3 – Selective Attention
selective attention
attending to part of the environment while ignoring the rest
Examples
Listening to instructor while ignoring everything else
Looking around a room for the face of your friend
Spotlight Metaphor
We must limit the scope of our attention because “attentional resources” are limited
Example
basketball pass demo (1:22)
www.dansimons.com/videos.html (videos 1 and 2)
or www.youtube.com/watch?v=vJG698U2Mvo
Inattentional Blindness
failure to notice salient object even if looking directly at it.
Experiment
Ss watched video of people passing basketballs.
Ss told to count passes.
About 50% of Ss didn’t notice gorilla.
(Simons & Chabris, 2001)
Real world example
Car driver makes left turn without noticing oncoming motorcycle.
Note that unnoticed object is
1) not expected
2) not looked for
Radiologists were shown this lung scan and asked to look for “cancer nodule”
83% failed to notice
Drew and Wolfe (201X)
blank
Change Blindness
failure to notice change in object while it is briefly out of view
Person-Swap Experiment
S entered laboratory to participate in study and meets E.
E surreptitiously traded places with different E.
Some Ss didn’t notice.
Note the distinction:
inattentional blindness
Not noticing object
change blindness
Not noticing change in object (or scene)
Videos with Demos
Person-Swap in lab (3:59) www.youtube.com/watch?v=38XO7ac9eSs&feature=related
More demos (2:10, 1:17) www.dansimons.com/videos.html (first panel, videos 3 and 4)
Dan Simons
Another Person-Swap Experiment
E asks S for directions.
S begins to give directions.
While E briefly out of view, E covertly trades places with another E.
About 50% of Ss didn’t notice.
(Simons & Levin, 1998)
video (1:36)
www.dansimons.com/videos.html second panel, video 1
Flicker task demo (photos from Rensink et al., 1997)
animation
Flicker task demo (photos from Rensink et al., 1997)
use cursor keys: R…R, R, L, L, R, R, L, L,
Flicker task demo (photos from Hollingworth, Schrock, & Henderson, 2001)
use cursor keys: R…R, R, L, L, R, R, L, L,
Flicker task demo (photos from Rensink et al., 1997)
use cursor keys: R…R, R, L, L, R, R, L, L,
Flicker Effect
1. S sees scene, brief blank screen, and then altered version of scene
brief
blank screen
2. Alternations continue (“flickers”) until S identifies change
3. S is told to find the change
4. Finding the change takes a long time (flicker effect)
Note: the flicker effect is a kind of change blindness
Demos
www2.psych.ubc.ca/~rensink/flicker/download/indeT.html
Flicker Effect Experiment
Original and altered scenes scene alternated until S identified the change
blank screen
240 ms
blank screen
X ms
240 ms
X ms
Duration of blank screen = 0 or 80 ms
Results
Blank Duration
Mean # of Alternations
0
1
(no change blindness)
80 ms
16 (change blindness)
Conclusions
Change blindness occurs if scene must be stored in memory - even for a moment.
Thus, we can store only a very brief amount of the information in a visual scene
(Rensink et al., 1997)
no gap demo nivea.psycho.univ-paris5.fr/ECS/bagchangeNoflick.gif
Attentional Capture
Noticing a sudden change in object (or part of scene) to which you are not attending
Stimuli that capture attention
Flicker Task without intervening blank screen
Scream
Siren
Ringing phone
Brake lights on the car in front of you
Some changes capture attention better than others.
Change in Stimulus
Efficacy
Example
Increased intensity
okay
Tail lights get brighter.
Onset
good
Rear window light turns on.
Repeated onset-offset
better
Brake lights flash.
Example.
On some cars,
brake lights flash if speed > 50 km /hr
500sec.com/adaptive-brake-light/
Resisting Attentional Capture
In most situations, attentional capture is adaptive
While walking in woods, we notice snake in our path.
Air traffic controller notices flashing red light
In some situations, we must be able to resist attentional capture.
Example
School bus driver must ignore yelling kids
Student taking test must ignore coughs, door slams, etc.
Naturally, people vary in the ability to resist attentional capture
Experiment : Resisting Attentional Capture
Ss told to look at cross (+) and ignore intermittently flashing circles.
Square appeared in top or bottom location. (This repeated many times)
Ss pressed top or bottom key, respectively.
Results: ADHD kids made far more errors than controls did.
Implication: ADHD kids have a hard time resisting attentional capture.
(Bourel-Ponchel et al., 2010)
Right Ear
In 1913 Danish physicist Neils Bohr’s eponymous Model postulated
atoms were formed of electrons orbiting a nucleus, much like planets
around the sun – only using electrostatic attraction rather than gravity.
Electrons have since been shown to be more akin to waves surrounding
the nucleus, but teams in Austria and the US have shown they can be
made to perform in the same way as planetary systems, and the
technique can be used to change the overall size of the atom.
The research, published in the journal Physical Review Letters was
inspired in part by the function of Jupiter’s Lagrange points: Two specific
points where forces of the Sun and the largest planetary gravity well in
the Solar System cancel each other out. These collect matter, known as
the Trojans, and the best guess is that the two belts contain more than a
million asteroids over a kilometer in diameter.
A team at the Vienna University of Technology performed the
mathematics for the experiment and Rice University performed the
actual experiment. They fired an atomic beam through a vacuum
chamber and then crossed the stream with a tuned laser oscillating with
the orbital period frequency of the electron around the nucleus.
The laser created a localized electronic state that moves in a nearcircular orbit around the nucleus, and they could then extend and
reduce the size of the orbit by modulating the laser’s frequency. The
team got an atom up to the size of a human blood cell during testing.
The electron can only be controlled when the force is applied and then
reverts to its natural state within a few cycles. Then again, Jupiter is not
perfect either. Simulations suggest 17 per cent of the Trojans are
unstable enough to fall out of the orbits and go wandering, potentially
Earthward bound.
The next step is to see if the technique can be used on multiple atoms
simultaneously, and to monitor how they interact with each other during
operations.
Sandwiched between venerable classical physics and the extremes of
quantum studies, mesoscopic physics is very much the red-headed
stepchild of the physical sciences, but has huge potential. It generally
deals with objects from an atom up to 1,000 nanometers – about the
size of the average bacterium. By investigating the boundaries between
the sub-atomic quantum world and everyday physics, mesoscopic
scientists hope to find usable results that could have applications in both
fields.
Left Ear
A team of scientists have discovered over 40 new species in
southwestern Suriname survey.
The team performed a three-week survey in three remote sites
along the Kutari and Sipaliwini Rivers.
“The goal of this expedition was to bring together the knowledge
and expertise of local people with scientific knowledge to study
and plan for monitoring of biological and cultural resources of the
region.” The scientists surveyed a total of 1,300 species,
including 400 plants, 90 aquatic beetles, 90 dung beetles, 76
katydids, 93 dragonflies and damselflies, 100 fishes, 57 reptiles
and amphibians, 323 birds, 41 small mammals, 29 medium and
large mammals.
They also saw 14 threatened species of plants and animals that
are listed on the International Union for Conservation of Nature’s
Red List.
Part of the list of new species includes a “cowboy frog” and a
spiked species of armored catfish.
The cowboy frog has white fringes along the legs, and a spur on
the “heel.”
The armored catfish has external bony plates and is covered with
spines to help defend itself from giant piranhas.
The researchers said that one of the local guides was about to
eat the armored catfish as a snack, until scientists noticed its
unique characteristics and preserved it.
The team also found a “Great Horned Beetle” on their
expedition. This beetle is “the size of a tangerine” and weighs
over 0.2 ounces. It is metallic blue and purple, and posses a
horn on its head used as a weapon to fight in battle.
“The area was paradise for the entomologists among us, with
spectacular and unique insects everywhere. I didn’t even have to
look for ants because they jumped out at me”, Dr. Leeanne
Alonso, a former CI RAP Director who is now with Global Wildlife
Conservation, said in a press release.
Right Ear
Left Ear
scooter
mission
amplitude
kitchen
genre
selection
maroon
double
expression
bucketful
neurology
intersect
apparent
defective
treatable
orangutan
qualitative
illusion
totem pole
dangle
charging
trample
mansion
revision
bluebird
streaky
famous
remover
uplifting
sought
perpetuate
crouch
veritable
deflect
foray
cape
redundancy
transposition
capability
geese
accentuate
spectacular
gargantuan
heading
pivot
humanist
mainsail
collectible
xylophone
collection
penetrate
alphabetical
teacup
sarcophagus
moonlight
formulation
motif
bondage
furthermore
integration
overrun
cohabit
exhortation
envoy
widen
platitude
opulence
uncover
ruckus
difficulty
inhabit
cafeteria
intellectual
induction
ammonia
reindeer
wrench
sidetrack
biology
instance
Dichotic Listening Procedure
S hears words in one ear while simultaneously hearing different words in other ear.
S is told “left” or “right” and then attends to the message in that ear.
S repeats attended message aloud (shadow)
Trial continues for 10-60 s.
Then, S is asked about unattended message.
Dichotic Listening Experiment
S heard prose in one ear; word list in other ear. Subjects shadowed the prose.
It was the best of times,
it was the worst of times.
dog, wall, green, bell,
anger, wish, tiger, sky,
Immediately afterwards, S asked about unattended message
Results: Ss can say unattended words were English
But Ss couldn’t recall any of the words!
This was true even if the list included the same word 35 times in a row!
Conclusion
Our mind does not “process” the meaning of unattended message.
(e.g., Broadbent, 1957; Cherry, 1953; Moray, 1959)
Early dichotic listening studies suggest that we can process only one message at a time.
However, we know that this is not entirely true.
Example
cocktail party effect - we notice our name used in nearby unattended conversation
Might our minds process information other than our name, without our awareness?
Dichotic Listening Experiment 2
Ss heard two stories, one in each ear.
After 20-30 s, and without warning, the stories unexpectedly switched ears.
The fox chased
[switch]
skipping rope
I saw the girl
[switch]
big gray rabbit
Results
After switch, Ss often shadowed wrong prose because it made sense.
“I saw the girl skipping, er, big gray rabbit …”
Conclusion
Ss understood the meaning of the unattended message!
(Treisman, 1960)
Since then, 1000s of follow-up studies have been done.
Most researchers believe we can “partly” process meaning of unattended message.
Neglect disorder in which patient “ignores” objects in left or right visual field.
Example
Patient asked to copy model on left.
Patient’s drawing is shown on right.
Facts about neglect
Left neglect is far more common than right neglect.
Common symptoms
Leave one shoe off
Leave food on one side of plate
Shave one half of face
Patients notice object on left side if they turn all the way around to the right.
Video
Patient draws daisies (3:19) www.youtube.com/watch?v=ymKvS0XsM4w
(Bisiach, 1996)
(McCarley et al., 2004)
Visual Search
search for an object within a visual scene
Examples
Looking for car in crowded parking lot
Finding certain brand of cereal on grocery story shelf
Airport worker looking for knife in luggage scan
(Image from McCarley et al., 2004)
Typical Visual Search Experiment
S told what the target is.
Computer screen shows one target and 1 – 50 distractors.
S presses yes-key if target is there, no-key if target is not.
E measures RT.
Examples
Find the I
L
I
1 distractor
(Treisman & Souther, 1985; Wolfe, 2001)
Find the I
L L L L
LL L L
L L L L
L L LL
L IL L L
L L L
L
L L L L L
L L L LL
L
L L
L LL L L L
L L L
L
L L L
50 distractors
Find I among Ls
L L
L
L
L
L
L L L
L
L L L
L L
IL L
L
L
L
LL L
L
L
L L L L
L L
L
L
L L
L L
L L L L
L L
L
L L
L
L L L L
Find I among Ls (again)
L
L
L L
L
L L
L L
L L L L L
L L L L
L
L
L L L
L L
L
L
L
L
L
L
L L L
L L L
L L
L L
L L
L L L L
L
I L
L
L L
L
L
L L
Find I among Ls (again)
L L
L
L
L
L L L
L
L L L L
L L L
L L
L
L
L L
L
L
L
L L
L L
L
L L
L L
L L
LL
L
L
L
L
L
L
L
Find I among Ls (again)
I
L
Find I among Ls (again)
L
L L
L L
L
L L
L
L
L
L
L L
L
L L
L
L
L
L
L
L
L
L
LL
L
L
L
L
L
I
L L
L L L
LL
L
L L
L
L
Find P among Bs
B B
B
B
B
B
B B B
B
B B B
B B
B B
B
B
B
BB
B
B
B
B B B B
B B
B
B P B B
B B B B B B
B B
B
B B B
B B B B
Find P among Bs (again)
B
B
B B
B
B B
B B
B B B B B
B B PB B
B
B
B B B
B B
B
B
B
B
B
B
B B
B
B B B
B B
B B
B B
B B B B
B
B B
BB B B
B
B B
Find P among Bs (again)
B B
B
B B
B
B B
B B
B
B
B B
B
B B
B
B B B
B B B B
B
B B
B
B B
B
B B
B
B BB
B
B
B
B
B
B
B
Find P among Bs (again)
B
B B
B B
B
B B
B
B
B
B
B B
B
B
B
B
B
B
B B
BB
B
B
B
B B
B
B
B
B
P
B B
B B B
BB
B
B B
B
Do all searches take longer when more distractors are added?
Find T among Ts
TT T
T T
T T
T
T T T
T
T
T
T
T
T
T T
T
T T
T T
T T T
T
T T
T T
T
T
T
T
T
T
T
T
T T
T
T T
T T T
TT
T T
Find  among  s









 



 

 






 
  
 


Can a target pop out if it’s the same color as the distractors?
Find X among Os
O O
O O
O
O
O
O
O
O
O X
O
O O
O
O
O
O
O
OO
O
O
O
O O
O
OO
O
O
O
O
O
O O
O
O
O
O
O
O O
O
O O
Find X among Os (again)
O
X
Find X among Os (again)
O O
O O
O
O
O
O
O
O
O
O
O O
O
O
O
O
O
OO
O
O
O
O O
O
OO
O
O
O
O
O
O O
O
O
O
O
O
O O
O
O O
Find | among 


    
 |

  
  


  

   
    

     
Two kinds of visual searches
pop-out RT unaffected by more distractors serial RT increases with more distractors
(as if checking all items at once)
(as if checking one object at a time)
Find P among Bs
Find X
Find BP
B B
B
B
B
B
B
B
B
B
B B B
B B B
B B
B
BB
B
B
B B B B
B B
B
B P B B
B B B B B B
B B
B
B B B
B B B B
B
RT
RT
30 ms
1 item
# of distractors
# of distractors
slope  0
slope  30 ms / item
Thus, all items are checked “instantly”
Thus, 30 ms = average time to check
Theoretical interpretation
Pop-out search is
Serial search is
pre-attentional
attentional
1) automatic
1) volitional
2) nearly unlimited capacity
2) very limited capacity
The big question:
What determines whether a target pops-out (i.e., is found without attention)?
Find O among Qs
Q Q Q Q
QQ
Q Q Q Q
Q Q Q Q
Q
Q Q Q
Q
OQQ Q Q Q Q Q Q
Q Q
Q
Q Q
QQ
Q Q
Q
Q Q Q
Q
Q QQ
Find O among Qs (again)
Q Q
Q
Q Q
QQ
Q Q
Q Q
QQ
Q Q
Q
Q Q
Q
Q
Q
Q Q Q O Q Q Q
Q
Q
QQ
QQ
QQ Q
Q Q
Q
Find O among Qs (again)
Q
QQ Q Q
Q
QQ
Q
Q QQ Q
Q
QQ
Q
Q Q Q
Q
QQ
Q
Q QQ
Q Q Q
Q Q Q Q
O Q Q Q Q Q Q QQ
Find O among Qs (again)
Q Q Q Q
QQ
Q Q Q Q
Q Q Q Q
Q
Q Q Q
Q
QQ Q Q Q Q Q Q
Q Q
Q
Q Q
QQ
Q Q
Q
Q Q Q
Q
Q QQ
Find O among Qs (again)
Q
O
What if we switch target and distractors?
O among Qs  serial
What about Q among Os?
Find Q among Os
O O O
O
O
OO O
O O
OO O O
OO
O O O
O O O
O O
O O O O O O OO O
O O O O OO
OO
OO O O O
OO Q
O
Find Q among Os (again)
O O O O
O O O
OO O O
O Q O
O O O OO O
O
O O
O O O O O
O OO O O O O O
O
O O O O O O
OO O
O O
O
O O
O O
O O
Summary
X among Os
pop-out
| among s
pop-out
O among Qs
Q among Os
serial
pop-out
Hypothesis?
feature-presence search
You can simply look for presence of a distinguishing feature
Always pop-out
Examples
Search for object with black color
Search for object with X-shape
Search for object with vertical orientation
feature-absence search
You must look for absence of distinguishing feature
Always serial
Examples
Must search for object without horizontal line
Find P among Bs
B B
B
B
B
B
B B B
B
B B B
B B
B B
B
B
B
BB
B
B
B
B B B B
B B
B
B P B B
B B B B B B
B B
B
B B B
B B B B
Must search for object without double hump
Must search for object without vertical line
What if search has two kinds of distractors?
Find X among Ts and Os
T T O T O T T O O T
O T O O T O T O O T
T O O T O O T O T O
O T O O T T O X O T
O O T T O T O T O O
T T O T O T O O T T
Find T among Ts and Os
T T O T O T T O O T
O T O O T O T O O T
T O O T O O T O T O
O T O O T T O T O T
O O T T O T O T O O
T T O T O T O O T T
T among Ts and Os  pop-out
What about T among Ts and Os ?
T among Ts  pop-out
T among Os  pop-out
Find T among Ts and Os
T T O T O T T O O T
O T O O T O T O O T
T O O T O O T O T O
O T O O T T T T O T
O O T T O T O T O O
T T O T O T O O T T
Find T among Ts and Os (again)
T T O T O T T O O T
T T O O T O T O O T
T O O T O O T O T O
O T O O T T O T O T
O O T T O T O T O O
T T O T O T O O T T
Find T among Ts and Os (again)
T T O T
O TO
TO
O T
O TO
O T O O
O O
T TO
O T
T
OOT
O TO O
O T O T
T T O
O T O
O
T O T
T T O T O T
T
T
T O
OT
T
Find
among
s and
s
Find  among s and s
Find O among Os and Ns and Ns
feature conjunction search You must look for presence of two distinguishing features
Always serial
Example
Find
Must find object that is black AND vertical
-------Note distinction:
Target can be found by looking for object with one distinguishing feature  pop-out
Target can be found only by looking for object with two distinguishing features  serial
Overview of Demonstrations
target
distractors
distinguishing
feature
kind of
search
result
I
L
horizontal bar
absence
serial
X
O
X shape
presence
pop-out
red X
blue X
red
presence
pop-out
|

vertical-ness
presence
pop-out
Q
O
hook
presence
pop-out
O
Q
hook
absence
serial
red X
blue T, green O
red or X-shape
presence
pop-out
red T
blue T, green O
red
presence
pop-out
red T
blue T, red O
red and T -shape
conjunction
serial
Which search produces pop-out, if either?
O among Cs
C among Os
Find O among Cs
C
C C C C C C C
C
C C C C C
C C C C
C C
C C C C C C C
C C C
C C C C C C
C C C C
C C O C C
C C C
C C C C
CC
C C
C CC
C C C C
Find O among Cs (again)
C
C C C C C OC
C
C C C
C C C C C C
C C C C
C C C C C
C C C
C C C C
CC
C C
C CC
C C C C
C C C C C
C C C C
C C
C C C C C C C
Find O among Cs (again)
C C
C
C
C C C C
C
C
C C C C C C C
C
C C C C C
C C C C
C C C C
C C O C C
C C
C C C C C C C
C C C
C C C C
CC
Find C among Os
O O O O O O O O
O
O O O O O
O O O O
O C O O O O O O O
O O O
O O O O O O
O O O O
O O O O O
O O O
O O O O
OO
O O O OO
O O O O
Find C among Os (again)
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O O O O O O
O O O
O O O O
O O O O O O O
O O
O O O O O
O
O O O C
OO
O O O O O O
O
O OO
O O O O
Find C among Os (again)
O O O
O O O O O O
O O O
O O O O
OO
O O O OO
O O O O
O O O O
O O O O O
O O O O O O O C
O
O O O O O
O O O O
O O O O O O O O O
C among Os
pop-out
O among Cs
serial
Find
Find
More Asymmetries
Kristjansson & Tse (2001)
A different kind of asymmetry
pop-out
Enns & Rensink (1991)
serial
Search Asymmetries
In some cases, swapping target and distractors changes search from serial to pop-out
(e.g., Wolfe, 2001)
With complex targets, RT slopes are steep
Find
Find “square”
Find normal face
Other questions…
Is a slow search even slower if distractors are not known in advance?
Find X
vs.
Find X among Xs and Os
Is feature-present search slower if there are many kinds of distractors?
Find T among Ts and Ts
vs.
Find T among Ts, Ts, Ts, Ts, Ts, and Ts
Still more searches
Find
Find
(e.g., Li et al., 2008; Pinto et al., 2010, Wolfe, 2003; 2005)
Practice Questions
target
distractors
distinguishing
feature
kind of
search
result
red T
blue T
red
presence
pop-out
red 
red |
horizontal orientation presence
pop-out
red T
blue O
red or T
presence
pop-out
blue T
red T, blue O
blue and T
conjunction
serial
red T
green T, blue O
red
presence
pop-out
Target = BLUE Q. Search is serial. Identify distractors.
A. red Qs
B. blue Os
C. blue Ts, red Qs
Target = GREEN O, Search is serial. Identify distractors.
A. red Os
B. green Qs
C. red Ts, blue Os
C
D. red Ts, green Qs
B
D. red Qs, blue Os
More Practice Questions
If one looks for a green I among green Ls, what kind of search is it?
A. feature presence
B. feature absence
C. feature conjunction
If one looks for a blue O among red Os and green Ts, what kind of search is it?
A. feature presence
B. feature absence
B. feature absence
B. feature absence
C
C. feature conjunction
If RT is unaffected by the number of distractors, what kind of search is it?
A. feature presence
A
C. feature conjunction
If one looks for a blue O among red Os and blue Ts, what kind of search is it?
A. feature presence
B
A
C. feature conjunction
The End
gorilla study based on earlier study by Neisser and Becklen (1975)
Dichotic listening studies (and 1000s of other studies) have led to two camps.
early selection theory
Early on, one message must be selected for processing of meaning.
Sample Evidence: Ss who didn’t notice “monsoon.”
late selection theory
Both messages can be partly processed before one must be selected.
Sample Evidence: Ss who shadowed wrong message after switch.
Truth is a complicated hybrid of two theories.
Unattended message processed “to some degree.”
Rancorous debate continues.
Selective Attention
attending to part of the environment while ignoring the rest
Examples
Reading a book while ignoring extraneous noise
Selective Attention Demo.
First read the bold text. Then read the italicized text.
The Every fact man that gets some a geniuses narrower were and laughed narrower
at field does of not knowledge imply in that which all he who must are be laughed an
at expert are in geniuses. order They to laughed compete at with Columbus, other
they people. laughed The at specialist Fulton, knows they more laughed and at more
the about Wright less brothers. and But less they and also finally laughed knows at
everything Bozo about the nothing. Clown.
Konrad Carl Lorenz Sagan
The ability to “selective attend” varies across individuals.
Example
Classroom noise affects test scores of some people more than others.
Selective attention ability predicts performance on some tasks.
Correlational Study
E measured selective attention of fighter pilots (using auditory task).
Selective attention scores predicted flying skill (even though flying is visual).
However, ability to selectively attend might impair performance on some tasks.
(Carretta et al., 1976; Gopher & Kahneman, 1971; Mihal & Barett, 1976)
Everyone knows what attention is.
(James, 1890)
A formal definition of the term “attention” is not presently available…
(Pashler & Johnston, 1998)
Since 9/11 attacks, government has funded studies of visual search of luggage
Sample ETperiment
Ss see many luggage scans.
1 in 5 scans include knife.
Knife shape and orientation vary.
Ss “stop bag” if they see knife.
Results
Practice improves performance only if target similar to recently seen targets
Conclusion
Practice might not improve performance.
(e.g., McCarley et al., 2004; 2010)
Find E among Fs
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
F F F F F F E F F F
Find E among Fs (again)
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
F E F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
Find E among Fs (again)
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
Find E among Fs (again)
F F F F F F F F F F
F F F F F F F F E F
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
Find E among Fs (again)
F
E
Find E among Fs (again)
F F F F F F F F F F
F F F F F F F F E F
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
F F F F F F F F F F
What if we switch target and distractors?
Find F among Es
Find F among Es
E E E E E E E E E E
E E E E E E E E E E
E E E E E E E E E E
E E E E E E E E E E
E E E E E E F E E E
E E E E E E E E E E
Find F among Es (again)
E E E E E E E E E E
E E E E E E E E E E
E E E E E E E E E E
E E E E E E E E E E
E E E E E E E E E E
E F E E E E E E E E
Find F among Es (again)
E
E
F
Interpreting slope when visual search is serial
ETample
slope = 40 ms / eTtra item
Thus, it takes 40 ms to scan each item (on average)
RT
40 ms
1 item
# of distractors
Two kinds of visual searches
Slow
RT increases with more distractors
Fast
RT unaffected by more distractors
Find Find
P P among Bs
B B
B
B
B
Find T
B
B B B
B
B B B
B B
B B
B
B
B
BB
B
B
B
B B B B
B B
B
B P B B
B B B B B B
B B
B
B B B
B B B B
RT
RT
# of distractors
slope = rise / run = 40 ms/ item
slope = average amount of time to check each item
# of distractors
Some ugly technicalities.
1. Sometimes, serial search is few items at a time, not one a time.
2. With parallel pop-out, slope is not quite zero but still very small.
We will ignore the above.
The important question: what determines whether search is serial or parallel?
Summary of Results: 3 kinds of visual search
feature presence  fast
target has at least one distinguishing feature
T among Os
Q among Os
red T among blue Ts, green Os
feature absence  slow
can find target only by finding the object without distinguishing feature
O among Qs
feature conjunction  slow
can find target by looking for object with at least two distinguishing features
red T among blue Ts, red Os