Martha Bridge Denckla, MD.
May 4, 2012
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Colloquial: more than one task accomplished
simultaneously
Cognitive science: more than one task between
or among which there is rapid shifting or
sequential interleaving
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In a sequence of stimulus-response tasks,
response to stimulus #1 overlaps evaluation of
stimulus #2
Reading (most obviously when aloud) involves
saying a word while “processing” the next
word to the right
Thus fluent reading involves multitasking in
the sense of interleaving
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Dual task performance does refer to
simultaneous accomplishment of two tasks
DTP is an experimental probe into R/L
hemispheric “shared processing space”
Example: Recite the alphabet while balancing a
dowel on R hand’s index finger vs. L hand’s
index finger
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Left hemisphere motor and language “shared
processing space” results in greater slow-down
of alphabet when R hand’s challenge is to
balance the dowel than when Left
Note one “habitual/automatized” (alphabet)
and one “novel” (balance dowel) task
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Each task is established “habitual/automatized”
(proverbial “walk and chew gum”)
One task is automatized, the other(s) require
online processing, with relative degrees of novelty
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Experienced driver, very familiar route, listens
to engrossing book on tape
Experienced driver, new route, misses an exit
while listening to routine newscast
Now substitute for just listening the responses
in conversation with passenger
Now conversation is on cell phone
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Motor habit, familiar visual environment,
attention-grabbing audio-linguistic. MUST
STILL REACT TO ALWAYS NOVEL
TRAFFIC!
Adding novel response formulations in
conversation, worse if passenger (or cell phone
partner) doesn’t adjust to traffic
Texting while driving adds overt shift of visual
attention plus spelling response
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Executive Function involves “I-S-I-S” and the
last 2, “Inhibit” and “Shift” are explicitly
challenged
Color-Word Subtest of Delis-Kaplan Executive
Function System
Continuous Performance Tests, including
Go/No-Go
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Diagnosis of ADHD is often associated with
cognitive control deficit (synonym for
executive dysfunction (EDF)
EDF features of inhibitory insufficiency and
inefficient (slow/variable) response
preparation are prominent if ADHD
Shifting more dysfunctional with Autistic
Spectrum Disorder than with ADHD
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Lack of efficient response preparation impairs
automaticity of one of dual tasks
Insufficient inhibition impairs allocation of
attention to novel processing demands
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Despite good/adequate acquisition of basic
skills (use of phonics, memory for sight words
with ADHD)
Reading comprehension unexpectedly lags in
many with ADHD by 4th grade
Suspect “processing speed” issue complicated
by working memory deficit
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Analysis of Processing Speed and Working
Memory in Experimental tasks
fMRI of Working Memory
aMRI/DTI of relevant brain connectivity
Electrophysiology of Multitasking
Joshua Ewen, MD
Kennedy Krieger Institute/JHUSOM
Spectrum 2012
ewen@kennedykrieger.org
KKI CSRD
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Martha Denckla
Mark Mahone
Matthew Ryan
Lisa Ferenc
Priya Xavier
JHU Psychological and
Brain Sciences
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Howard Egeth
Jeff Moher
KKI Clinical Neurophysiology Laboratory
• Balaji Lakshmanan
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Reading Fluency
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Conversation
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Sports, Video Games
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Driving
S
R
S
S
Visual
Proc
“Cognitive Processing”
Stimulus Eval
Response Sel
RT
R
Response Exec
R
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Well described
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Reaction time (RT) tasks
 Wodka et al, JCEN 2007
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Oculomotor tasks
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Thaler et al, J Atten Disord 2011
Nielsen & Wiig, Int J Psychiatry Clin Pract 2011.
Mahone et al, JAACAP 2009
Hynd et al, J Learn Disabil 1989
Clinical Measures
 WISC-IV PSI (Coding and Symbol Search)
 Mayes & Calhoun, J Atten Disord 2006
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Reading Fluency
 Ghelani et al, Dyslexia 2004
 Willcutt et al, Am J Med Gen B 2007
S
Visual
Proc
Stimulus Eval
Response Sel
Response Exec
RT
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Response Execution (i.e., motor)
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Doesn’t explain silent reading fluency
Stimulus Evaluation vs. Response Selection
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“input-side” vs. “output side”
R
S
Visual
Proc
Stimulus Eval
?
Response Sel
RT
Response Exec
R
T1
T2
Stimulus Onset Asynchrony (SOA)
Visual
Proc
Stimulus Eval
Visual
Proc
Visual
Proc
Stimulus Eval
Visual
Proc
Response Sel
Stimulus Eval
Response Sel
Stimulus Eval
RE
Response Sel
RE
Response Sel
RE
RE
Visual
Proc
Stimulus Eval
Response Sel
RE
Long SOA
Short SOA
Visual
Proc
Stimulus Eval
Response Sel
RE
Marois & Ivanoff, Trends in Cog Sci 2005
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“Central processing bottleneck”
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Amodal
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Some evidence for
subcortical contribution
 Ivry et al, J Exp Psychol: Hum
Percept Perform 1998
 Pashler er al, Neuroreport 1994
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Multiple frontal areas
 Marti et al, NeuroImage 2012
 Marois et al, Psychol Res 2006
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Frontal-Parietal Networks
 Hesselmann et al, NeuroImage
2011
Visual
Proc
Stimulus Eval
Visual
Proc
Visual
Proc
Stimulus Eval
Stimulus Eval
Visual
Proc
Response Sel
Response Sel
Stimulus Eval
RE
Response Sel
RE
RE
Response Sel
RE
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44 children (19 ADHD, 25 control), grades 4-8
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Evaluated PRP effect
F(1,34) = 3.97, p = 0.05; ηp² = 0.11
Ewen et al, Dev Neuropsychol 2012
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Conclusions:
Kids with ADHD have a higher cost
for multi-tasking
2. This cost manifests in processing
speed
3. This cost represents slowed response
selection
1.
S
Visual
Proc
?
Stimulus Eval
Response Sel
RT
Response Exec
R
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Parietal association cortex
 Picton, J Clinical Neurophysiol 1992
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Combined in PRP-inducing paradigm, inferior
parietal—pre-central regions activate
 Hesselmann et al, NeuroImage 2011
Luck, Psychol Bulletin 1998
1.
No significant effect of diagnosis on P3 latency
2.
P3 and PRP reasonably independent:
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3.
P3 latency predicted only 6% of PRP results
PRP (plus P3) predict reading fluency
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ΔR2 = 0.27
Majority of the effect from PRP
ADHD showed stronger PRP-fluency effect than
controls
1.
2.
3.
Children with ADHD have slowed processing
speed
Motor slowing is not a confound in some
measures
Response Selection is slowed in ADHD
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4.
Increased costs for multi-tasking
Relationship to fluency
Stimulus Evaluation may be slowed, but perhaps
not a key contributor
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P50 HD052121 (MBD; EMM)
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K12 NS001696 (H. Singer)
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K23 NS073626 (JBE)
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Johns Hopkins ICTR
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KKI IDDRC
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Multitasking involved in reading
comprehension is inefficient with ADHD
Recapitulation: Fluency facilitates
comprehension and itself depends on
interleaving sequential response preparation
with overlapping stimulus evaluation
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On scale of hours, switching and interleaving
several strands of life
School (4-5 subjects)/Extracurricular/Home
Work (might be subdivided)/Family
“Covert” multitasking from middle school
through life involves “cold” and “hot”
cognition (skills/duties vs. social relations)
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Holding/bouncing baby, stirring pot of soup,
talking on phone to patient
Dictating patients’ reports while sitting in car
during sons’ soccer practices
Switching between patient reports and portions
of research papers to meet deadlines of others
to whom “owe” work
Note necessity of Working Memory to a
multitasking agenda