Chapter 3

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Nov 14, 2013 (3 years and 9 months ago)

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Cognitive Processes

PSY 334

Chapter 3


Attention

What is Attention?


Attention is the allocation of limited
processing resources.


Visual features such as shape, color,
texture, motion are processed in parallel.


Serial bottleneck



occurs when it is no
longer possible to process in parallel.


When does it occur


early vs late
selection


How do we select what to attend to?

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).

How we Experience Attention


Stream of consciousness
--

we learn and
remember what we attend to.


Paying attention results in a feeling of
mental effort.


Can be directed internally but also pulled
(attracted) by external events.


Varies with arousal and fatigue.


Studied by looking at response
competition.

Auditory Attention


The response competition comes from
having two ears.


Dichotic listening

task


uses

shadowing
.”


Two different messages are presented,
one to each ear. Subjects are asked to
speak what they hear.


People can attend to only one message at
a time.

Auditory Shadowing

Broadbent’s Filter Theory


People do not remember the content of
the unattended ear.


Voice or noise, sex, but little else.


Broadbent’s
filter theory

proposed that
filtering occurs early in processing based
on physical characteristics (pitch, ear).


Neural evidence supports the ability to
select one ear to listen to.


Cocktail party effect



attention switches
based on content of unattended ear.

Broadbent’s Early Selection

Only the selected information
gets through.

Gray & Weddeburn’s Study

Subjects can successfully shadow
a message that jumps back and
forth between ears.


This means that people can
shadow based on meaning, not
just physical characteristics.

Treisman’s Attenuation Theory


Treisman’s
attenuation theory



subjects
deemphasize but not filter out the
unattended message.


Meaning switched from one ear to the
other.


Some subjects switch ears even when told
not to, following the semantic content.


Semantic criteria apply to all messages,
filtered or not.


Treisman’s Attentuation
Theory

All information passes
through but some is weaker
(attenuated).

Late Selection Theory


Deutsch & Deutsch’s
late selection
theory



the limitation is in the response
system, not the perception.


Both messages are perceived in terms of
meaning, but only one can be shadowed at
a time.


The criterion for selecting what to say can
change


based on ear or meaning.

Late Selection Theory

Shadow by ear

Shadow by
meaning

Decide what to
say

Testing the Theories


Dichotic listening task:


Shadow one message but listen for a
target word in both ears (tap when heard).


Late selection theory predicts no
difficulty hearing the target in either ear.


Attenuation theory predicts less
detection in non
-
shadowed ear.


87% detection in shadowed ear


8% detection in non
-
shadowed ear

Neural Evidence (Auditory)


An enhanced response occurs in the
primary auditory cortex but not earlier in
the auditory pathways.


Both EEG (using ERP) and PET show this.


The enhancement occurs quickly,
sooner than meaning can be interpreted.


Effects are signal attenuation and
enhancement, not complete filtering out.

Visual Attention


We can choose where to fixate our eyes
for greatest visual acuity.


Other portions of the visual field are
attenuated.


Visual attention need not be located
where the eyes are fixed.


Posner


subjects can attend to objects
up to 24 degrees from the fovea.


Shift of attention precedes eye movement.

Selective Attention

Spotlight Metaphor


Spotlight
can be broad or narrow
(degrees of visual angle).


Broad areas processed less well.


A narrow focal point gives optimal
processing but it takes time to move the
focus to other areas of the visual field.


We move our eyes around a complex
visual stimulus.


Neisser & Becklen’s shadowing task.

Neural Evidence (Visual)


Attention consists of enhanced neural
response in a particular spatial location
in the visual cortex.


By increasing neural activity in a particular
location, input to that location can be
processed faster.


Specific details are “higher order”
properties and take longer to recognize.


Enhancement comes from V4 not V1.

Neural Evidence

Monkeys showed greater
activity while waiting (b)
when the original stimulus
was on the saccade path.

Activity occurs on the
opposite side from the
stimulus.

Visual Search


Feature
-
based serial search


Neisser


Find the letter K in a string of letters.


Pop
-
out



locate a distinctive feature in
an array without searching each item.


Treisman & Gelade


locating a
conjunction of features takes longer than
locating a single, distinctive feature.


T among I’s & Y’s

400 ms


T among I’s & Z’s

800 ms

Visual Pop
-
Out

Can you find the owl?

From
Delphine Chedru


Spot
It! Find the Hidden Creatures
.

Can you find the bee?

Which is harder to see?


Why?

Treisman & Gelade’s Data

The Binding Problem


If different neurons process different
features of an object (color, motion,
lines) how are such features combined?


Feature integration theory

(Treisman)


people must focus attention in order to
synthesize features into a pattern.


Illusory conjunctions



mistakes in
binding when attention is disrupted.


See pink T, yellow S, blue N but report
seeing a pink S that was never presented.

Attention Enhances Features


Attentional enhancement can be based
on specific features not simply the
contents of a visual field.


Blue and green bars (macaques)


cell
firing is suppressed if green is attended.


Black and white teams and black gorilla:


8% of those attending the white team saw
the black gorilla


67% of those attending the black team saw
the black gorilla (both were black)


http://viscog.beckman.illinois.edu/flashmovie/23.php

Selective Cell Firing

Blue is attended

Green is attended

Cell fires despite presence of green

Cell firing is greatly reduced
despite presence of blue

Visual Neglect


Visual neglect may occur due to damage
to:


posterior parietal lobe


pulvinar (thalamus)


superior colliculus (eye
-
tracking)


People with injuries to the parietal lobe
have difficulty shifting attention from one
side of the visual field to the other.

Attention Deficit

Right parietal lobe
damage prevents
subjects from shifting
their attention to the other
visual field.

The first neglect
patient (a) has
copied the right
sides of both
figures, ignoring
the left.


The second patient
(b, c) neglects the
left sides when
copying but draws
a more complete
figure from
memory.

Halligan et al, 2003

Kinds of Deficits


Damage to the right parietal lobe
produces deficits in cued attention tasks:


No problem with items on the right but
inability to shift to items on the left.


Unilateral neglect



with severe damage
people totally ignore the left visual field.


Left parietal damage inhibits attention to
details.


Deficits occur across modalities

Object
-
Based Attention


Attention can be focused on particular
objects, not just regions of space.


Sometimes it is easier to attend to an
object (bumps on stimuli).


Inhibition of return



if we have already
looked at a location it is harder to return
to it.


Flickering squares take longer to identify
because already viewed, even when
rotated.

Two Attention Tasks

Two Theories

Spotlight theory



we move
our attention to parts of the
visual field.

Object
-
based theory



we move
our attention to objects.

Object
-
Based Neglect


Just as objects can be attended to
independent of their location, neglect
can apply to objects, not locations.


Some patients neglect one side of
objects regardless of which visual field
they occur in.

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.

Dual Task Processing

Automaticity


Practice reduces the need for attention
by reducing central cognition, making a
task automatic.


Practice enables parallel processing.


Spelke’s two tasks:


Read text for comprehension


Write down words read by an experimenter


After 6 weeks subjects could read at
normal speed and answer questions.

Stroop Effect


Color words were presented printed in
different ink colors.


Control stimuli were non
-
color words in
different inks or color bars (not words)


Subjects were asked to name the ink
color as quickly as possible.


Demo


Stroop Demo

Why it Happens


Automatic processes are difficult to stop.


It is nearly impossible to look at a word
without reading it.


Neutral words name non
-
colors so ink
can be named without interference.


Color words that conflict with ink color
take longer because reading the word
cannot be inhibited.

Practice With Stroop Tasks


What happens if you compare tasks that
are not well
-
practiced?


MacCleod & Dunbar asked subjects to
associate color names with shapes.

MacCleod & Dunbar’s
Conditions


Congruent


random shape was in the
same ink color as its name.


Control





white shapes were presented and subjects
said the name of the color for that shape


colored shapes were presented and
subjects named the ink color of the shape


Conflict



the random shape was in a
different ink color than its name.

Results


At first, color naming was more
automatic than shape naming and was
unaffected by congruence with shape.


After 20 days practice, shape naming
was affected by congruence with ink
color


Practice reversed the Stroop effect and
made shape naming like color naming.

Executive Control


Control of attention occurs in the parietal
lobes, but central cognition occurs in the
prefrontal cortex.


Damage to the prefrontal cortex impairs
executive control.


Response is stimulus
-
driven not intentional


Cannot do the Stroop task because
automatic processing takes over


Arbitrates between competing processes