(Unshadowed ear) Dichotic Listening Task. Early Findings ..

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Experimental PsychologyPSY 433

• Chapter 8
• Attention and Reaction Time

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Wheres Waldo?

• http//www.youtube.com/watch?vEvWh6PMi9Ekfeature
  player_embedded

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Two Aspects of Attention

• Divided attention what happens when we try to
  engage in two cognitive processes at once
• Selective attention how we switch mental
  resources from one cognitive task to another.

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Visible Bottleneck Task

• http//opl.apa.org/contributions/Pashler/prp.html
• This task illustrates how difficult it is to pay
  attention to two things at the same time.
• Both tasks require a choice of response and the
  same cognitive resource cannot be devoted to both
  tasks at the same time.
• The competition goes away when one task does not
  involve a choice (e.g., press any button when you
  hear a tone).

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Donders A, B C Revisited

• A is simple RT see a stimulus and press a key
• B is stimulus choice RT see one of two stimuli
  and decide whether to press a key or not
• C is stimulus and response choice RT see one of
  two stimuli and decide which of two keys to press
• B-C gives response selection time
• C-A gives ID time.

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Donders Tasks

• S1 ? R1 Donders A
• S1 ? R1 Donders BS2 ? R2
• S1 ? R1 Donders CS2

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Donders A -- Simple
A Reaction Time
C Reaction Time
C Minus A
Baseline
Identification Time
Selection Time
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Donders B -- Choice
B Reaction Time
C Reaction Time
B Minus C
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Testing for Modularity

• Donders A, B C implies that the parts of the
  task are modules.
• How can component modules be identified?
• When one component module can be changed without
  changing the others, it is independent.
• If Donders was correct then the three parts
  should be separately modifiable.
• Pure insertion addition of a module without
  affecting the duration of the other modules.

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Response Force

• Donders pure insertion could not be tested so an
  additional variable was added response force.
• Response force the amount of pressure exerted
  on a response key.
• Force increases with stimulus intensity.
• For Ulrich et al. (1999), response force was the
  same for a Donders A and B comparison, even
  though RTs were different.

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RT and Integrated Force (Fig 8.3)
This result is consistent with pure insertion.
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B and C Reactions (Fig 8.4)
The B and C RTs should differ but they do not.
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A and C Reactions (Fig 8.5)
Now RTs differ as they should but force is not
consistent with pure insertion.
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Confounding Stimulus Intensity

• Confound when one or more independent variable
  is simultaneously varied so we cant tell which
  is responsible for an effect.
• In Ulrich et al.s experiment (green LED to left
  or right), two things were varied
• Mapping of stimulus to response (one hand vs two)
• Apparent brightness (focusing on a single light
  instead of both lights)
• Replaced by letters X and S not lights.

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The Same Experiment using Letters not LED Lights
(Fig 8.6)
Now RT differs as it should and Force supports
pure insertion.
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Results using Letters

• When X vs S is used, the confound of stimulus
  intensity is eliminated (controlled) and the
  results support pure insertion.
• Part of the problem is that all three Donders
  experiments were not presented
• Authors wished to avoid transfer effects that
  occur in within-subject experiments.
• To avoid this, present all three Donders
  conditions or do the experiment between-subject.

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Speed Accuracy Tradeoffs

• RT cannot be used as the only dependent variable
  because subjects change accuracy to maximize
  speed
• Speed accuracy are sometimes inversely related.
• RT Accuracy must be jointly considered.
• Examining more than one dependent variable may be
  crucial to understanding the processes involved
  in a task.

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Theios (1973)

• Subjects had to name a digit presented visually.
• Probability of the digit was varied from 0.2 to
  0.8.
• Reaction time was unaffected by probability of
  the digit, but accuracy was greatly affected.
• Highest error rate with lowest probability.
• To increase accuracy (keep error rate constant),
  RTs would have to increase.

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RT and Error Rate as a Function of Stimulus
Probability
RT stays constant but as stimulus probability
increases, errors decrease.
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Dual Task Processing
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Speed-Accuracy Tradeoff
SOA (S1-S2 Interval in ms)
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A Central Bottleneck

• We can only process one thing at a time within a
  single modality (vision, hearing).
• Central cognition may be the most important
  bottleneck the central bottleneck.
• Whether two tasks can be done at once depends on
  whether they compete for the same resources.
• Schumacher dual-task experiment.

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Stimulus Onset Asynchrony (SOA)

• Pashler presented a modified Donders B task in
  which S1 and S2 were not presented
  simultaneously.
• The interval between them is called stimulus
  onset asynchrony (SOA)
• The shorter the SOA, the greater the effect on RT
  and errors.
• The period where one task interferes with the
  other is called psychological refractory period.

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Dual Task Processing
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Pashlers Paradigm

• Task 1 hear a tone and press a key with the
  left hand.
• Task 2 vocally call out the name of the highest
  digit in a display of eight digits.
• When subjects are not required to respond quickly
  to Task 2, accuracy is not affected.
• It only occurs with a requirement to make a
  speedy response.

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Capacity Sharing Explanation
Response selection
S1
Response selection
S2
The resource is shared during the time when the
tasks overlap.
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Explanations

• Central bottleneck models some common internal
  processing stage is required by both tasks,
  creating a bottleneck for resources.
• Central capacity sharing models a resource
  called capacity must be split across the two
  tasks, reducing the capacity available to either
  task and reducing efficiency.
• Both models predict the same observed results
  the author prefers capacity models.

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Stress and Cognitive Control

• Two possible effects of stress on cognition
• Stress requires attention (capacity) thus
  decreasing performance.
• People adapt to stress by finding more efficient
  ways of doing tasks increasing performance
  (strategies change).
• Steinhausers experiment
• Long/short interval cues to respond to digit or
  letter 6M
• Is letter a consonant/vowel, is digit odd/even?

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Results

• For the low stress condition there was an
  interaction between stimulus interval and task
  repetition (same task next or different next).
• No interaction in the high stress condition.
• Under low stress there was a relatively higher
  cost to changing tasks quickly.
• Under high stress the cost was the same.
• This is consistent with the idea that under
  stress cognitive strategies change.

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Change Blindness Demo

• http//viscog.beckman.illinois.edu/flashmovie/23.p
  hp