the stroop task

Perceptron Example:

Computational model for the Stroop Task

Jaeseung Jeong, Ph.D

Department of Bio and Brain Engineering,

KAIST

GREEN YELLOW

BLUE BLUE

YELLOW GREEN

BLUE RED

The Stroop Task Can

Teach Us About:

• Attention

• Automaticity

• Learning

• Response Selection

• Word Reading

• Color cognition

• Experimental Methodology

GGGGG A A OOO

G A A O O

GGGG AAAAA O O

G A A O O

GGGGG A A OOO

rabbit

below above

* * *

above

“LEFT”

Variations

• Insufficient evidence to decide whether

similar processes are involved in all of the

Stroop-like variations.

• Dalrymple-Alford & Budayr (1966): First to

encourage presentation & timing of stimuli

individually. This method now dominates

300

400

500

600

Congruent Incongruent

Tim

e (

ms)

BLUE BLUE

Stroop

effect

300

400

500

600

Congruent Incongruent Control

tim

e (

ms

)

BLUE BLUE

interference

facilitation

Control Condition

####### rsmtlae fast




Control Condition

fast red

fast yellow

fast red

fast green

Control Condition

fast red fast

fast yellow ready

fast red mouse

fast green fruit

Control Condition

fast red fast fat

fast yellow ready double

fast red mouse fat

fast green plan fruit

Semantic Effects

• Semantically-related distractor words (e.g.

blood, sky) have been used instead of

neutral words (e.g. double, fruit):

– some interference; more so as the semantic

association between word & color increases

– facilitation: small & dependent upon the

control condition used

• Using color words not in the response set

(e.g. purple) reduces the Stroop effect

Semantic Effects (cont) rabbit

• Congruent words facilitate responses

(compared to unrelated word or nonword)

• Same category words interfere most

• Associative word (e.g. “cheese” on picture

of a mouse) is same as an unrelated word.

• Interference in naming the color of an

incongruously colored object (e.g. a blue

banana), compared to a neutral object (e.g.

a blue book).

Acoustic Manipulations

• Using a manual response rather than vocal reduces interference

• Tying up the articulatory system (e.g. by saying “blah, blah …”) and using a manual response to the color reduced interference

• Interference increases with increasing pronouncability of nonwords, and with increasing similarity between nonwords and incongruent color words

Strategy

• Composition of entire set of trials

influences the participants’ strategy

– blocked vs. unblocked

• Cheesman & Merikle (1984):

– P’s could use info regarding proportion of

congruent primes if primes were perceived

cons’ly, but not if perceived uncons’ly (but

uncons’ primes still affected responses)

Stimulus Onset Asynchrony (SOA)

time

complete

stimulus

(e.g. GREEN)

ignored

stimulus (e.g.

GREEN)

SOA

SOA

• Dyer (1971):

– Color naming - interference decreases with

increasing SOA (0 – 500 ms SOA’s used)

• Glaser & Glaser (1982):

– Color naming - interference maximal at +/-

100 ms SOA

– Word reading – no effect of SOA

Hemispheric Differences

• Larger Stroop effect when the words are

presented to the left hemisphere than the

right

Age differences

Age

Str

oop E

ffect

0 6 20 60

Language - Bilinguals

• Stimulus: vert or green

• Response: “red” or “rouge”?

• Between-language interference ~ 75% of within-language interference

• Magiste (1984, 1985) studied relative proficiency of the person’s languages

– Whichever language someone was more proficient in caused more interference

Explanations

• Speed of Processing

• Automaticity

• Perceptual Encoding

• Parallel models

• Parrallel Distributed Processing

Speed of Processing

• Words read faster than colors are named

• Response from word reaches response

stage before response from color

• Results in interference / facilitation

• However, if SOA causes color to reach

response stage before word, does NOT

lead to reversal of Stroop effect.

• Therefore, theory is inadequate.

Automaticity

• Word reading is automatic & obligatory, color naming is a more controlled process.

• Automatic processes can interfere with controlled processes, but not vice versa

• Strategies should not affect automatic processes

• However, strategies caused by the % of congruent / incongruent trials do affect results

• Automaticity may be continuous rather than dichotomous: – This allows attention to assert some influence, but the

theory then looses some specificity and ability to test predictions decreases.

Parallel Models

• Response stage is active from start of trial.

• Each response option gains support as trial

goes on.

• Once a response reaches a threshold, that

response is chosen.

• Problems:

– Predicts symmetrical facilitation & interference. But a

solution is possible

– Could have same problems as speed of processing

account, but these are also fixable

Parallel Models

• “With fine tuning, Logan’s model can

encompass the existing data. However,

parallel models expressed only at the

conceptual level tend to have more ‘free

parameters’ than do sequential models,

which may be part of why they appear to

be more successful.” (MacLeod, 1991,p. 192).

Negative Priming

Table 1. Comparison of RTs for each NP condition for human behavioral data

Mean RTs ± SD (msec)

NP NP1 830 ± 274.9

NP2 708 ± 210.1

NP3 730 ± 234.1

non-NP Incongruent (NP1) 787 ± 288.6

Neutral (NP2) 702 ± 213.6

Congruent (NP3) 659 ± 202.4

Chung et al., Journal of Computational Neuroscience (In press)

Table 3. Comparison of RTs for each NP condition between conventional PDP and

TDNN models

Conventional PDP TDNN

(mean RTs ± SD) (mean RTs± SD)

NP NP1 16.3 ± 6.0 123.8 ± 138.2

NP2 13.4 ± 4.3 107.1 ± 31.5

NP3 12.2 ± 3.7 103.9 ± 34.3

non-NP Incongruent (NP1) 16.2 ± 6.1 113.2 ± 60.3

Neutral (NP2) 13.5 ± 4.3 104.8 ± 39.1

Congruent (NP3) 12.2 ± 3.7 100.0 ± 32.2

Chung et al., Journal of Computational Neuroscience (In press)

• Jensen (1965): w/ multiple administrations, the Stroop test is probably more reliable than any other psychometric test.

• Modifications only affect the magnitude (its quantitative form), not the pattern of the effect (its qualitative form

• 1935 – 1989: 700+ articles (~300 applied & ~400 theoretical)

• MacLeod’s review has been cited 365 times (1991-2004).

• Still not fully understood

Summary

2004: Time for another review? “I look forward to the progress that will be examined in the

subsequent review of the Stroop literature some time early in the next millennium” (MacLeod, 1991, p. 193)

1935: Stroop’s original article

1960’s: Research interest in Stroop paradigm blossoms

1973: Dyer’s review of research on Stroop effect

1991: MacLeod’s review of research on Stroop effect

the stroop task

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