc Discussionscctio
this type are already-pop
warrantedcommentin
as the following sclccri
The amount of attentioo n
pcnds on how praaiccd rher
proccss has bccn pracriccd thc
and thcrc is spcculation rhar h
rcquire no attcntion at all. (A
Hos do 1ou train sorncoc
propcr act|ons. cvcn rh6s 16 ;
orcnraln an!onc trho pcrforn
all actrons bccomc autometc.{
srblc rcsponscslo anv situlttd
lhs rar. a minimum of attct
trrnc of dangcr. thc appropn:tc
aut,xnatrcalll.( Norman, 1976
Obviouslr'. quite com;
rmprovement could be g
binations of different m
rt mighr even bc argucd
one crplanatorl mecha
bccausc a changc in on
tlpc of information bei
almosr inevitably lead t<
mcchanisms(e.9.. the n
formation is proccsscd).
sophisticarcdhybrid mod
recanth' propced b1' Sct
I l9?n: Shiffrin & Schn
argued that consistentcr1
lcads to a change in thc r
formcd (a shift from "co
"automatic
dctection" ).
in the amount of procc
quircd to pcrform the t
matic detection is presum
demands on short-term r
capacit.t-.However, thcsc
mentioned that man!' mo
predicting a given scr o
sequently thcy offer guiri
among alternative modcl
A proper evaluatroo of nrdcb
t6ts: ( a ) Can tbc nrodcl pfcdrr
. It
rn diffcring paradigms
rcsults from a singlc rrs
of I
Fcts. a s.n6 in rhrch rocr of t
r anablcs arc maniprletcd' t Shl
o l-a)
SKILLED PERFORMANCE
Researchon the relationshipbetweenprocessingresourcesand practice is relatively
recent: the relevant studiesare mentioned
in the Discussionsection.Interpretationsof
this type are alreadypopularenoughto have
warrantedcommentin textbooks,however,
as the following selectionsindicate:
The amount of attention required by a processdepends on how practiced that processis. The more a
processhas beenpracticedthe lessattention it requires,
and there is speculationthat highly practicedprocesses
requireno attentionat all. (Anderson,1980,p. 30)
How do you train someoneso they will perform the
proper actions,even when in panic? The solution is to
overtrainanyonewho performsdangeroustasks.Make
all actions becomeautomated.Practice the set of posto any situationover and over again.In
sibleresponses
this way, a minimum of attentionis required,and in
get performed
time of danger,the appropriatesequences
automatically.(Norman, 1976,p. 66)
Obviously,quite complexmodelsof skill
improvementcould be postulatedwith combinationsof different mechanisms.In fact,
it might evenbe argued that pure casesof
one explanatory mechanismseldom exist,
becausea changein one mechanism(e.g.,
type of information being processed)will
almost inevitably lead to a changein other
(e.g.,the mannerin which inmechanisms
formation is processed).An example of a
sophisticated
hybrid modelof this type is one
recentlyproposedby Schneiderand Shiffrin
(1977; Shiffrin & Schneider,1977). They
with a task
arguedthat consistentexperience
leadsto a changein the way the task is performed (a shift from "controlled search"to
"automatic detection"), and to a reduction
in the amount of processingresourcesrequired to perform the task-that is, automatic detectionis presumedto occurwithout
demandson short-termmemory (attention)
capacity.However,thesesameauthorsalso
mentionedthat many modelsare capableof
predicting a given set of results, and consequentlythey offer guidelinesfor deciding
among alternativemodels:
A proper evaluation of models should incorporate two
tests:(a) Can the model predict a wide variety of results
in differing paradigms. . . ? (b) Can the model predict
results from a single series of studies on the same sub.;ects.a seriesin which most of the commonly examined
variablesare manipulated? (Shiffrin & Schneider, 1977,
p t't7)
180
The presentstudy, in which the samesubjects performed four different tasks for an
extendedperiodof time, wasdesignedto satisfy the Shiffrin and Schneiderguidelinesin
allowingan evaluationof alternativemodels
of skill improvement.
Adult Age Dffirences in Improvement
Over the past two or three decades,many
experimentalstudieshave been reportedin
which agedifferencesin perceptualand cognitive performancehave been investigated,
and most have shared two characteristics:
(a) They have demonstratedthat older
adultsperformlessaccuratelyor lessrapidly
than young adults on some perceptualor
motor task. (b) The experimentalsituations
have involved inexperiencedsubjects performing for a very limited period of time.
The invariable combination of these two
led Murrell (1973) to suggest
characteristics
the following:
What has been overlooked is that this kind of investigation is confounded by a practice effect and the results,
if they have any applicability at all, can be applied only
to unpractised or inexperienced subjects. (p. 93)
Even more explicit in an earlier sourse,
Murrell (1965) stated,
Anyone reading the results of the laboratory experiments could be forgiven for imagining that any person
who achieves the age of fifty will have become a slow,
forgetful, half-blind, half-deaf, palsied character of little
use in industry. In fact, many older men and women
hold down jobs with complete satisfaction to their employer. This does not mean that the experimental findings are fallacious. The apparent anomaly seems to derive from the use in the laboratory of subjects who are
naive in the practice of the particular faculty which is
49)
being tested. $.
Clearly, Murrell is calling for research
into the effectsof practice on agedifferences
in perceptual-motorperformance.The implicationis that many of the age differences
reported in experimentalstudiesmight be
causedby suchfactorsastask unfamiliarity,
low motivation,high anxiety, or the use of
suboptimal performancestrategies,all of
which could be eliminatedwith experience.
Unfortunately, very little researchhas addressedthis issue,and much of what does
existhaseitherusedonly minimal(e.g.,less
(e.g.,Bothan I hr.) amountsof experience
l8l
TIMOTHY A. SALTHOUSE AND BENJAMIN L. SOMBERG
twinick & Shock, 1952: Botwinick & periencewith a task and age differencesin
Thompson,1967; Grant, Storandt, & Bo- performanceon that task is important for
twinick, 1978; Hoyer, Labouvie, & Baltes, both practical and theoreticalreasons.The
1973:Thomas,Fozard, & Waugh, 1977), practical significancederivesfrom the need
workersof dif- to determinewhetherperformancein shortor hascomparedexperienced
ferent ages,resulting in the possiblecon- term testingsituationsis an accuratereflecfoundingof important selectionfactorswith tion of what can be expectedafter an indithe age comparison(e.g., Murrell & Ed- vidual hasmasteredthe fundamentalsof the
wards, 1963; Murrell & Forsaith, 1960; task. Testsdesignedto measurean individMurrell & Humphries, 1978; Murrell, ual's maximum capabilitiesmay be completely invalid if moderate amounts of
Powesland,& Forsaith, 1962).
Three studies with approximately 5-10 practice result in substantial changes in
hrs. of practice reported equivalent effects performance.The theoretical importance
of practicein young and old subjectswith concernsthe issueof what is responsiblefor
a tachistoscopicperceptiontask (Hertzog, the observedage differencesin short-term
Williams, & Walsh, 1976), a typing task situations. If experiential factors such as
(Leonard& Newman, 1965),and a mem- lack of relevantrecentpracticeare responory-scanningreaction-time task (Madden sible for the initial age differences,then
& Nebes, 1980). Poon, Fozard, Vierck, moderateamountsof practicemight lead to
Dailey, Cerella, and Zeller (Note I ) pro- the elimination of those age differences.
vided subjectswith the opportunity for ap- However,if physiologicalor biologicalfacproximately2 hr. of practicein a choicere- tors are involved,then it would be unlikely
action-time task and observed that old that any amountof practicewould result in
subjectsimprovedmore (i.e., reducedtheir the disappearance
of age differencesin perreactiontimesby a greateramount)than did formance.
youngsubjects.Despitethe greaterimprovementby the old subjects,however,the young Current Study
subjectsin this study still respondednearly
previously(i.e.,
The threeissuesdiscussed
twice asfast asthe old subjectsin the second
(final) session.
Jordanand Rabbitt (1977) Doesperformanceimproveon simpletasks?
also reporteda trend for greater practice- What is responsiblefor the improvement?
relatedreactiontime changesin older than Are there adult age differencesin the type
in young adults,but the statisticalanalyses or magnitude of improvement?)servedas
weresomewhatconfusing,and it is not clear the primary goalsof the presentstudy.There
whether the interaction of Age X Practice were two phasesin the project. In the first
was significant.A similar task, but with a phase,50 young adults and 24 older adults
much more dramatic outcome, was em- performedthe "SpaceTrek" game(consistployedby Murrell (1970).This experiment ing of signal detection,memory-scanning
usedonly three subjects,two teenagersand reaction time, visual discrimination, and
tasks)for a singlesesa 57-year-oldwoman, but each performed temporal-anticipation
for many hours,in over 12,000trials. The sion to determine the normative levels of
resultof major interestin the Murrell study performancefor the two age groups.In the
was that the reactiontime of the older sub- secondphase,8 young adults and 8 older
ject, althoughinitially greater than that of adults performedthe SpaceTrek game for
over a periodof 2either younger subject,eventuallyreached 5l experimentalsessions
the level of, and indeed became indistin- 5 mo.
guishablefrom, the reaction times of the
The effectsof practicecould be examined
youngersubjects.As intriguing asthis result by comparingperformanceat variouslevels
may be, it is important not to overlookthe of experiencewith the tasks. The mechafor any improvementthat
fact that the major conclusionis basedon nismsresponsible
the performanceof one 57-year-oldwoman! might occur were investigatedwith the use
The relationshipbetweenamount of ex- of severaltransfer conditions,and the peri-
odrc tntroduction of a
trmc task. One transfi
c h a n g i n gr h c q u a l i t a r i v
uli uscd in rhe rask- lr
the performance imprr
the developmentof a sti
anism. then the trant
should become progrc
r+ith increased expcric
transfer condition cons
ther the spatial sizeor tl
of the stimuli. The assu
if performance impror.r
creasein availableprocc
one should be better abl
under these demanding
practice than earll in
r a t r o n a l eg u i d e d t h c i n
current task. with react
ondarl task now scninl
c
D
F.gz.rt
Srrmulus rlcm3 usod u
, { g.cn rubrdl rccrrtd
:.5
r:crns end anoftrr ruh
trl.lr€
!:cas ,
SKILLED PERFORMANCE
odic introductionof a concurrentreactiontime task. One transfer condition involved
changingthe qualitativenature of the stimuli usedin the task. It was assumedthat if
the performanceimprovementwas due to
the development
of a stimulus-specific
mechanism, then the transfer to new stimuli
should becomeprogressivelymore difficult
with increasedexperience.A quantitative
transfer condition consistedof reducineeither the spatialsizeor the temporaldura-tion
of the stimuli. The assumptionherewasthat
if performanceimprovesbecauseof an increasein availableprocessing
resources,
then
oneshouldbe better ableto performthe task
under thesedemandingconditionslater in
practice than early in practice. A similar
rationale guided the inclusion of the concurrent task, with reactiontime in the secondary task now servingas the measureof
t82
"spare
capacity." Possiblechangesin the
processes
usedin carrying out the task were
investigatedby examining specific dependent variables within each task (e.g., the
slopeof the function relating reactiontime
to set size in the memory-scanningtask).
Becauseadults in two different age groups
served as subjects,the magnitude of im_
provementand the mechanismsresponsible
for improvementcould be directly compared
in the two age groups.
Method
Apparatus
A PDP I l/03 laboratory computer was used to pre_
sent stimuli on a Hewlett-Packard l3l lA Display and
record responsesfrom two l0-key telephone keyboards.
Koss PRO 4AA headphonesand a Hunter Model 3205
voice-activatedrelay were used to present auditory stim_
uli and register vocal responses.
Subjects
':
A
n
A
H
!
.
i
:
"2"
z
i
zi
i
'3
'
f ;gure I . Stimulus items used in the memory-scanning
:rsk (.{ given subject received one subset, e.g-, A, as
:\brtr\e ltems and another subset, e.g., B, as negative
: : c r n s).
Young participants were recruited from the universitv
community, and older participants from senior citizen
groups and referral from previous participants. All subjects reported themselves to be in reasonably good
health. Further characteristics, including the Wlchster
Adult Intelligence Scale (WAIS) Vocabulary and Digit
Symbol raw scores,are presented later, in Table l.
Experimental Tasks
Signal detection. In this task the subiect viewed a
display screen with a randomly varying pattern of 60
dots for 250 msec. The target, which appeared in approximately 507oof the observation intervals, consistid
of a configuration of 5 of the 60 dots subtending a visual
a n g l eo f a p p r o x i m a t e l y . 4 oa n d m o v i n g a t a r a t e - o fa b o u t
6" per sec in a consistent direction across the screen.
The direction of target movement varied randomly
across trials. Presenceor absenceof the target was indicated by the subject pressing a key on the right (for
yes) or the left (for no) keyboard. Accuracy feedback
was presented after each response.
Memory scanning. In this task the subject inspected
a list of one to four stimulus items (varied randomlv
across trials), and then rapidly classified a probe ite;
with respect to whether it was in the earlier memory
list. Forty stimulus irems were constructed from a 5 i
7 matrix subtending a visual angle of approximately
2.3" x 3.2". The symbols had approximately the saml
average number of matrix elements and overall com_
plexity as letters and digits, but all of the symbols were
unfamiliar and did not have readily available verbal labels. The set of 40 stimulus items was divided into four
lO-item subsets, as indicated in Figure l. For a given
subject, one of the subsets served as the population of
possible positive items, and another served as the pop-
183
TIMOTHY A. SALTHOUSE AND BENJAMIN L. SOMBERG
ulation of possible negative iterns. With the exception
of the transfer conditions, only members of the positive
subset ever appeared in the list of l-4 memory items.
The assignment of subsets as positive or negative was
balanced across subjects within each age group.
The probe stimulus, which was randomly selected
from the memory list or the negative subset, was classified by a key press on the right (for yes) or on the left
(for no) keyboard. Information about the accuracy and
speed (on an analog scale) of the response was displayed
immediately after the response.
The visual-discrimination
Visual discrimination.
task consisted of two visual arrays: squares and diamonds for one half of the subjects (Figure 2a), Xs and
*s for the other half of the subjects (Figure 2b), with
each array having a .5 probability of containing a target
e l e m e n t . O n e o f t h e a r r a y s h a d f o u r 2 . l o s q u a r e s( o r
Xs) positioned at the corners of an imaginary 27o rectangle, with a .6o diagonal (or for the Xs, horizontal or
vertical) line in one corner of one of the squares (or
o
Xs) as the target element. The other array had four 2. I
diamonds (+s) positioned in the middles of the sides of
the imaginary 27" rectangle, with a .6" vertical or horizontal (for the *s, diagonal) line in one corner of one
of the diamonds (*s) as the target element.
The two arrays were presented either in immediate
successionfor 400 msec each, in which case full attention could be devoted to each array, or simultaneously
for 400 msec, in which case attention had to be divided
between the two arrays. Simultaneous and successive
displays were randomly intermixed within trial blocks.
Two independent responseswere required in this task,
one indicating the presence or absenceof a target element in the square (x) arrays, and another indicating
the presenceor absenceof a target element in the diamond (+) arrays. Responsesconsisted of keypresseson
the left responsepanel for one array and keypresseson
the right responsepanel for the other array. Separate
feedback for each response was presented after both
responses had been registered.
No poststimulus mask was presented, and thus there
was some iconic persistence that allowed information
extraction to continue after the termination of the display. The luminance of each array was the same in the
successiveand simultaneous displays, however, and with
no delay interval between successivedisplays the duration of the persistenceshould have been equivalent in
the two-display conditions.
In this task the subject was
Temporal prediction.
required to anticipate the intersection point of two trajectories. One trajectory was primarily horizontal from
left to right with a speed that varied randomly between
22.5" and 45.0o per sec across trials. The other trajectory was vertical from bottom to top with a constant
speed, either 60o or 150'per sec, but had a variable
starting location along the horizontal axis. The subject
had control over the time of initiating the vertical trajectory with the goal of trying to make the two trajectories intersect one another at the same point in time.
When this occurred a visual explosion was displayed on
the screen and a crash sound was presentedthrough the
earphones. A key on the right response panel was used
to initiate the vertical trajectory.
The experimental tasks were embedded in the context
of a game called Space Trek, with the signal detection
"radar watch," the memory scanning
task identified as a
"UFO
classification," the visual discrimination
task as a
"weapons
scan," and the temporal prediction
task as a
"photon torpedo." The probability of a signal
task as a
in each of the first three tasks was .5. and thus, on the
average, 507o of the radar watches were followed by a
UFO classification. 507oof the UFO classifications were
followed by a weapons scan, and finally, 507o of the
weapons scans were followed by a photon torpedo. Note
that although the tasks were embedded in a game context, they were discrete and independent activities with
sequencing determined without reference to the subject's performance.
Alternate versions of the /asks. Both qualitative and
quantitative versions of the basic tasks were created that
were similar in format to the original tasks but differed
in an important respect. The qualitative versions of the
tasks involved different stimulus items in the signal detection (radar watch), memory scanning (UFO classi
fication), and visual discrimination (weapons scan)
tasks. The alternative stimuli in the signal-detection and
memory-scanning tasks were similar in structure, but
different in identity, to those used in the standard versions of the tasks. For example, subjects receiving Sub-
A
T
o n
o
n
o
O
X
+ X
-r
+
B
X
T
+ X
Figure 2. Stimulus arrays in simultaneous-presentatlon
condition in the visual-discrimination task. (One half
of the subjects received the arrays in A, and one half
received those in B.)
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SKILLED PERFORMANCE
sets A and B as the positive and negative sets in the
memory-scanning task now received Subsets C and D
in their place. The alternative stimuli in the visual-discrimination task consistedof Xs and *s in the locations
previously occupied by the squares and diamonds, respectively,or vice versa, depending on the standard version of the task for that subject. The targets to be detected remained as either vertical or horizontal lines or
diagonal lines in one segment of one of the items. There
was no qualitatively different version of the temporalprediction (photon torpedo) task.
Quantitatively different versions of the tasks were
created by reducing the stimulus duration by one half
in the signal-detection (from 250 to 125 msec) and visual-discrimination (from 400 to 200 msec) tasks. and
by reducing the size of the probe stimulus (from 2.3o X
3.2" to 1.2" X 1.6') in the memory-scanning task. No
quantitative variation was introduced in the temooralprediction task.
The memory-scanning task also involved a reversed
assignmenttransfer version in which the stimulus items
previously used as the positive set were switched to the
negative set, and vice versa. For example, a subject who
had received Subset A as the population of positive items
and Subset B as the population of negative items in the
standard version, now received Subset B for the population of positive items and Subset A for the population
of negative items.
Procedure. The experiment had two distinct phases.
In the short-term phase, 50 young (ages l8 to 23 years)
and 24 old (ages 60 to 79 years) adults participated in
a single one-block session consisting of 100 signal-detection trials, approximately 50 memory-scanning trials,
approximately 25 visual-discrimination trials, and approximately I 2.5 temporal-prediction trials. In the longterm phase, S young (ages 19 to 27 years) and 8 old
(ages 62 to 73 years) adults participated in the first oneblock session and in 50 additional two-block sessions
that each involved a total of 200 signal-detection trials,
approximately 100 memory-scanning trials, approximately 50 visual-discrimination trials, and approximately 25 temporal-prediction trials. In both phases,
one half of the subjects in each age group received one
standard version of the tasks and one half received a
different standard version. No performance differences
were evident across the two versions. A l0-min demonstration segment illustrating how each of the four tasks
was to be performed was presented prior to the experimental block of trials in the first session.
Long-term subjects were presented with quantitatively different versions of the tasks on Sessions 8 and
34, with qualitatively different versions on Sessions I I
and 37, and with the reversed stimulus-resoonse assignment version of the memory-scanning tas-kon Sessions l4 and 40. In addition, a vocal reaction-time task
was performed before and after the primary tasks on
Sessions4, 5, and 6, Sessions24, 25, and 26, and Sessions 44, 45, and 46. On Sessions5. 25, and 45 the vocal
reaction-time task was also performed concurrent with
the primary tasks.
The signals in the vocal reaction-time task were auditory tones presented at random intervals l-10 sec
apart, and the response was the word "pip" said as
quickly as possible.Sixty tones constituted a trial block.
One trial block was administered before and after the
184
primary tasks, and six trial blocks were administered
in the concurrent condition. The concurrent vocal reaction-time task started 2 min after the beginning of
the primary tasks, and ended several minutes before the
completion of the primary tasks. This procedure, and
the instructions to the subjects to concentrate most on
the primary task, were designedto encourage treatment
of the vocal reaction-time task as the secondary, rather
than primary, task in the dual-task situation.
The long-term subjects participated for I hr. per session, with most subjects performing one sessionon each
of 5 days during the week. Four weeks after the completion of Session50 the subjects participated in a final
follow-up sessionto determine the amount of forgetting
during a l-mo. period without intervening practice.
As a check of motivational effects on performance,
on Session 48 the long-term subjects were offered a
monetary bonus of $.10 for every millisecond they were
faster than their previous fastest time in the memoryscanning task, provided that they committed fewer than
I 09o errors.
Results
The principal measuresof performance
for the four tasks were the area under the
receiver operating characteristic (ROC)
curve,a measurecloselyrelatedto percentage correct derived from signal-detection
theory(Green& Swets,1964)for the signaldetectiontask, the reactiontime in milliseconds and the percentageof incorrect responsesin the memory-scanningtask, the
percentageof correct decisionsin the successiveand simultaneousconditionsin the
visual-discrimination
task, and the percentage of "hits" (intersectionsof the vertical
and horizontaltrajectories)in the temporalpredictiontask.
Becausetherewereso few trials per block
in the temporal-predictiontask (an average
of 12.5),and so many variationsin target
speed(horizontaltrajectory) and launchposition (vertical trajectory), performanceon
this task was analyzedby collapsingdata
acrossSessions
2 through l6 and acrossSessions36 through 50. This precludeddetailed
examinationof specificpracticeor transfer
effectsand thereforeis not discussedexcept
to mentionthat youngadultsweremore successfulin all conditionsthan older adults.
SessionI Analyses
The initial analysesfocusedon examining
agedifferencesin the SessionI data for the
short-term and long-term subjectsand determiningthe representativeness
of the long-
r85
TIMOTHY A. SALTHOUSE AND BENJAMIN L. SOMBERG
signal-detectionperforterm subjectswith respectto the larger sam- 4. It is clear that
for both young
dramatically
increased
mance
to
relevant
plesof short-termsubjects.Data
and old subjects.An analysisof variance
lheseissuesare presentedin Table I'
three levelsof pracTable I indicatesthat the two age groups conductedon the data at
and 42-45)' re(Sessions
2-5,22-25,
tice
in both the short-termand long-term sam14) : 2g'3''
F(1,
age,
significant
vealed
performance
plesdifferedsignificantlyon all
F(2, 28\:
practice,
-"utut"t exceptthe percentageof errorsin MS":9s1,5, p < .00i,
a
n d A g eX
<
.
0
0
1
,
task' In all casesthe 8 1 . 4 5 ,M S " : 2 5 . 0 , P
the memory-sCanning
:
25'0,
MS":
12.66,
28)
F(2,
Practice,
older subjects performed at a lower level
to
appears
interaction
The
effects.
p
<
.001,
than
(either slower or with less accuracy),
^be
a
ceiling
to
at leastpartially attributable
the youngersubjects'In contrastto the age
limiting performanceimprovementin
effect
slight
were
differences
sample
the
diffirencJs,
young
subjects,as they reacheda p:'
the
The long-termyoungsubjects
to nonexistent.
much earlier than the
plateau
formance
scores
had significantlyhigher vocabulary
wereminimal,
differences
Sex
subjeits.
older
memory-scanthe
in
and error percentages
malesin each
three
the
nins task than did the short-termyoungsub- ason Sesiions 42-45
Positions
worst)
(from
to
best
ranked
young group
iecis,but no otherdifferencesin either
and Posubjects,
young
the
6
in
and
1,
3,or old sampleswere significant.
subjects.
old
in
the
7
5.
and
3.
sitions
memthe
of
Becausemany of the analyses
An analysisof varianceconductedon the
ory-scanningdata involvecomparisonsas a
criterionmeasureof
functionof the numberof itemsin the mem- nonpa.a-etric response
(Hodos,
1970) revealedno
bias
perientage
ory set, Figure 3 was preparedto illustrate
Age X Practice
or
practice,
age,
iignificant
the relationshipbetweenmemory-scannlng
indi51.047o,
was
grand
mean
performanceand set size.Analysesof vari- efects. The
yes
than
no
more
make
to
tendency
a
ance revealedthat the effects of age F(1, cating
responses.
a
n
d
, S " : 3 2 0 , 9 9 5 . 7 ' P< . 0 0 1 ,
8 6 ) : 8 0 . 9 8M
the display durasetsize,F(3, 258): 44.66,MS": 13,071'3, ihe effectsof reducing
msecon Sessions
125
to
p < .001,but not sample(F <-1), weresig- tion from 250 msec
averagingthe
by
analyzed
were
34
nificant in the reaction-timedata. The set 8 and
and l0 and
6,7,9,
on
Sessions
performances
s i z e ,F ( 3 , 2 5 8 ) : 5 5 . 2 9 ,M S " : 4 1 ' 5 , P <
serveas
to
36
and
:
33,35,
32,
Sessions
on
4'7n'
25t)
F(3,
.001, Age X Set Size,
transcomparing
then
< .01,andSamPleX SetSize, control measuresand
MS.: 4t.5,p
-8.18,
analysis
in
an
performance
control
versus
MS": 41.5'p < .ool, ef- fer
F(3; 258):
in the transfersesfects were significant with the error per- of variance.Performance
in the control
than
worse
slightly
was
sions
qualitative
(Although
the
centage data.
l4) : 3'36'
(.858
F(1,
.835),
vs.
trendJare unequivocal,one shouldnot place sessions
did not
effect
this
but
p
<.05,
MS.:6.'7,
rnuch confidencein the quantitative relapractlce'
or
age
with
significantly
interact
because
tionshipsbetweenage and set size
duration thus seemsto
of the small number of trials per subject Halving the display
effects early
equivalent
producE roughly
and the extremelyhigh error rates.)
(Session
in practice,
34)
(session
late
and
8)
Takentogether,the resultsof Table I and
practice
The
adults.
old
young
and
with
and
Figure 3 indicatethat the long-termsubjects
analysis
this
significant in
are generallysimilar in initial performance effect wai also
M
1
4
)
2
3
'
4
7
, S":
F
(
1
,
(
.
7
8
5
vs..905),
to laiger samplesfrom their respectiveage
improvement
an
indicating
p
<
.001,
100.2,
g.orrpi, and that substantialage differences
6-10 and 32-36.
ire evidentin eachof the experimentalmea- betweenSessions
the target configchanging
of
effects
The
suresexamined.
37 were analyzed
1
and
I
urationon Sessions
bv averaqingperformanceson Sessions9,
Long-Term AnalYses
35, 36, 38,
rO. tZ. unali and on Sessions
and then
measures'
control
as
serve
to
39
and
under
areas
mean
The
Signaldetection.
perforcontrol
versus
the ROC curve for young and old subjects comparing transfer
Neither
variance'
of
analysis
in-an
*un""
are displayedin Figure
acrossthe 5l sessions
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187
L. SOMBERG
TIMOTHY A. SALTHOUSE AND BENJAMIN
the transfereffectnor any of its interactions
with age or practice were significant' Apparentl-y,youngand old subjects,both.early
lnd tat!'in prictice, can transfer their detection abilities equally well to a noveltarget
in the same display context' Performance
irnp.ou"awith piaciice('825 vs' '910),F(1, e
14\ : 26.02,MS": 44.4,P < '001,between
9-13 and 35-39'
Sessions
of introducing a concurrent
effects
The
vocal reaction-timetask on Sessions5, 25,
and 45 were analyzedby averagingperfor3, 4,6, and7, on Sessions
manceson Sessions
43, 44,
andon Sessions
27,
and
23,24,26,
46',and47 to serveas control measuresand
th"n "o*puring concurrent versus control
inan analysisof variance'Sigoerformance
nal-detectionperformancewas slightly-imoairedwith a concurrenttask('862vs' '845)' Figure 4.Mean signal-de,*'t" *'t""ance
for young
, S , : 6 . 5 ,P 1 ' 0 1 , b u t anf old subjects a-sa function of practice' (ROC = ref ( t , t + ) : 1 1 . 3 7M
the interactionswith practiceand age were ceiver operating characteristic')
Performing a simulta.neous
not significant'
-reaction-time
task therefore hinders
vocal
The final manipulationexaminedwith the
but the magnitudeof impairnerformance,
'ment
data was the effect of a lis about the same at three levels of sisnal-detection
the 50th and 5lst sesbetween
d"luy
^-o.
practicefor both young and old adults'
riont- Conttol performancewas determined
on Sessions49
ty the averagaperformance
with the decontrasted
tlis-was
and
una SO
(Session5l) in an anallayedperformance
The delay effect was sigurit
" n i nof
c avariance.
nt
( . 9 3 1v s . . 9 1 3 ) 'f ( 1 , l 4 ) : 6 ' ! 3 . '
US.: 4.1,p <.05, but the interactionwith
u!""*ut nof. lmposing a a-1vktinterval be1200
sessionsof the signal-cle'
tween successive
uJ
n
o
tection task thus seemsto have approxtU
=
matelythe sameslight impairmenteffecton
q, 1000
E
t
l
i
young and old adults.
both
Uimorl scanning' All data subjectedto
'R
Young
were
800
analysisin the memory-scanning.task
o
abnormatly
with
trials
remove
to
first edited
t
short (lessthan 100 msec)or long (greater
than 1,500msec)reactiontimes' The mean
reaction times and percentagesof correct
e
o
responsesfor the young and old. subjects
ul
are displayedin Figure
u"-tt the 51 sessions
',0s
ns 42-45the threemalesin each
5. On Sessio
srouD ranked, from fastestto slowest,Poiitlons l, 4, and 7 for the young subjects'
and Posiiions3, 5, and 8 for the old subjects'
Setsize
In an attempt to examine the tYPe of
function
Figure 3. Reaction times and error rates as a
search processused in memory scaming'
set sizes for young and old shortoi't"rnoty-..unning
reactiontimeswerecomputedseparatelyfor
term and long-term subjects, Session l'
% wI
sho( I.'m
F
6
sioil'hrm
loio lt.n
:.:
.\
v - .
t
' k
t
^-'*
gr
l;vrc
!
,r."n ,."o*..,r-
--_<?!.x)n-saanntnt
lask for rqr
i-lrrrn
of pracricc.
F)slttve and negativc tri:
F rgure 6 illustrates thcsc
of practice.An analy.sisr
a srgni6cantinteraction
Tlp.. fl:]. 42) = 43.21
ffi1. rndicating a shallo
:rrc than for positivetria
rtcm l. Figurc 6 suggcsts
ferences are primaril;- <
rponscs for positive one-it
end rhcn the onc-item tri
thc Sct Sizc x Trial T1p
txr thc remaining data fn
through four was not sigr
I _r4.,|/S.=5il.8.p>.
14 mscc'irem). This pau
gests rhat the scarch pn
crhaustive scarch condl
tremell rapid compansr
ortc-rlem pcitive s€t. (SG
addirional discussionof tl
srzc phenomenon.) It is
horever. that in neithcr
rere thc tnplc intcraoro
practicc significant. l*'ha
ttrc ecarch proccss. tbcrc
dd nrt diffcr as a funcl
rub_rccragc.
Frgurc ? portrar-s rcacl
ntc as a function of sct d
lqrot and old sublcrs.
rsrr conduoed oo thc
r88
SKILLED PERFORMANCE
3
5
7
9
11 j 3r517192123?527293r 333537394143154719
Sessron
Figure 5. Mean reaction times and accuracy in the
memory-scanning task for young and old subjects as a
function of practice.
error-ratevariables.All main effectsand interactionsweresignificantwith the reactiontime variable:age, F'(1, 14) :46.92, MS.
: 41,894.3,p < .001; set size,F(3, 42):
15.21,MS": 997.4,p< .001;practice,F(2,
28) : 37.Ur,MS.: 10,009.0,
p < .001;Age
X Set Size,F(3, 42) : I1.64, MS" : 997.4
p < .001;Age X Practice,
F(2,28): 22.35,
MSe: 10,009.0,
p < .001;Set SizeX Practice, F(6, 84) : 12.19,MS" : 511.2,p <
.001;and Age X Set Size X Practice,F(6,
84):8.24, MS": 511.2,p : .001.The effectscan be seenin Figure 7. Older subjects
and larger set sizesproducedthe longestreactiontimes,but theseeffectsbecamesmaller
with practice. Separate analysesat each
stage of practice revealedthat age, F'(1,
14) > 19.7,and set size,F(3, 42)> 58.7,
effects were highly significant throughout
practice,but that their interaction became
w e a k e rF: ( 3 , 4 2 ) : I l l 0 , 5 . 2 0 ,a n d 3 . 0 1a t
Sessions2-5, 22-25, and 42-45, respectively. Slopesof the set-size- reaction-time
functionson Sessions42-45 were27 and 33
msec/item for young and old subjects,respectively,with all set sizes,and 14 and 15
msec/item,respectively,
for only set sizesof
2, 3, and 4. With the error variable,significant effectswereobtainedfor age,.F(1,14)
= 7.26,MS": 215.6,p < .05;setsize,.F(3,
42):21.9t, MS": 15.1,p < .001;practice,
F(2, 28): 14.55,MS.: 74.9,p < .001;
Age X Set Size, F(3, 42\: 4.70, MS":
positiveand negativetrials for eachset size.
Figure6 illustratesthesedata at threelevels
of practice.An analysisof variancerevealed
a significantinteractionof Set Size X Trial
Type,F(3, 42) : 43.21,MS,: 453.3,p <
.001, indicatinga shallowerslopefor negative than for positivetrials (31 vs. 49 msec/
item). Figure 6 suggeststhat the slopedifferencesare primarily due to the fast responses
for positiveone-itemtrials, however,
andwhenthe one-itemtrials wereeliminated
the Set Size X Trial Type interactionbased
on the remainingdata from set sizesof two
throughfour wasnot significant,F(2,28) :
1 . 3 4M
, S . : 5 l 1 . 8 , p> . 1 0( s l o p e:s 2 2 a n d
24 msecfitem). This pattern of resultssugf '--l
FH
|toil'h
I
geststhat the searchprocesswas a serial,
/
exhaustivesearch conductedafter an extremely rapid comparisonof the previous 7m
U
one-itempositiveset.(SeeClifton, 1973,for :
additionaldiscussionof the fast one-itemset ; m
-'
F' /_--*
I
size phenomenon.)It is important to note, . E s
however,that in neither of these analyses d9
werethe triple interactionsinvolvingage or
"/
practicesignificant.Whateverthe nature of
the searchprocess,therefore,it apparently
did not differ as a function of practice or
subjectage.
1
2
3
4
1
2
3
a
r
2
3
a
Figure 7 portraysreactiontime and error
Sotsi:6
Sgbire
S€tsite
rate as a functionof set sizeand practicefor
Figure
Mean memory-scanning reaction times for
\oung and old subjects.Separateanalyses positive 6.
and negative trials as a function of set size, age,
uere conductedon the reaction-timeand and practice.
I
)
:
i
r
LI
t
s
e
h
t-
s.
)f
,
)r
tt
NqrY.
e--i
L--{
|
,lI
/'r- l "'7
/-i | /--:
'/l'"f
189
SOMBERG
TIMOTHY A. SALTHOUSE AND BENJAMIN L.
15.1,p < .01;and Set SizeX Practice,F(6,
84) : 4.95,MS.: 10.4,p < .001'.Reaction
time wasfasterbut error rate washigherfor
vounq subiects relative to older subjects,
trad.e^ittur iugg"iting that a speed-accuracy
off waifartially responsiblefor the age differencesin reaction time. With the other
effects,however,both reaction time and er- o
ror rate increased,and thus a speed-accu- Uo
racv trade-offcontaminationis unlikely'
The effects of reducing the size of the tr
8 and o
probestimulusby onehalf on Sessions
peraverage
the
using
by
analyzed
*"t"
34
formanceson each set of four adjacentses.iont tO,7,9,and l0 and 32,33,35,and 36)
as control measures'and then companng
transfer versuscontrol performancein an
analysisof variance.These data are illustrated in Figure 8. The size reduction had
:
a significanimaineffect,F(1, 14) 50'96'
MS": 24,796.9,P < '001, and an interacSetsizo
tion with age, F(1, 14):9'1', MS":
vari- Fisure 8. Mean memory-scanning reaction times.and
J.Ot on the reaction-time
24,'796.9,p
:
l8'65'
eiior rates in control and reduced stimulus conditions
14)
F(1,
abie. Sizi reduction,
rinl, ""a bars indicate performance in the control
MS.: 64.5,p < .001, and the interactio-n iSorio
relers
condition. Early referc to Sessions6-10 and late
of Age x Sei Size X Size Reduction,F(3' to Sessions 32-36.)
4D: 4.41,MS": 21.9,p < .u: weresignidcantwith the error variable'The practice
greater overall reaction time (612 vs' a]-5
main effect was significanton the reaction:
ilsec), but the absenceof an interactionwith
time variable, F(1, 14) : 20"72, MS.
that the slopesof the funcp < .001,asreactiontime changed t"t tir" suggests
16,508.7,
size to reaction time were
set
6-10 tion relating
from 580'to 508 msecfrom Sessions
The Age X Size Reduction inaffectedl
not
to Sessions32-36.
indicates that the older subjects
The main effectof sizereductionindicates teraction
greater
increasein reactiontime with
a
that the smaller probe stimulus leads to had
than the young subjects
stimuli
the red'uced
(196 vs. 79 msec).
The effectsof changingto new stimulus
items on SessionsI I and 37 were analyzeo
B [ B
bv using the averageperformanceson sesrio* g,io, 12,and-Ii and 35, 36, 38, and
:g us contiol measuresand then comparing
--""tt'
transfer versus control performancein- an
- "'tanalysisof variance.These data are rllus,""'ti"t.ia in Figure 9. The stimulus-change
maniputatioriwassignificant-with both-the
t
r e a c t i o n - t i m eF, ( 1 , l 4 ) : l 3 ' 8 8 ' M S " ::
F(l' la)
a
6244.5,p< .01,and error-rate,
aswas
variables'
p
<
'01,
'3,
47
13.61,'MS":
interaction:
Size
itt" Sfi-utut ChangeX Set
r"u"tion time,F(3,42) : 6.38,MS.: 642'6'
=
Fisure 7. Mean memory-scanning reaction times.and
, . .Of, error rate,F(3,42) 12'89'MS":
'11.2.
old
erior rates as a function of set size for young and
p < .001. The Stimulus ChangeX
d
gdze
subjects at three levels of practice'
Yeng
-:^g -
:(g -
{--.t-
.i-'
": n'lh-th
Oi
t
a
:
rr-
j
,-
.
gt9r. I -
"'-
/
-
.,/
^
t
a
7 - 0 . ._ _
f :gre 9. Mcan mcmory-scear
"::J{ rat6 In control and ncr {r
-:rs and bars indicatc pcrforn
:.:r:n farl.t.refcrs lo Scssroo
\dsrorls -15- 39. )
Practice interaction was r
crror-rate variable. F( l.
' - l 1 . . 1p. < . 0 5 . i n d i c a t i n
rclative to old stimuli. ha
rn practice than carll'- Al
rant effects involving th
factor were evident only.
rariable: Stimulus Chal
Agc. r(1. 42) = 4.58. M:
and Stimulus Changc x
R l . l a ) = 5 . 2 8 .M S . =
though rather complex, I
tcractions is consistent r
tron that a spccd-accu
rcsponsiblc for thc reaoi
results. Reaction-timc
proved betwecn Scssions
{ i I I vs. {63 mscc).F( l. t
9-r-6{.p<.O1.
Tlrc eristencc of an in
rr.?c sugg6ts rhar shiftin
rrrmulus itcms affecrs rhc
:rxr rclatrng reaction tirnc
$c dopcs serc J9 and :
rFclrrclr.
for normal r
ncans An anallsis condr
{rE-rtcm rt-sizc dara al
SKILLED PERFORMANCE
190
nificant effect of stimulus change (390 vs.
4 0 7 m s e c )F, ( 1 , 1 4 ) : 5 . 8 3 , M S . : 7 3 2 . 9 ,
p < .05.Neither the interactionwith agenor
with practicewassignificantin this analysis.
The effectsof reversingthe setsof positive
and negativeitems on Sessions14 and 40
wereanalyzedby averagingperformanceon
12,13,15,and 16,andon Sessions
Sessions
E
o. 40o
o
38, 39, 41, and 42 to serveas controlmeaU
U'
U
E_ soo
sures,and then comparing transfer versus
o
control performancein an analysisof variE
tr
ance.Thesedata are illustratedin Figure 10.
The reversalmanipulation was significant
E 70o
with both the reaction-time,F(1, 14):
cc
23.37,MS":20,826.2,p <.001, anderrorrate, F(1, l4):55.62, MS.:28.5, p <
.001. variables.as was the ReversalX Set
Size
interaction:reaction time, F(3, 42):
o
u
14.88,MS" : 801.5,p <.001; error rate,
F(3,42) : 4.41,MS.: 30.8,p < .01.Other
significanteffectsinvolvingthe reversalmaFigure 9. Mean memory-scanning reaction times and
error rates in control and new stimulus conditions. (Solid
nipulation on the reaction-time variable
lines and bars indicate performance in the control conwere ReversalX Age, F'(1, 14) : 6.43,
dition. Early refers to Sessions 9- I 3 and late refers to
X
MS.:20,826.2, p <.05, and Reversal
S e s s i o n s3 5 - 3 9 . )
Practice,F(1, l4) : 5.13, MS.: 4,942.3,
p < .05. No other reversalinteractionswere
Practiceinteractionwas significantwith the significantwith the error-rate variable. In
error-ratevariable,.F(1, 14) : 5.39, MS. all casesthe direction of the error-ratedif: 31.4,p <.05, indicatingthat newstimuli, ferenceswas the sameas that for the reacrelativeto old stimuli. had more errors late tion-time differences.The main effect of
in practicethan early. All remainingsignif- practicewas not significantin the contrast
icant effectsinvolving the stimulus-change betweenSessions12-16 andSessions
38-42.
factor were evidentonly with the error-rate althougha reaction-timetrend wasapparent
variable: Stimulus ChangeX Set Size X (519 msecon Sessions
12-16,498 msecon
Age, F(3, 42) : 4.59,MS. : 11.2,p < .01, Sessions38-42).
and Stimulus ChangeX PracticeX Age,
As can be seenin Figure 10, the interF ( 1 , 1 4 ): 5 . 2 8 , M S " : 3 1 . 4 p
, < . 0 5 .A l - actionswith age and practice were due to
though rather complex,neither of thesein- greater reversaleffectsin old comparedto
teractionsis consistentwith an interpreta- young subjectsand late comparedto early
tion that a speed-accuracytrade-off is practice.The set size interaction indicates
responsiblefor the reaction-timepattern of that the slopeof the reaction-time-set-size
results. Reaction-time performance im- functionwasgreaterin reversedthan in norprovedbetweenSessions9-14 and 35-39 mal conditions(59 vs. 40 msec/item).The
( 5 1 I v s . 4 6 3m s e c ) , F ( 1l 4, ) : 1 6 . 6 9 , M 5 " : reversalmanipulationwasalsosignificantin
9376.4,
p < .01.
an analysisconductedonly on the one-item
The existenceof an interaction with set set sizes(389 vs. 436 msec),f'(1, 14):
p < .01,however
size suggeststhat shifting to a new set of 10.39,
none
MS.: 3,528.9,
stimulusitems affectsthe slopeof the func- of the interactionswas significant.
tion relatingreactiontime to setsize.Indeed,
The effects of introducing a concurrent
the slopeswere 39 and 52 msec/item, re- vocal reaction-timetask on Sessions5, 25,
spectively,for normal and new stimulus and 45 were analyzedby averagingperforitems. An analysisconductedon only the manceson Sessions
3, 4,6, and7, on Sessions
43,44,
one-itemset-sizedata also revealeda sis- 23,24,26, and 27, and on Sessions
q
E
800
TIMOTHY A' SALTHOUSE AND BENJAMIN L. SOMBERG
I9I
'x-,
46, and 47 to serveas control measuresand
then comparing concurrent versus control
Tlj
performancein an analysis-of.varianc":
Loncurrent-controlmanipulationwassignificant with the reaction-timevariable (491 2
v s . 4 7 6 m s e c ) ,F ( 1 , 1 4 ) : 9 . 9 5 , M S . :
tr
2,297.3,p <.01, but no interactionswith
age,praciice,or setsizeweresignificant'.No
effectsor interactions
c6ncurrent-condition
,"e
error-ratevariable'
the
with
weresignificant
E
,09
On Session48 a monetary incentivewas
offeredto determinewhether reaction-time
performancecould be improvedwithout saciin"ing accuracy.The averageperformance Figure 11.Mean memory-scanning
reactiontim.es.and
46 ind 47 servedas the control erior rates in control and speedincentive conditions'
on Ses-sions
measure.and the incentiveeffect was ana- (Solidlinesandbarsindicateperformancein the control
lyzed in an analysisof variance'Data from condition.)
Sessions49 and 50 were not included because of the possibility that the incentive
but error rate worsened (inmanipulation would result in a change in creased),
the incentiveconditions.The
subsequentperformance. This procedure creased),under
was significant with both
.""m"d justihed in light of the very small incentive factor
time, F(1, 14): 69'5''
reaction
variables:
practiceeffectsobservedduring this part of
<
MS":1,020.6,
P .001; error rate,,F(1,
ihe experiment(cf. Figure 5). Figure 1l il:
40'3,P < '001' The inMS":
2'7
.27
14\
(de,
lustratis that reaction time improved
14) : 4.61,MSg:
F(1,
teractionswith age,
=
1020.6,p <.05, and set size, F(3, 42)
:
sig5.38,M^t" 266.6,p <'Ol, were also
nificant with the reaction-timevariable'
Becauseof the oppositetrend with the
reaction-timeand error-rate variables,the
preciseeffect of providing a moneta.ryincentivefor improvid performanceis difficult
to evaluate.Reaction time decreased(435
vs. 392 msec),but error rate increased(6Vo
vs. l2Vo), and without knowing the exact
u
o
form of the time-accuracyexchangefunco
tion it is impossibleto determineif the two
E
i:
trends were completelycompensatory.The
remainingeffectssuggestthat older subjects
wereableto reducetheir reactiontimesmore
than young subjects(55 vs' 31 msec),and
that ihe set-size-reaction-timeslope was
shallowerin the incentivecondition (25 vs'
35 msec/item).
e
2 0 Y
The eiTectof a l-mo. delay betweenthe
12 U
f
was analyzedby con50th and 5lst sessions
1
2
3
4
1
2
3
4
49
performanceon Sessions
average
trasting
Setsize
(Sesperformance
and 50 with the delayed
Figure 10. Mean memory-scanning reaction times and
sion 5l) in an analysisof variance.Neither
erior rates in control and reversed assignment condithe delayeffectnor any interactionswith the
tions. (Solid lines and bars indicate performance in the
delay factor were significantwith either the
control condition. Early refers to Sessions l2-16 and
reaciion-timeor error-rate variable.In this
late refers to Sessions 38-42.)
I
E
o
t
2
t
ot"t"'t"'
2
\
r
Jt
i F
. -
r
,
\. s . . .
'
.-ta
.
,
'- :i :
\
a t t ' - . " a
i . .
t:'
_
j
!
.
-
l
r g...'1..
r^ '-
i
i
:
tr
1
-.-/r'i'.I
3
-
*
-
r '
,
\.."
t
l
,
'
. -t*
"
"'J
Frgure 12. Mean visualdrcn
e-cssivcand simultancous co
subJccts as a function of prr
particular analysis. hor
outcome may bc some
cause of grossly unequr
the loung subjectsand I
rncreasedtheir reaction
delar'. but one older s
reaction time bv over r
tributing to extremc val
5l dara. In view of rh
trend (13 of 16 subpc
rndicated in Figurc 5. i
defer a conclusion on sl
rncreascsover a l-mo. t
l'i suaI d iscriminat iot
of correct stimulus dis
succcssiveand simulul
the \oung and old subya
rons arc displal'cd in F
.lccts on Scssions 42-4j
to sorsr. Pcitions l. 1.5
subpcrs. and Positions
oid sub.pcts.
{n anall'sis of r.arianc
tbc dara ar thrce leyels o
: i. ::-:5. and {2-,15)
ead attcntron t succcssirr
'.roorrs -dirrdcd
) as fact
cfocrs rere signifcant
t{ 06. -r/S. = l7{.J. p <
li,= ll60..VS.=55.
SKILLED PERFORMANCE
192
tention,l'(1, 14) : 135.19,
MS": 6.8,p <
.001-but none of the interactionswasiiei'Pl 9 A
nificant. This pattern of results,in conjuni',1 5
tion with the trendsillustratedin Figuie 12,
Young
suggeststhat the divided-attentiondeficit
was approximatelythe samefor young and
old subjects,anddid not changeasa funttion
of experiencewith the task.
A more detailed analysisexaminedperformancein the simultaneouscondition as
a function of the presenceor absenceof a
R.,'
siglal in each array. The four trial types
differedsignificantly:signal,Array l-signal,
Array 2: 66.8Vo;
signal,Array l-no signal,
Array 2 : 74.l%oi
no signal,Array l-signal,
Array 2:7O.OVo;no signal,Array l-no signal, Array 2:83.4Vo; F(3, 42):9.74,
MS.:25,466.0,p
<.001. However,
thisefS€ssions
fect did not interactwith either ageor pracFigure 12. Mean visual-discrimination accuracv in suctice.
cessiveand simultaneous condilions for young and old
The effectsof reducingthe durationof the
subjects as a function of practice.
stimulus arrays from 400 to 200 msec on
Sessions8 and 34 were analyzedby averparticular analysis,however,the statistical aging performances
on Sessions6, 7,9, and,
outcomemay be somewhatmisleadingbe- 10, and on 32,33, 35, and 36 to
serveas
causeof grosslyunequalvariances.Sevin of controlmeasuresand then comparing
transthe youngsubjectsand six of the old subiects fer versuscontrolperformancein
an inalysis
increasedtheir reactiontimesoverthe l'-mo. of variance.The duration reduction
led to
delay, but one older subject increasedhis a decrease
in discriminationaccuracy(76.gvo
reactiontime by over 400 msec,thus con- vs. 70.07o),
F(1, 14) : 30.79,MS.: 49.4,
tributing to extremevariancein the Session p < .001, but no interactionswith
the du5l data. In view of the consistencvof the ration factor were significant.performance
(13 of 16 subjects),and the pattern was better on Sessions
Jreld
32-36 than on Sesindicatedin Figure 5, it is perhapsbest to sions6-10 (76.5Vovs. 7O.3Vo),
F(1, 14):
defer a conclusionon whetherreactiontime 14.09,MS": 83.9,p < .Ol. The
absence
of
increasesover a l-mo. delay.
interactionswith age and practice suggests
Visual discrimination. The percentages that variationsof subjectage or amount
of
of correct stimulus discriminationsin ihe experiencedo not affectthe susceptibility
to
successive
and simultaneousconditionsfor performance impairments with shortened
the youngand old subjectsacrossthe 5l ses- stimulusdisplays.The lack of an interaction
sionsare displayedin Figure 12. Male sub- with the attention(successive-simultaneous)
jects on Sessions42-45 ranked. from best factor indicatesthat
the magnitudeof the
to rvorst,Positions| , 2.5, and7 for the young divided-attentioneffect was essentiallv
unsubjects,and Positions3, 4, and 8 for the changedwhen the display duration *as
,eold subjects.
ducedby 507o.
An analysisof variancewasconductedon
The effectsof changingthe type of stimthe data at three levelsof practice(Sessions ulus arrays on Sessionsll and 37 *ere
an2-5, 22-25, and 42-45) with age, practice, alyzed by averaging performances
on Sesand attention(successive-focused
vs. simul- sions9, 10,12, and 13 and on 35, 36, 3g,
taneous-divided)as factors.All three main and 39 to serveascontrolmeasuresand
then
effects were significant-age, lc(I, 14) :
comparing transfer versus control perfor66.06,MS": 274.3,p< .001;practice,F(2, mancein an analysisof variance.The
stim28) : I1.60,MS.: 55.2,p < .001;and at- ulus-changefactor was not significant,
but
l'\,
o 7 0
,
3
5'
9.
1 3 t s r . 1 9 2 ,2 3 2 5 2 2
1 9 J lr r
39 4J 43 45 47 49
5l
193
L' SOMBERG
TIMOTHY A. SALTHOUSE AND BENJAMIN
ywng
wr?,
Accuracy (percentagescorrect)
changing stimulus Arrays on r.lisuar_Discrimination
Late (Session 37)
Early (SessionI l)
Group
Young
old
M
Normal
86.8
6l.7
't4.2
New
87.2
59.1
2.6
'13.r
l.I
New
Normal
Difference
93.5
65.0
't9.3
Difference
O
3
8 5 .I
64.3
8.4
.'7
1A
4.6
1
E
I
6
400
l-
E
300i
:
agesof six trial blocks each on Sessions5'
the interactionswith practice,F(l' l-4)
23, and 45. The means of these data are
6.22,MS,: l6'0' P <'05, andAge X Pracillustratedin Figure 13. The age effect was
ti"",'r(t'-t+\ : l/i.25,MS": 16'o'P < 'ol'
but
noi signifrcant(F < 1.0) in the analysis,
:676'04'
*"t" tignin"ant. Theseeffectscan be seen
14)
F(1,
""on"urtentfactor,
ln"
-is":568.1,
i" f"ttE 2. Note that the detrimentaleffect
p < .001'and its interactions
more
is
display
of changing the stimulus
: 58'23,MS': 568'l'
r(1,'14)
pronouni"Jlate in practice,and that young *iitt un"
28) : 24'34' MS:.^
F(2,
.
.OO'f
,
,
Piactice
iubiectsexhibit this trend to a greaterextent '292.8.p < .001, and Age X Practice''lu(z'
itruiiofa"t subjects'The practicemain effect
28) = j.00, MS.:292.8. p <.05 w.e.r:e^stcwas significait (73.9Vovs' 76'9Vo)'F\l'
(483 vs'
nin"unt. Reactiontime was slower
tij : 6.el , MS" : 51.1,p <. '05, indicating
perwas
356 msec)when the primary task
improvementbetween Sessions9-13 ano
was
difference
This
formed concurrently.
Sessions35-39.
subyoung
than
subjects
for older
The effects of introducing a concurrent n.Lut",
(164 vs. 89 msec),increased--practlce
iects
25'
5'
Sessions
on
task
uocai reaction-time
i;;J"d to reducethe difference(160 to I 17
unJ +s were analyzedby averaging-perforSessions5, 25, and 45' re'
3,4,6, and7' on Sesstons io f OZmsecfor
manceson Sessions
the -magnitude.gf th:,-t-"and
43' 44' spectively),
i{,2q,26, and 27, andon Sessions
for older subjectsthan
greater
was
duction
46, and47 to serveas control measuresand
(from
212 to 152to 128
i"in"t"e ,u6j""tt
itt"n "o-puring concurrent versus control
108 to 84 to
from
-r"t foiotaei subjects,
oerformancein an analysisof variance'Neisubjects)'
77 msecfor Young
itr"t ttt" main effect of the concurrent task
The absenteof a significantmain ellEct
or
practice'
age,
with
nor any interactions
quite unwere of age in a reaction-timetask is
attention (successive-simultaneous)
subof
light
in
particularlv
;;;?LJ,
,the mea---No
sisnificant.
other
in
observed
diiferences
.ignincant delay effectwas evident.in stantial
performance-with
5l
Session
of
the contiast
49 and
iii" uu".ug" performanceon Sessions
the
involving
50, nor were any rnteractions
factor significant.
delay
-o
iln rrr"nt-task. Performanceon the a
vocal
as the
concurrenttask wasrepresented
reactiontime, in msec,to the auditory sttmulus.Trials with latencieslessthan 100msec
or ntJ"t than 1,000msecwereeditedfrom
The remainingtrials were,anthe-analysis.
alvzedin an analysisof varianceat three
levelsof practicewith control measuresconof the averageof two blocksof trials
ritti"g"on
(solid
Sessions+, 5, and 6' Sessions2.4' Fipure 13.Mean vocalreactiontimes in control
"u"tt
for young
conditions
(dotted
lines)
lne
"on"urrent
46'
unO
iin?.i
and
44,45'
25,and26,andSessions
una ota tuUj""ts at three levelsof practice'
concurrentmeasuresconsistedof the aver500
F
E
45
Session
25
Sesson
45
-<
\
\-\
,*,
,
_
Ssron
Figure 14. Concurrent vca.l
ual subjects at three lcvcls o
sures with these samc
of the data from indivk
sizable individual dif
young subjects. Figun
differences with the nx
the concurrent conditk
Jects at three levels of
two young subjects r
tended to reduce their
increasedpracticc. tha
quite slow and exhibitc
reaction time with add
that three subjects w
speedand direction of <
The concurrent- contn
quite different, as thc fa
jects had averagevaluc
msecon Sessions5. 25.
*hereas the slowestthr
95. 87. and 85 mscc. n
Discus
For clarity' of prescnt:
tron \r'as organized in t
tasks. In the prescnt sc
tron is in terms of thc tl
s-ooc€min the pro;ect.
Improvement in Simplc
.\ strong conclusion I
*rlts rs that performarrc
ilodcratc crperiencc on
gtnal detcction. reactk
SKILLED PERFORMANCE
194
discrimination.The range of performance
improvementwas artificially limited by the
measurementscale in the signal-detection
and visual-discriminationtasks, but the
changeswith practiceare indisputablein all
o
three tasks. It is also noteworthythat the
3
performance improvement was relatively
E
stableover a l-mo. retentioninterval.
The conclusion that performance imtr
proveson simpletasksis really not very sur\
\
prising in light of the literature reviewed
\
earlier, but it has not yet been widely acceptedby researchers.
For example,actoroing to Ream's(1922) criterion of capacity,
noneof thesetaskswould be appropriateto
serveas a measureof an individual's fun_
Figure 14. Concurrent vocal reaction times for individ_
damentalability, becauseeachhas beendeual subjects at three levels of practice.
monstrated to exhibit sizable practice-related improvements. Nevertheless. tasks
sureswith these same subjects.Inspection similar to these,either in laboratoryor paof the data from individualsubiectsrivealed per-and-pencilforms, are frequentlyusedto
sizable individual differences among the assessan individual's ability or capacity.
young subjects.Figure l4 illustrates these Suchassessments
may still be usefulfor reidifferenceswith the mean reactiontimes in ative judgments,but they do not appearto
the concurrentconditionfor individual sub- be meaningful in any absolutesenie, and
jects at three levelsof practice.Notice that shouldno longerbe interpretedas reflections
two young subjects were quite fast and of the fundamentallimits of human perfortended to reducetheir reaction times with mance.
increasedpractice,that three subiectswere
From the skill perspective,the demonquite slowand exhibitedat leastone slower strationthat improvementoccursin elemenreactiontime with additional practice,and tary tasksis important, becauseit indicates
that three subjects were intermediate in that the development
of skill doesnot merely
speedand directionof changewith practice. involve the integration or coordinationof
The concurrent- controlmeasures
werealso fixedand staticperceptualor motor abilities.
quite different,as the fastesttwo youngsub_ The discoverythat even such very simple
jects had averagevaluesof 133,AZ.anOOS activities as detectingthe presenceor ibmsecon Sessions
5. 25, and 45, respectively, senceof a signal or making a rapid binary
whereasthe slowestthreesubjectr-uu"rug"d classification decision improve with in95,87, and 85 msec,respectively.
creasedexperiencesuggeststhat skill acquisition cannot be consideredsolely in
terms of the timing or coordinationof the
Discussion
components.The relative contributionsof
For clarity of presentationthe Resultssec- improvementsin the componentsversusimtion was organizedin terms of the specific provementin the integrationor coordination
tasks-In the presentsection,the orginiza- of the components
cannotbe assessed
at this
tion is in terms of the three major isiuesof time, but the importanceof changesin the
concernin the project.
elementaryprocesses
involvedin the acquisition of a complexskill shouldno longer be
in doubt.
Improvement in Simple Tasks
,rr.a
Young
:>>"
S
\5
500
F
=?<
25
Session
45
5
2
5
4
5
Session
A strong conclusionfrom the presentre_
sults is that performancedoesimprovewith Nature of Improvement
moderateexperienceon simpletaiks suchas
In the introduction,threebroad classesof
signal detection,reaction time, and visual explanation for practice-related
improve-
I95
BENJAMIN L' SOMBERG
TIMOTHY A. SALTHOUSE AND
mentinsimpletaskswereoutlined.Herew
e a n d t hi1d99d'
u s p e r fthe
e c t tsubiective
r a n s f e r mexperience
ighthavebeen
;,;"*
i"'utt'
task is of
considerthe relevanc";?;;";;"t
sum.- of"u lutg"t in the sisnal-ditection of the
to each classof explanation,and al-so
pattern
the
moving."but
r"*"tffig
':* "".1:"":_:ro, "u"t
In
marizesomeof tr," ot^rrlr""ui[n""
""bjgctis-never clearly denned.
;;;;
betposition.
been
have
::.
i"iiirni,,t111"^ryre, it might
rather
The first categoryof possiblemechanisms
ter to have varied the rate of motion
tr,e
in
;h;;ge
during
attributed i,,'prou"."ni;;;
dots
of
arrangement
;;";1h" spatial
type of information #i";p;:*t*
I.t,l";
qualitativetransfer sessions'
the
"'iil"-Gificant
something
that
spectiveanalysls ,ugg"Jtr'
Stimulus ChangeX Set
i"t[
like this occursin ,tl"rign"i-J",""r-o"
with reaction time in the
Si;^L;;""ti*
because subjects ,"p"o.T"i'riu,-il; _n:q-ii
task indicates that the
-memory
memory-scanning
learn what to look f"'j" 't'" Ai'ni"V' 111tt9* n"* rti.uri in
scanning had a
""J-"i"ra i"r*
with
reports are to b" b"#;;;
of gt""t"i-tf""t with largei set sizes-than of
tvpe
that improvemento".u., in part b.""uur"
the
in
shift
distinction. ildl ;;;t;Lr- Sin"t-u
a more precise rig";;-;;;J;
would be expectedto
had informationprocessed
Early in practicethe subjictsapparently
for stimuli preceded
result
same
the
fr-oIi ;;;t;"
diffiiultydistinguishing signatetbments
as for those preitem
memory-set
by one
"f"t
background noir" "r'Jill,i*:'#';;i;
"ia"J uv two,.three, or four memory-set
i"tti
some nonthey were able to p"*#;ih"'ngr."
Aoit G,,'t, thit finding suggeststhat
involved
form of a consistentl'*""f"g gt[up of
probablv
w-a=s
;;a;;;;;"hanisir
in the
werethey ableto i*p';;;h;i.ilrror-un"".
presented
were
;#;"";
*]l:tt
The principal manipu^lationdesigned.t"o
investigateapossible,.t,iftinthetypeof.in-memory-Scanningtask.(Butseethe.follow.
interpretation)' A
was also eviformation t"ing pro-""r.". *". in6'gualila- il-i;;.an,alteinative
effect
tri?nt ttitulus-change
unfamiliir
"onaitiiilin**r,i"t
transfer
tive
sizes'however'and
in prai- deit with one-itemiet
normal
stimuli werepresentedat two points
coding systemsdevelopedfor the
tice. The reasoningwas that if performance J'i,,,ti might be r"sponiible' The interaction
improvemen, *u, du? ;;;fu;lrr-rp^""iii
only with the eror nei wittr pract-icewas evident
mechanisms,then the introduction
direction was as
in p"t- toi-tut" variable' but the
late in pracstimuli should lead to a decrement
effect
a"u"r- pr"drci"a, *ith a greater
formance. For example, if subjectg.
than earlv'
---intioaucing
ior'coaing ttre tice
;;;-;-tGi"ri,"a'^t'vtilm
new stimuli in the visual-dissysternii
this.
siimuli, one would not expect
oroduceda larger reduction
tisk
unfamiliar stimuli werl' "tit"i;;iion
'untu:ttt:
on Session
be beneficialif new,
in-"""utu"v on Session37 than
howqualified
employed'
somewhat'
is
^
-.":-:-",
ii.-!il;;a*e
exhibThe amount or transfer to qualitatively
subjects
young
th"
onlv
tasts. rr"nr'- ever,because (see
different stimuli "";i;J;;;";,
Table 2)' The greater
ited sucha trend
signal-detectiJn
the
in
is nevertheless
fer was near perfect
practice
it"p"ii*""1 later in
tTl;:
contrary to lntask, it resultedin slight progressive
suggests'
it
important in that
ani'it
with a task
ment in the memory-scanningtask,
eip-erience
more
that
a.laiger l-uiiion'
but
early
impaiiment
generalizsmall
a
to
and
led
t"auced flexibilitv
I tne vlsuar-ur!erru''4-'-'- i""[t-h
structure
impairmenttut" ;il;;iruui-dir"rirnin^ti;n
formal
the
since
uUifitv.M-oreover,
only the
and
task.
same'
the
in oi tt " tutt remained
changed
was
The absenceof a performancechange
arrays
tli*utut
tle
of
;;,*"
t5ii"
the signal-detectioi i"rt -"V U-"au"
ffrle 2a to Figure2b' or vice
peculiarnaturerli"rii-rf.i,rchange.inthiG;a.iln
a stimulus'uui u".ru), it can be inferredihat
of the dve
configuration
iask. The spatial
dotscompriringt#r'igili-*i.'uil"r"o,
thetarget*u, ,tiri';"i;;a'r" i**r "f u'"oisistentlymovingg;;;;;-fd",.uguin*.u,ixnrr- 'p*i"rilii
domly varving bffi;;;;'"
i;rk
_ffift;bd'f"r',hh
targetdetectors
*;;iti
probab^ly
the relevantdimensionwas
ratherthan the static spatialconfigurffi;
experispecificpt""" developedthroughchange'
stimulus
the
bv
disrupted
;;; *uJ
cannotbe defiiit" "",tt"^"flnut process
but it mav be
time'
at this
;ilil;'tfl"d
discrimfigure-ground,
a
irvpJ,nrrir"athat
beconcould
targets
The
involved'
i'iutionis
complex
a
in
* figur"t embedded
;;;
background,and learnin
from ground could plal
lmprovementachievedr
this task.
A numberof other rcs
transferprocedures
in vis
ory-scanningtasks simi
ones,although in no cas
manipulationexamined
level of practice. Ross (
(1971)shiftedthe casc(
lowercase)of the chara
set after a period of pra
ported some impairmc
traineditems.Neitherstr
trol conditionin which co
servedas set members.r
nitude of the transfer ca
The apparentimplicatio
the practice-relatedimpn
partially attributablero
tive to the physicalform
In striking contrastto
boi studies,Kristofferso
(1979) reportedthat rn
perfect to new sets of t
thoseitemshad not previo
ativeor distractoritems,r
ming,and Vyas(1979)fo
fer whenonly the negativ
One characteristic
thar n
for this discrepancyis rh
negativeor distractor r
transfer in the Kristoffcn
perimentsand the samc I
Rabbitt et al. experimen
were relatively small ( iitems),it is possiblethar
diatedon the basisof eirlx
ative-s€tmembership.
Thi
supportedin the findingrh
ncre simultaneously
intrc
rtiveand negativesctsin t
rmcntand in the Maddcnr
crpcriment,a substantia,
iormanceoccurred.
Another sourceof cvid
rn thc t\pe of informatio
$xn6 from an experimcn
inn andSchneider
(1977.
:!rs srudl. groupsof items
ptrrcd together.although
srrtrre sct and sometirn
SKILLED PERFORMANCE
background,and learningto extract figures
from ground could play a major role in the
improvementachievedwith experienceon
this task.
A numberof other researchers
haveused
transferprocedures
in visual-search
or memory-scanningtasks similar to the present
ones,although in no casewas the transfer
manipulation examined at more than one
level of practice. Ross (1970) and Graboi
(1971) shiftedthe case(from uppercase
to
lowercase)of the charactersin the search
set after a period of practice, and both rcported some impairment relative to the
traineditems.Neither study includeda control conditionin which completelynewitems
servedas set members,and thus the magnitude of the transfer cannot be evaluated.
The apparentimplication, however,is that
the practice-relatedimprovementis at least
partially attributable to mechanismssensitive to the physicalform of the stimulus.
In striking contrastto the Rossand Graboi studies,Kristofferson(1977) and Prinz
(1979) reported that transfer was nearly
perfect to new sets of target items when
thoseitemshad not previouslyservedasnegativeor distractoritems,and Rabbitt, Cumming,and Vyas (1979)found perfecttransflerwhen only the negativeset was changed.
One characteristicthat may be responsible
for this discrepancyis the use of the same
negativeor distractor set in training and
transfer in the Kristoffersonand Prinz experimentsand the same positiveset in the
Rabbitt et al. experiment.Becausethe sets
were relatively small (i.e., either 4 or 8
items), it is possiblethat transfer was mediatedon the basisof either positive-or negative-setmembership.This interpretationis
supportedin the findingthat whennewitems
weresimultaneously
introducedin both positive and negativesetsin the presentexperimentand in the Maddenand Nebes(1980)
experiment,a substantialdecrementin performanceoccurred.
Another sourceof evidencefor a change
in the type of information being processed
comesfrom an experimentreportedby Shiffrin and Schneider(1977,Experiment3). In
this study,groupsof itemswere consistently
pairedtogether,althoughsometimesas the
positiveset and sometimesas the negative
t96
set. Performancewith two or four items
within the same group eventually became
indistinguishable,suggestingthat a single
categoricalrepresentationwas being used
late in practice. Salthouse(1977) reached
a similar conclusionwith different material
(nonsense
dot patterns),althoughmuch less
practicewasrequiredto establishthe generic
or categoricalrepresentationin this case.
Under the interpretationthat a singlecategorical representationmay have been establishedafter practice,the reductionin the
slope of the set-size-reaction-time
function
might be attributed to a shift in the mixture
of processingmodes from examination of
separateitem representationsto examination of a single categoricalrepresentation.
Introducingnew stimuli might eliminatethe
effectiveness
of the categoricalrepresentation and causeprocessing
to revertto specific
examination of each item representation,
thus accountingfor the significantStimulus
ChangeX Set Size interaction.
The evidencein support of practice-related improvementarising from a changein
the type of informationbeingprocessed
may
be summarizedas follows. First. it is consistent with introspectivereports from the
signal-detectionand visual-discrimination
tasks.Second,introducingnew stimuli disruptedperformancein the memory-scanning
and visual-discriminationtasks, and the
amount of disruption was greater late in
practicethan early. Third, the slopeof the
set-size-reaction-time
functionreducedwith
practice as would be expectedif subjects
were shifting to the useof a singlecategorical representationfrom multiple-item representations.
A secondclassof explanationfor practicerelatedimprovementmaintainsthat a change
in the identity or sequenceof someprocessing operationsmay be contributing to increasedperformance.There is no suggestion
of a fundamentalchangein the manner in
which the task is performedat different levels of practice in the signal-detectiontask,
as the only availableindex of such a shift,
the response
criterion usedin making signal
decisions,did not exhibit practice-related
differences.The visual-discriminationtask
also providesno indicationof a shift in the
way the task is performed with different
t9'l
L' SOMBERG
TIMOTHY A. SALTHOUSE AND BENJAMIN
At all stagesof pracamountsof experience.
tice, accuracyis poorerwhen thJtwo arrays
are presentedsimultaneorrrty,.uttt"r than
po"r* *tr*
successively,uno u""iffi"iJ
targets
contain
arrays
simultaneous
both
alsobeenreportedbv shiffrin and Schneider
(1nl ' Experimenti t and 2) and Logan
transfer
itglS',Experiment l)' In eachcase'
performance
a
in
resulted
stimuli
io familiai
it"p"itt"""t when the new assignmentof
con- 'dnl',i:o";:n"il:ffiij:i"f:"liT#,tx?
ofthearrays
th";;h"; oneorneithei
'"'+i3 j,lir?"rl;"
withsetsize,suggesting
increased
airr"ptio'n
with the memory-scanning
linkage process
sl'opeof thi that ihe stimulus-response
task is more compli;;.-il;
function decreased wasmodifiedwithpractice'
set-size-reaction-time
So-" investigators(e'g'' Neisser' 196'l)
than
with practice,but it;"r';l*";;greater
zero,andtherelationshipbetween.fuctionshaveinterpretedthepractice-relal:9^1"9,'*
slopeof the set-size-reactron-trme
;nO n"gutiu"iiials remainedcon- tion in the
i;; ;";il"
a reflectionof a shift from serial
as
i;;li";
stant across sesslons.A serial, exhaustive
is only one inio havebeen io parallel processing'This
searchprocesstherefore-seems
however'
change'
slope
the
of
teriretationemployedat all stagesLf practice.
a
invoke
might
interpretations
other
on the other hand,introducingnew stim- and
representashift from multiple to unitary
uli led to an increasein the slopeof the setiions (explainedpreviously)or an increase
be
may
""iittit
il;tit",
size-reaction-time
ln- in the reiourcesavailablefor item compara reflectionof a changein the processes
ison (see the-following)' For these reasons
volved in connectingstimuli to responses.
the siope.reductionswith practice cannot
t"1" "ti""a"i,
Not only did newrtifriii;;;
n"""ttutity be considereddefinitiveevidence
but they alsohad to f" "onn""ted to ttre api
" rrririin the-modeof processingwithin
propriate responses.rr pr"gti"g leads.to'a i"t
ltt" tuttt, althoughthey are certainly consischangein the manner-ii wtrich stimuli ar!
-- with that interpretation.
the tent
*ith ."rpJ.,.;;, ih;;;;rsing
associated
if spatially parailel processingis develarsignm"ni
customary stimulus-response^
the
op"a iittt piuiti"", one would .expect.
shouldresultin substantialp".for-un"" i-siand
ainerence between the successive
pairment. However,sincethe same stimuli
visual-discrimthe
.uttun"out conditionsin
are involved,any performun"""hung" "ould
i""ii"" i"tt to be reduced or eliminated'
stimului
of
not be attributed to disruption
This did not occur; performancewith sucencodingper se.fn" ,"."it', of the stimululcessivearray.swas consistentlybetter than
reversalmanipulation-."u""r"d that changitt"l *iitt simultaneousarrays' Neisser's
ing the assignmentof stimuli to responsEs
parallel
iiSLZl distinctionbetweenspatially
impairedp"rforman"-",unJ tn"t tt " "horrii
may be
processes
parallel
)"a "p*"1i"nally
of impairment was greater,latein practi;;
the
only
that
imporiunthere,is he suggested
than early in practicJ.Furthermor",."u".J
experience'
with
latter are d::l:l"d
interactedwith set size,causinggreatereif e c t s w i t h l a r g e r s e t s i z e s . A p o s s i b l e . i m p l i Tino support.of
s u m m a r i z e , t h e m a j o rimprovepositiveevii-rtli pi""ti"" i"a dence
9t3:ti::-Tt:ied
cation of thesefr"dil;;;
the
-"J U"ind utt.ibulubl" to a changein
to a short-circuitingof someof th" pro""rrli
operations
processing
of
identity or sequence
involved in selecting the appropriate reth" t"u"ttu1 manipulationin the
"o-"tho.
iie
sponsefor a given.-r?i-,rtur,'und^*tren
greater
task' Progressively
memory-scanning
customary urro"rutiln--oi- rii-rri and repractice
in
later
Iititptlon of peiformance
sponses*u. ,"u"rr"J'in"- "rig*"i "o.pt"i"
"""*'J uv reassigningresponsesto stimuli
Soiri
ur"a.
sequenceof proc"sr-i i;6i"
was al-io .G"in"t tn"t theionnection process
nesativetransferis apparentlyutro inuotu"al
of the
slopes
Shallower
practice'
with
teied
sin-cereversing famitiar stimuli .""*,
conalso
are
function
set-size-reaction-time
have had a larger disruptingeffectthan in-to
serial
from
shift
;iri;;i,with,a, possible
troducing comptetelynew stimuli tcr. Eigu r e s g a n d l 0 ) . p a r y l l e l p' r o c third
e s maio-r
s t n class
g ' of explanationfor
itt"
the stimu-i"u"rr"a
Resultssimilar to thesewhen
postulateda
nuJ" pru"ii""-r"tuted improvement
lus-responseurrign"*ini-i,
reduction in the procc
quired for the task wirh
experience. One means I
pretation was investigatc
ject involved the quanti
ditions in which the dur
stimulus was reduced b,
processing resources incr
then the same activitv sl
in less time or with liss
tice than early in practi
one would expect a bric
in the signal-detection a
nation tasks to caus€ m
in practice (Session8) th
(Session34). A similar a
the size reduction in thc
task. The extra resourcc
pensate for the smaller s
more available late in pr
The results of the stim
nipulation were surprisin
perlormancewas impairc
amount of impairment r
level of practice. The Ro
interaction was not signi
thus suggestingthat 26 s
did not change the subjo
with the more demanding
A second manipulatio
the processing-resources
volved the presentationof
reaction-timetask at threr
The instructionsand prc
subjects to treat the vocal
as secondary, and to atl
their maximum level of p
primary (Space Trek) ms
completely successful: st
reductionswere evident ir
tion and memory-scannin
these effects were apparcn
levelsof practice,as nonc r
'r as significant.
The results of the conc
tron-time task were consi
duced processing require
:ron. Reaction time was
lnman' task was perfon
end the amount of incrcas
r rrh more experience.Onc
o: rhese results is that altt
rcnr-rask effect (i.e.. cor
SKILLED PERFORMANCE
198
reduction in the processingresourcesre- time minus control reactiOntime
at a siven
quired for the task with greateramountsof level.ofpractice)became
smallerwith iracexperience.One meansby which this inter- tice (from 160to 102msec),it was
stilfsubpretationwasinvestigatedin the currentpro- stantial after over 40 sessions
of practice.
ject involvedthe quantitativetransfer ion- Furthermore, every
subject exhibiled this
ditions in which the duration or size of the phenomenon,as the concurrent-task
effects
stimulus was reducedby 50Vo.If available on Session45 rangedfrom 63
to 195 msec
processingresourcesincreasewith practice, acrosssubjects.
In view of the negatively
then the sameactivity shouldbe pelformed acceleratingfunction relating practice
to
in lesstime or with lesseffort later in prac- amount of reaction-timeincrease(between
tice than early in practice.In other wbrds, Sessions
5 and25 the effectreduced43 msec,
one would expect a briefer target duration but betweenSessions25 and,45 it
onlv rein the signal-detectionand visual-discrimi- duced 15 msec), one might speculate
that
nation tasks to causemore difficultv earlv many hundredsof sessions
would be necesin practice(Session8) than later in practic! sary to eliminatethe effect completely.
(Session34). A similar argumentappliesto
Another sourceof data relevantto the rethe size reduction in the memory-Jcannino sourcechangeinterpretationis available
in
task. The extra resour""r ."qui-rJO;-;;:
the set-sizecomparisonsin the memorypensatefor the smallersize are presumably scanningtask.If it is assumed
that eachadmore availablelate in practicethan early.
ditional item in the memory set requiresatThe resultsof the stimulusreductionma- tentionalcapacityor resources,
and that the
nipulation were surprisingin that although amount of these resourcesincreases
with
performancewas impaired in eachtask, tle practice,one would expect
the slopeof the
amount of impairment did not vary with set-size-reaction-time
functions to become
level of practice.The ReductionX piactice flatter with increasedpractice. In
the liminteractionwas not significantin any task, iting caseofcapacityequalto or greater
than
thus suggestingthat 26 sessions
of piactice demands,the slope should equal zero. As
did not changethe subjects'ability to cope indicatedin Figures 6 and 7, the slopes
of
with the more demandingreducedstimulus. the set-size-reaction-time
function do deA secondmanipulationusedto.examine creasewith experience,but they are
still
the processing-resources
interpretation in- about 30 msec/item ( l5 msec/item for set
volvedthe presentationof a concurrentvocal sizesof 2 to 4l on Sessions
42-45.
reaction-timetask at threepointsin practice.
A final set of dhta relevant to the proThe.instructionsand proceduresencouraged cessing-resources
interpretationof practicesubjectsto treat the vocalreaction-timetisk relatedimprovementis availablein the sucas secondary,and to attempt to maintain cessive-simultaneous
comparisonsfrom the
their maximum level of performanceon the visual-discrimination
task. If there are trulv
primary (SpaceTrek) tasks.They were not more attentionalresourcesavailable
late in
completely successful;slight performance practice,one might expectperformance
acreductionswere evidentin the signal-detec- curacy in the stimultaneous-array
condition
tion and memory-scanning
tasks.However, to becomemore similar to that in the suctheseeffectswereapparentlythe sameat all cessivearray conditionsas more attentional
levelsof practice,as noneof the interactions capacitybecomesavailable.This did not ocwas significant.
cur, as evidencedby the lack of an interThe resultsof the concurrentvocal reac- actionbetweenattentionconditionand praction-time task were consistentwith the re- tice.
duced processingrequirementsinterpretaSeveral other researchershave investition. Reaction time was greater when the gated changesin available resourceswith
primary task was performed concurrently, experienceon a task, but with greatly varyand the amountof increasebecamesmaller ing methods.Shiffrin and Schneider(1977,
with moreexperience.
One interestingaspect Experiment I ) reducedstimulus durations
of theseresultsis that althoughthe concur- from 200 to 120 msec after 1,500trials of
rent-task effect (i.e., concurrent reaction practice and reported sizable performance
199
TIMOTHY A. SALTHOUSE AND BENJAMIN L. SOMBERG
impairments,similar to those found here. other finding is consistentwith the current
The stimulusreductiononly occurredonce, resultthat the magnitudeof the concurrentand thus possiblechangesin susceptibility task effect diminisheswith practice.
The evidencewith respectto the reduced
with practiceon the originalconditionscould
interpretation of pracgenattention-demands
did
subjects
not be examined,although
is somewhatmixed.
practice
improvement
tice-related
massed
further
with
improve
erally
The reducedinterferencein the concurrent
under thesereducedconditions.
sessions
Schneiderand Shiffrin (1977:.Shiffrin & task is clearly consistentwith this view, and
Schneider,1977) also reported severalex- is not easily explainableby other interpreperiments,and discussedmany others, in tations. On the other hand, the shallower
function
which the slopesof the set-size-reaction- slopeof the set-size-reaction-time
time (or detection-accuracy)functions be- is explainableby other mechanisms,and
came very shallowwith practice.As noted practice did not lead to smaller effects of
earlier, this finding has many interpreta- reducedstimulussizeor duration,or to elimdiftions,but Shiffrin and Schneiderarguedthat ination of the successive-simultaneous
task.
it signifiesthe operationof automatic, re- ferencein the visual-discrimination
Takentogether,the current findingsalong
processes.
source-independent
with
the other results previouslyreviewed
numthe
manipulated
Theseauthorsalso
ber of elementsper display (frame size in indicate that an answerto the questionof
their terminology), and found that with what is responsiblefor improvementwith
practice,performancebecamelargely inde- practicein simple skills must take into acpendentof the number of display elements. countat leastthreesourcesof change.There
Shiffrin (1975) earliersummarizedthe re- is evidenceof changesin the type of stimulus
sults of a number of experimentsin which information being used,the identity or sediscriminationperformancewas the samein quenceof processingoperations,and in the
successiveand simultaneouspresentations. amountof processingresourcesrequired.In
Thesefindings are quite different from the the followingparagraphswe briefly describe
results,in which a compositemodelof skill improvementthat
presentvisual-discrimination
possible
target loca- incorporateseachof thesemechanisms,and
performancewith 32
remained discusshow it can accountfor the current
(simultaneous
condition)
tions
consistentlybelowthat with l6 possibletar- results.
The modelis illustratedin Figure 15. Inicondition).Stimuli
get locations(successive
(top panel) it is assumedthat protially
in the currentstudycontainedmoreelements
(i.e.,had larger frame sizes),and werephys- cessingbetweenphysicalstimulusand overt
ically larger than those used in the earlier responseoccurs in a sequenceof concepstudies,but it is not clear whether,or why, tually independentprocessingstages,each
for a differenttype of processing
thesevariablesmight be responsiblefor the responsible
(Salthouse,
l98l; Sternberg,1969, 1975)'
different results.
Logan (1978, 1979) used a concurrent- All stagesare presumedto requireattention
task procedurein which subjectsperformed (Logan, 1978) and occupytime, although
both a memory task and a reaction-time the durationsof the variousstagesmay overtask. The influenceof the memory task on lap (Eriksen & Schultz, 1979;McClelland,
reaction-timeperformancewas significantly 19'19).It is also assumedthat the encoded
smallerwith practicein two relevantexper- stimulus early in practice contains a relaiments(1978,Experimentl; 1979,Experi- tively large number of stimulus compoment I ), and slopesof the set-size-reaction- nents-many that are relevantbut alsomany
time functions in control and concurrent that are irrelevant.
It is assumedthat after moderatepractice
conditionsbecamemore similar' There was
with
the sameassignmentof stimuli to reno significantchangein the slope measure
(bottom panel),the irrelevantstimsponses
present
experin
the
with a concurrenttask
iment, perhapsbecausethe subjectshad al- ulus componentsare ignored and perhaps
of practicebe- more usefulcomponentsadded,that the enready receivedfour sessions
but Logan's codedrepresentationbecomesdirectly confore the first concurrentsession,
,"
[D']t'
E.codrnq
f" .-. ' *,"-l
Lc,'
_l
I
i
:
tmC-
Figure 15. Model for improrcrnr
panel indicates performancc scq
and bottom panel indicatcs scqr
jects. C', C2, etc., are comp(n
presentedstimulus, S, is thc cm
memory representation of thc r
decision category, and R, is rhc
of the response.)
nectedto a decisioncatcg
some processingoperat
practice),and that thc cl
mandingof attentionaln
In the caseof the pres
and visual-discriminat
sumedthat most of thc i
tributableto a changeir
encodedinformation. In
subjectshavedifficulty k
vant stimulus compone
tion and extra line, respa
ence of similar but irrc
elements(random motio
mond or X/* arrays, n
later sessionsthe enco
readily. However, at lc:
stimulusencodingappea
dependent,
sincereducin
SKILLED PERFORMANCE
d
It
d
i-
rr
n
d
rf
c
d
)f
n
)'e
IS
:n
)e
It
d
1t
i)rt
2)h
rg
).
)n
lh
rd,
:d
aly
ce
enps
nn-
200
stimulushad approximatelythe sameeffect
early, when resourceswere scarce,as late,
when processingresourceswere plentiful. It
seemslikely that this is a consequence
of the
reduceddurationsfalling in the data-limited
rather than resource-limited
segmentsof the
performance-resource
functions (Norman
& Bobrow,1975).We suspectthat thereare
probably also changesin the sequenceof
processingoperations,and possibly in the
attentiondemandsof encoding,but we have
no evidencefor this in thesetasksat the present time.
Improvementin the memory-scanning
task
is assumedto resultfrom changesin all three
major mechanisms.Stimulus encodingbecomesmore efficientby using only the minimal number of componentsrelevant for
stimulusidentification,and perhapsby shifting from establishinga representation
of the
specificstimulusto activatingthe appropriate decisioncategory.Becausethe product
of the encodingprocessis assumedto becomemore directly connectedto the appropriate response,
there is alsoa changein the
sequenceand identity of processingstages.
Figure I 5. Model for improvement of simple skills. (Top
We suggestthat the changeis more like a
panel indicates performance sequencefor naive subjects,
bypassing
of certain operations,(e.g., deand bottom panel indicates sequencefor practiced subjects. C', C:, etc., are components or features of the
tailed comparisonand decision)rather than
presentedstimulus, S; is the encoded stimulus, Mi is the
parallel processing,but we know of no evimemory representation of the stimulus, positive is the
dence yet availableto distinguishbetween
decision category, and Ri is the internal representation
thesealternatives.The attentionalresources
of the response.)
neededfor the task decreaseas variousoperations are eliminated and the encoding
nectedto a decisioncategory(thus bypassing processbecomesmore automatic,although
some processingoperationsused early in it is likely that some components,such as
practice),and that the entire task is lessde- the processof initiating a response,
continue
to requireattentionthroughoutat leastmodmandingof attentionalresources.
In the caseof the presentsignal-detection erate levelsof experience.
and visual-discriminationtasks it is preThe current experimentalfindingsare exsumedthat most of the improvementis at- plained as follows. First, the reducedslope
tributable to a changein the nature of the of the set-size-reaction-time
function with
encodedinformation. In the early sessions practice is assumedto result from the desubjectshave difficulty identifying the rele- velopmentof expandedencoding(from item
vant stimulus components(consistentmo- representation
to categoricalor decisionaction and extra line, respectively)in the pres- tivation),and from the bypassingof the comence of similar but irrelevant background parisonand decisionstages.Very fast posielements(random motion and square/dia- tive responseswith one-item set sizes are
mond or Xf 'l arrays,respectively),but in producedbecauseof a temporaryactivation
later sessionsthe encoding occurs quite of the encodingsequencefor the just prereadily. However, at least some aspect of senteditem. The fact that the slopesare
stimulusencodingappearsto be resourcein- greater than zero could be accountedfor
dependent,
sincereducingthe durationofthe eitherby a mixture of processing
modeswith
llt "-"="'""']
f**'"]
201
TIMOTHY A. SALTHOUSE AND BENJAMIN L. SOMBERG
Despiteits speculative
character
and without the comparisonstage,or by a processing?
we suggestthat the
mixture of trials with and without the acti and incompleteness,
modelillustratedin Figure 15 is a reasonable
vatedencodingsequence.
Followingthe argumentpresentedearlier, reflection of what is currently known about
the constantperformanceimpairment early the nature of improvementin simple skills.
a conandlate in practicewith a reductionof probe In that respect,therefore,it represents
stimulus size suggeststhat some aspectof temporary answerto the questionof what
the encodingprocessmay be resourcein- improvesin simpleperceptualand cognitive
dependentand data limited. Introductionof tasks.
new stimuli forcesone to engagein the slow
serial comparisonprocess,althoughthere is Adult Age Dffirences in Improvement
probablysomebenefitof prior experiencein
Before consideringthe issue of age difthe selectivityof encodingand in the connection of decision category to response. ferencesin the rate or type of improvement,
Reversingthe assignmentof stimuli to re- it is important to establishthat the current
sponsesadds the negative interferenceof samplesof long-termsubjectsare adequately
previouslyacquired"automatic" encodings representativeof their respectivepopulaand thus resultsin poorerperformancethan tions. The data in Table I and Figure 3
completelynew stimuli. As long as someof clearly demonstratethat this is the case;
the familiar stimuli are retained in their nearly all sample differences are much
we would ex- smaller than the correspondingage differoriginal responseassignments,
pect the automaticencodingto be usedand ences.It shouldbe noted,however,that the
to producebettertransferthan that obtained experimentalpopulationsin both agegroups
with all new stimuli (cf. Kristofferson,1977; are considerablyaboveaveragefor the psychometricmeasures.For example,convertPrinz, 1979:Rabbitt et al., 1979).
This model is offeredonly as a tentative ing the raw scoreson the Digit Symbol and
meansof identifyingthe major mechanisms Vocabularyteststo WAIS scaledscoresrethat seemto be involvedin the improvements vealsthat the young subjects'mean scores
found in very simpletasks.In many respects rangedfrom l3 to 16,whereasthe older subthe presentmodel is a compositeof views jects' mean scoresranged from 16 to 17.
by other theorists(e.g., LaBerge, Thesescaledscoreshavea meanof 10.0and
expressed
1973,1975; Logan,1979;Prinz, 1977,1979; a standarddeviationof 3.0 in the general
Rabbitt et al., 1979:Schneider& Shiffrin, population,and thus the presentsubjectsare
The cur- clearly in the upper rangeof the population
1977;Shiffrin & Schneider,1977).
rent formulationdiffers from any one of the with respectto psychometricmeasuresof
earlier perspectives,however,in explicitly intelligence.
The remainderof this sectioncan be oracknowledgingthe existenceof severalconceptually independent mechanisms,each ganizedin terms of three basicconclusions:
contributing to practice-relatedimprove- (a) that improvementin performanceis evment on a variety of simple tasks. Major ident in both agegroupsand is perhapseven
issuesconcerningthe relative contribution greaterin older subjectsthan in young suband time courseof each mechanismin spe- jects; (b) that sizable age differencesstill
cific tasksneedto be resolved.Thereare also remain despiteconsiderableimprovements;
detailedquestionsconcerningthe postulated and (c) that there is little evidencethat the
mechanismsthat cannot yet be answered. way subjectsperformor improvein the tasks
For example,exactly what is the nature of differs betweenyoung and old subjects.
Figures 4, 5, and 12 indicate that subthe final (asymptotic)encodingin eachtask?
increasesin performanceoccurred
stantial
Is that encodingunaffectedby the context
in which the stimulus appears?What op- in eachtask. Moreover,Age X Practiceinerationsare ignoredor bypassedafter prac- teractionswere significantin the signal-detasks,indicattice? How doesan operationbecomeinde- tectionand memory-scanning
in the
improvement
greater
absolute
ing
what
the
pendentof attention?Exactly
are
differencesbetweenautomaticand attentive older subjects.The interaction may be ar-
tifactual in the signaldc
a measurementceiling u
improvementin the ;-ou
trend in the memory-sc
data seemsunequivoca
measure,the first few ses
eral hundred trials) por
picture of the magnitud
encesevidentat later st
It is interestingto not
ments were equally ret
groups over a period of
interval causeda sligh
radation with the signa
possiblyan increasein n
action time, but no ag
significantwith any dep
Taken together,thes
cate that the acquisit
simple perceptualand r
long periodsis not impa
age. Older subjectsap
least as much as young
retain what they have k
interval just as well.
The presentresults a
with respectto the poss
practicemight lead to tt
differencesin performa
siveimprovementsin th
differencosremain in nc
performance.
One might questio
groupsof subjectsmain
motivation acrossall s
some individual differe
of enthusiasmexhibitcd
thesedid not seemcorrc
Moreover, all subject
soundsof joy or frustr
in the temporalpredict
task, suggestingthat hr
persistedat least in thir
An experimentalcho
that the older subjects
to perform at their ol
memory-scanningtask
Session48 with the offc
tivesto reducereaction
wereableto reducethci
than young subjects(5
increasingtheir error ra
SKILLED PERFORMANCE
tifactual in the signal-detection
task because
a measurementceiling was limiting further
improvementin the young subjects,but the
trend in the memory-scanning
reaction-time
data seemsunequivocal.At least with this
measure,the first few sessions
(involvingseveral hundred trials) portray an unrealistic
picture of the magnitudeof the age differencesevidentat later stagesof practice.
It is interestingto note that the improvements were equally retained by both age
groupsover a period of I mo. The inactive
interval causeda slight performancedegradation with the signal-detectiontask and
possiblyan increasein memory-scanning
reaction time, but no age interactionswere
significantwith any dependentmeasures.
Taken together,these two findings indicate that the acquisitionand retention of
simple perceptualand cognitive skills over
long periodsis not impaired with increased
age. Older subjectsappear to improve at
least as much as young subjects,and they
retain what they have learnedover a l-mo.
intervaljust as well.
The presentresults are lessencouraging
with respectto the possibilitythat extensive
practicemight lead to the eliminationof age
differencesin performance.Despiteimpressiveimprovementsin the older subjects,age
differencosremain in nearly all measuresof
performance.
One might question whether the two
groupsof subjectsmaintainedtheir levelsof
motivation acrossall sessions.There were
some individual differencesin the amount
of enthusiasmexhibitedlate in practice,but
thesedid not seemcorrelatedwith adult age.
Moreover, all subjects continued to emit
soundsof joy or frustration when engaged
in the temporalprediction(photontorpedo)
task, suggestingthat high levelsof interest
persistedat least in this task.
An experimentalcheckon the possibility
that the older subjectswere lessmotivated
to perform at their optimum level in the
memory-scanningtask was carried out on
Session48 with the offer of monetaryincentivesto reducereactiontime. Older subjects
wereable to reducetheir reactiontimes more
than young subjects(55 vs. 31 msec)while
increasingtheir error rate by aboutthe same
202
amount (57o vs. 67o). This result, in conjunction with the patternof highermemoryscanningaccuracy throughout the experiment (seeFigure 5), suggeststhat the older
subjectswere operatingwith a greater relative emphasison accuracythan were the
young subjects.The magnitudeof the age
differencesin reaction time are therefore
probablyslightly exaggerated,
but it is very
unlikely that the accuracydifferencecould
be responsible
for more than about 25 msec
of the total 135-msecreaction-timedifferencesbetweenyoung and old subjects.
. The evidenceconcerningpossibleage differencesin the mechanismsusedto perform
or improvein the tasksis somewhatdifficult
to evaluatebecauseof differencesin the absolutelevelsof performance.There were no
significantage interactionsin the signal-detectiontask. and thus there is no indication
of differentapproaches
to this task. Only an
interaction of Age X Stimulus ChangeX
Practice was significant in the visual-discrimination task. This might reflect the inability of the older subjectsto developthe
special stimulus encoding that apparently
contributedto the superiorperformanceof
the young subjects,or it might be that the
older subjectswere so closeto a floor level
in their performance that the stimuluschangeeffect could not be detected.
Severalage interactionswere significant
in the memory-scanningtask, Age X Set
Size,Age X SizeReduction,and Age X Reversal),but thesemay simply reflect a tendencyfor all effectsto be more pronounced
in the older subjects.The two age groups
appearedquite similar with respectto the
serial,exhaustivenature of the searchprocess,and the qualitativesusceptibilityto various manipulations.
The Age X Set SizeX Practiceinteraction
was also significant, indicating that the
slopesof the set-size-reaction-time
functions
becamemore similar with practice.Indeed,
on Sessions42-45 the slopesfor set sizesof
2 to 4 were nearly identical for the two
groups.
Dependingupon one's interpretation of
the set-sizeeffect,this result could indicate
that older subjects(a) developcategorical
(b) switch from serial to
representations,
203
TIMOTHY A. SALTHOUSE AND BENJAMIN L. SOMBERG
parallel processing,or (c) increase the
amount of residual resourcesto a greater
absoluteextent than young subjects.Whatever the mechanism,the current data suggestthat the two age groupsbecomealmost
equally efficient at its use late in practice,
despitepronounceddifferencesin mostother
performancemeasures.
A sizableagedifferencewasevidentin the
changewith practiceof the concurrentvocal
reaction-timeincrease,but this finding is
alsorather complicated.At face value,Figure l3 appearsto suggestthat older subjects
reducetheir secondary-taskreaction times
more, and by implicationhave a greaterincreasein the amount of their residualprocessingresourcesfrom the primary task,
than do young subjects.However,the slow
reactiontimes of the young subjectsrelative
to the old subjects,and the striking individual differencesevidentin Figure 14, suggest
that one or more artifacts may be operating
in this task. The voice-activatedrelay may
be triggeredat slightly different times after
the initiation of vocalizationin someof the
young subjects,or the attitude toward the
task may be different acrosssubjectsin the
young group. In any case,thesecharacteristics should make one cautious about attaching too much importanceto the quantitative age differences,or lack thereof,
observedin Figure 13. Practicewith a primary task may lead to a greaterincreasein
residualprocessing
capacityin oldersubjects
than in young subjects,but the presentresultsshouldnot yet be consideredstrongevidencefor this hypothesis.
We suggestthat our results,and most results on age differencesin perceptual-cognitive performance,can be explainedby assuming that older adults go through
essentiallythe same processingoperations
as youngadults,but merelyat a slowerrate.
Relativeto young subjects,older subjectsin
the currentstudyimprovedasmuch and also
retainedthat improvementover a l-mo. interval;there was alsolittle evidenceof qualitative differencesbetweenthe two groups
in the way the performanceimprovement
was achieved.The same model of performanceimprovementthereforeseemsto apply to both young and old adults.
As far as could be determined. the performance of young and old adults was qualitatively very similar, and onll' differed in
the absolute levels that were achieved. This
indicates that the cause of the age differencesis probably nonstraregic.in that there
is no evidenceof differenr approachesto the
task, and that it is unlikcll' to be experientially based, because the differences persist
over long periods of expcrience. (The lack
of experience could. however. have led to
irreversiblechangessuch thar no amount of
later experience would compensate for the
deficits. This version of thc experiential interpretation cannot be rulcd out by the present results). A fundamenral physiological
change in the nervous s!.stem therefore
seems to be responsible for these performance differences.
It appearsthat the immediate behavioral
consequenceof the age-relared physiological
change is a slower rate of processing nearly
all types of information. It is not yet clear
how such a modification in overall processing
rate might have occurred. but it is possible
that such a change could be relatively independent of the specific mechanisms used
to perform or improvc in a task. For example, consider a contrast bctween an old,
obsolete, slow computer. and a modern,
state-of-the-art, fast computer. The two machines might operatc on the same types of
infornration and even use th€ same programs
requiring approximatell' the same proportion of central processing capacity, and yet
the output would be produced much more
quickly on the faster computer than on the
slower one. Such a rate-changemechanism
in the human organism could therefore lead
to dramatic changesin the efficiency of most,
and perhaps all, types of information processing.
There are two important exceptionsto the
pattern of age differences in all performance
measuresin the present study. One is the
absence of age differences in the vocal reaction-time task (see Figure l3). As mentioned earlier, the unusual distribution of
reaction times in the ;-oung sample makes
this result suspect. However. there are other
reports of little or no age difference with
vocal, as opposed to manual. reaction times
(e.g., Nebes, 1978: E
therefore the use of e
lead to real excePtion
slowing interPretation
this issue must await fr
The second excePtlc
older subjects Performr
curately than Young sut
slopeof the set-size-re
on Sessions42-45. Par
of two through four.
preted as signifYing tha
cess,by which the Pro
ated against the men
longer time dePenden
To elaborate, considcr
earlier in which a slc
contrasted with a fast. r
types of information P
computer should requr
equivalent ProcessingI
However, if a new Pt
a hardware stimulus ,
duced into both svs
times for that Particul
longer be exPectedto I
systems.In a sense. thr
now handled bl the r
have become indePen
processing rate. Somr
this may be resPonsi
adult age differenccs
processesthat might ,
to reffect the general d
It would be desrra
dence for the proccss
of age differenccs rat
by virtue of eliminatr
natives. We are not i
alternative exPlanati
in perceptual-cogni
the current resultsind
must be incorPoratct
pretation that mrth
young and old subrol
at acquiring and rct'.
over modcratc rrnrd
are not an1 rx.txcl!
young and o5 ri5]-c
form or imPuc r: r
substantiat P{crr
in most mcasrrcr d
SKILLED PERFORMANCE
204
(e.g., Nebes, 1978; Eysenck, 1975), and responsespeedthroughout at least 50 sesthereforethe use of a vocal responsemay sionsof experience.
lead to real exceptionsto the generalized
slowinginterpretation.A firm conclusionon
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The secondexceptionto the pattern of l. Poon, L. W., Fozard, J. L., Vierck, B. A., Dailey,
B. F., Cerella, J., & Zeller,P. The efects of practice
older subjectsperformingsloweror lessacand i nformat ion feed bac k on age- re I ated dife rences
curatelythan youngsubjectsis evidentin the
in performance speed, variability, and error rates
functiohs
slopeof the set-size-reaction-time
in a two-choice decision task. Paper presented at the
meeting of the American Psychological Association,
on Sessions42-45, particularly for set sizes
Washington, D.C., September l9'l 6.
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335.
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in perBotwinick,J., & Shock,N. W. Agedifferences
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al
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xperiment
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this may be responsiblefor the absenceof
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rate
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for
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Received February 24, l98l
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