The Stroop Task

1
The Stroop Task
2
Outline

• Overview of the Stroop Effect
• Other Stroop-like Interference Tasks
• Control conditions
• Semantic Effects
• Acoustic Manipulations
• Strategy
• Stimulus Onset Asynchrony
• Individual Differences
• Explanations
• Summary

3

• GREEN YELLOW
• BLUE BLUE
• YELLOW GREEN
• BLUE RED

4
The Stroop Task Can Teach Us About

• Attention
• Automaticity
• Learning
• Response Selection
• Word Reading
• Color cognition
• Experimental Methodology

5

• GGGGG A A OOO
• G A A O O
• GGGG AAAAA O O
• G A A O O
• GGGGG A A OOO

6
rabbit
7

• below above
• above

8

• LEFT

9
Variations

• Insufficient evidence to decide whether similar
  processes are involved in all of the Stroop-like
  variations.

10

• Dalrymple-Alford Budayr (1966) First to
  encourage presentation timing of stimuli
  individually. This method now dominates

Stroop effect
BLUE
BLUE
11
interference
facilitation
BLUE
BLUE
12
Control Condition

• rsmtlae fast
• rsmtlae fast
• rsmtlae fast
• rsmtlae fast

13
Control Condition

• fast red
• fast yellow
• fast red
• fast green

14
Control Condition

• fast red fast
• fast yellow ready
• fast red mouse
• fast green fruit

15
Control Condition

• fast red fast fat
• fast yellow ready double
• fast red mouse fat
• fast green plan fruit

16
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

17
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).

18
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

19
Strategy

• Composition of entire set of trials influences
  the participants strategy
• blocked vs. unblocked
• Cheesman Merikle (1984)
• Ps could use info regarding proportion of
  congruent primes if primes were perceived
  consly, but not if perceived unconsly (but
  uncons primes still affected responses)

20
Stimulus Onset Asynchrony (SOA)
complete stimulus (e.g. GREEN)
ignored stimulus (e.g. GREEN)
SOA
time
21
SOA

• Dyer (1971)
• Color naming - interference decreases with
  increasing SOA (0 500 ms SOAs used)
• Glaser Glaser (1982)
• Color naming - interference maximal at /- 100 ms
  SOA
• Word reading no effect of SOA

22
Hemispheric Differences

• Larger Stroop effect when the words are presented
  to the left hemisphere than the right

23
Age differences
Stroop Effect
0 6 20 60
Age
24
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 persons languages
• Whichever language someone was more proficient in
  caused more interference

25
Explanations

• Speed of Processing
• Automaticity
• Perceptual Encoding
• Parallel models
• Parrallel Distributed Processing

26
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.

27
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.

28
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

29
Parallel Models

• With fine tuning, Logans 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).

30
Summary

• 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)
• MacLeods review has been cited 365 times
  (1991-2004).
• Still not fully understood

31
1935 Stroops original article
1960s Research interest in Stroop paradigm
blossoms
1973 Dyers review of research on Stroop effect
1991 MacLeods review of research on Stroop
effect

• 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)