Capacity vs. bottleneck theories
• Capacity theory: minds have limited
amount of mental fuel; different tasks
share the amount of mental fuel available
- Can do two tasks in parallel, if enough mental
fuel available
• Bottleneck theory: point in information
processing where only one piece of
information processed at a time
– Serial processing  only one thing done at a
time
Simple dual-task experiment
• Have people do two very simple tasks at
the same time (2 choice RT tasks)
• E.g., task 1 = hear a tone, press a key to
signify HI or LOW pitch tone
• E.g., task 2 = see a letter, press a key
(with other hand) to signify “A” or “B”
• Can you do them at the same time?
Can’t do them at the same time
• Measure RTs: RT to one of the tasks gets
slower and slower the more the two tasks
overlap
Psychological Refractory Period
(Welford, 1967)
 Doing one task after the other
RT2
0
SOA
More on capacity theory
• Sometimes, when you try to do more than
one thing at a time, you exceed your
mental fuel (capacity), and still do tasks
just slower and less accurately
• The more capacity given to task, the faster
and more accurate your performance will
be
Capacity interpretation
• Maybe people slow down on the second
task (RT2) because they give less
capacity to that task and more to the first
task (Task 1)
Pashler (1996)
• [capacity theory developed Kahneman,
1973]
• Have people do two simple tasks
• Two tasks always happen at exactly the
same time (SOA = 0 ms)
• Measure – time between responding to
one task and responding to the other
(Inter-Response Interval or IRI)
predictions
• Bottleneck theory:
IRI
A
TASK 1
Resp
“Hi”
TASK 2
Resp
Predictions (cont.)
• Capacity theory: are doing both tasks at
the same time, just giving more energy to
one or the other
A
TASK 1
TASK 2
“Hi”
Resp
Resp
More on capacity prediction
• Will be variability in the IRIs because
people will devote varying amounts of
energy to task 1 and task 2 each time they
do it.
Results
% of
cases
0
IRI
Support bottleneck because there are no IRIs = 0
Automaticity
• Task repeated enough times where it
apparently no longer requires attention
• Driving is a good example
• Some tasks can become automatic and
others can’t
Def. of automaticity
• Memory for task is not related to whether
you’re trying to remember it
• More practice doesn’t help; hard to change
how you do the task
• Can do this task and another task at the
same time (no capacity nor bottleneck)
• Hasher & Zacks (1979)
example
• Reed text, pp. 70-1
• LaBerge & Samuels (1974)
• People did simple task with regular letters
or strange new letters
• At first, people not very good working with
new letters
• With enough practice, people are as good
with new letters as with regular letters
Selective attention
• Def.: pay attention to one thing and ignore
something else
• Cherry (1950s) created task to measure
people’s ability to do selective attention
• “Shadowing task” = to repeat a message
out loud as you hear the message (to
shadow)
Selection appears fairly complete
• Hear 2 messages simultaneously (one read to
each ear); told to repeat one and ignore the
other
• Results  people CAN do it; can shadow one
message and ignore the other
• Surprise test of what is remembered from the
other, ignored, message: none of the content, or
what language, but could tell it is a language,
and did know you heard something and gender
of speaker
When does the selection happen?
• Early processes are sensation, perception,
etc.
• Late processes start with memory,
thinking, problem-solving, etc.
• Question: Early or late selection?
Filter theory
• Broadbent (1959)
• A bottleneck theory
• We “filter” out one message based on its
early characteristics (sensation and
perception) and let the other message
through
Moray (1959)
• Cocktail party effect: trying to pay attention
to your conversation while ignoring
conversations around you
• Used shadowing technique: hearing one
message and ignoring another
• Trick: secretly place the S’s name within
the ignored message
predictions
• According to early selection, no one
should notice their name in the ignored
message (because you’re not processing
the meanings of the words)
• According to late selection, people will
hear their names (because you ARE
processing the meanings of the words)
Results
• People DO notice their names, supporting
late selection theory