interdimensional interference in the stroop effect: uncovering the...

Interdimensional interference in the Stroop effect: uncovering the cognitive and neural anatomy of attention

Friday, September 30, 2011

One property of an object (or display) can interfere with voluntary attention to another property.

Some examples......


red

5

55

5

+above


redgreenyellowredbluegreenbluered

yellowblueyellowgreen

bluegreenredblueyellowbluegreenred

yellowgreenyellowred

xxxmmmmmmhhhhhsssssshhhhxxxssssssxxx

mmmmmmssssss

mmmmmhhhh

greenblueyellowgreenredblueyellowredgreenredblueyellow


A B C D

The Stroop shows asymmetrical interference:

Words interfere with color naming but colors donot interfere with word naming.

Is this asymmetry due to the fact that words and colorsenter into a “horse race”?

RED


Theories of Color-Word Interference.

Word Color

The horse race idea

Response Output

Fast

Slow

BLUE

Blue YellowMonitor


A number of results indicates that (surprisingly) this cannotbe the correct answer.

Slowing the word reading route down does not prevent interference!


A number of results indicates that (surprisingly) this cannotbe the correct answer.GREEN

Slowing the word reading route down does not prevent interference!


It appears, instead, that word reading competes with colour naming because word reading is

more “automatic”.

We need to define more clearly what we mean by the term “automatic”. We will do this when we discuss a formal computational model of the

Stroop task.


We will discuss this model in detail later.


That the Stroop effect stems from differential relative automaticity is made clear in a study by MacLeod and Dunbar. People were trained to respond with a particularcolor name to each of four unique random polygon shapes. They were tested periodically with shapes presented in incongruent colors (e.g. the shape called ʻblueʼ printed in the color green). Early in training, shape naming showed interference from incompatible print colors, but color naming was unaffected by incompatible shapes. Midway through training, each dimension interfered equivalently with the other. Finally, after extensive training, incompatible shapes interfered with color naming but incompatible colors no longer interfered with shape naming. The complete reversal of the pattern of interference clearly resulted from the shift in relative automaticity of color names and shape names with practice. Practice also has profound effects on the standard color-word Stroop effect.


MacLeod and Dunbar

Yellow

Blue

Red

Green


“Yellow”

In early stages of training, the color (blue in this example) interfered with naming the object (‘yellow’) but the name associated

with the object (yellow in this case) did not interfere with naming the color.


In intermediate stages of training the interference was symmetrical.

The color of the object interfered with the color name associatedwith the shape.

The color name associated with the object interfered with naming the color that is carried by the object.

“Yellow”


In later stages of training, the interference was again asymmetrical.

The color name associated with the object (Yellow) interfered with naming the color (Blue) but there was no interference from the

color of the object (Blue) when the task was to produce the name associated with the object.

“The complete reversal of the pattern of interference clearly resulted from the shift in relative automaticity of colour names and shape names with practice.”

“Yellow”



Question 3 Is the following statement True or False? (a) True (b) False

Performance on baseline colours improves more after 20 days training than performance on baseline shapes.

a) True b) False

Cognitive control requires rapid choice amongstcompeting possibilities.

The hallmark of the Stroop is that the competitionis asymmetrical. One response is more prepotent than

another.

How does the brain control the response affordedby the word in favour of the color given a suitable

task instruction (i.e. name the color)?


Preliminary Neuroimaging

YELLOW

GREEN

RED

BLUE

********

*****

***

****

FAMILY

BOAT

CAT

FOOT

RED

BLUE

GREEN

YELLOW


Incongruent versus Control

Greater activation is seen in the anterior cingulate


Hypothesis: The ACC is involved in task-relevantcontrol of attention and/or response selection in the

presence of conflicting information.


An important empirical point

YELLOW

GREEN

RED

BLUE

********

*****

***

****

FAMILY

BOAT

CAT

FOOT

RED

BLUE

GREEN

YELLOW

AB

A shows greater activation of ACC than B!


There is no response conflict in a color word combinationlike YELLOW so why is there more ACC activation relative

to SECRET where there is response conflict?

Maybe the conflict for YELLOW lies in the fact that the observer has to work harder to decide which dimension to attend to in order to produce a correct response? After all, both dimensions now belong to the response set (both the name of the color and the word match) so each dimension

may compete for attention more strongly than the color word dimensions in the control condition.


“The most plausible explanation for these Stroop findings is that the anterior cingulate discriminates between sources of

information, directing attention to the appropriate source, regardless of conflicting information or response tendencies. In essence, the function of the anterior cingulate in the Stroop task may be to maintain the goal of attending to and responding to

color.”

The anterior cingulate maintains task set even in the absence ofconflict.


MacLeod and MacDonald:

Maintenance of task set is not as strong (has a more lax criterion) when the word has the same response as the color.

But there is a problem... Carter et al use event related fMRI.

80% incongruent and 20% congruent ! Low conflict and high strategic maintenance of task set.

20% incongruent and 80% congruent! high conflict and lowstrategic maintenance of task set.

BLUE FOOTYELLOW> >Task set:


80% Incongruent Blue Green Yellow Red Blue Red Green Blue

20% Incongruent Red Blue Green Yellow Green Blue Red Green

What is the state of the brainon this trial?


MacLeod and MacDonald:

Maintenance of task set is not as strong (has a more lax criterion) when the word has the same response as the color.

But there is a problem... Carter et al use event related fMRI.



BLUE FOOTYELLOW> >Task set:



Why is this condition low conflict?

Answer: The subject is given lots of practice with incongruentpairs (80%!) and so learns to cope with the conflict by

strong maintenance of task set.


The subject encounters incongruent pairs rarely (20%) andmostly experiences congruent pairs. Task set need not

be strongly maintained (the word is often the same as the color)but conflict when it does occur is high.


When does ACC activation occur more strongly for Incongruentpairs relative to Congruent pairs, when Incongruent pairs

occur 80% of the time or 20% of the time?

Answer: The ACC is more active when Incongruent pairs occur 20% of the time!

The ACC responds to high conflict !

If the ACC is sensitive to the maintenance of task set then ACCshould be more active in the 80% incongruent condition (high

task set maintenance) than the 20% incongruent condition (low task set maintenance.

If the ACC is sensitive to the resolution of conflict then ACCshould be more active in the 20% incongruent condition (highconflict) than the 20% incongruent condition (low conflict).


So we have a little mystery on our hands...

Th ACC is active relative to a baseline condition even when there is no conflict between the word and the color (ie. when the color and

the word match).

This result implies that the role of the ACC is to maintain the right task set (name the color) when the word invites the same response.

Control involves maintaining the color task set and not switching to the word reading task set (both task sets give the same response

when the word matches the color).

The rival claim is that the ACC is required when there is highconflict between the color naming and the word reading task set.

The evidence in support of this claim is that the ACC is more active in conditions of high as opposed to low task conflict.


20% Incongruent

Red Blue Green Yellow Green Blue Red Green

What is the state of the brainon this trial?

How does this idea work:(i) Notice that the 20% Incongruent condition is a Low Task Set/High Conflict situation because there is a low probability of encountering an Incongruent Trial. (ii) So the brain calibrates itself to expect (in general) Congruent Trials.(iii) But when an Incongruent Trial is unexpectedly encountered, there is sudden (unexpected) high conflict.(iv) To overcome the conflict, the brain immediately “ramps up” the strategic control of task set. (v) So the increased activation of the ACC in high conflict situations is actually due, according to this idea, not to any mechanism that directly controls or suppresses the automatic response to the word, but to a sudden increase in the control of the colour naming task set!


interdimensional interference in the stroop effect: uncovering the...

Documents