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Zhang, H., & Kornblum, S. (1998). The Effects of Stimulus-Response Mapping and Irrelevant Stimulus-Response and Stimulus-Stimulus Overlap in Four-choice Stroop tasks with Single-Carrier stimuli.

NOTE: This page is a short summary of the paper. The full text of the manuscript is not currently available online.

The standard Stroop task (Type 8) is normally run with congruent mapping instructions; i.e. given the Type 2 aspect of the task, subject are usually instructed to “respond to the color in the stimulus with its name”.  This necessarily locks the irrelevant SR (Type 3 constituent), and SS (Type 4 constituent) to the same value: either they are both consistent, or they are both inconsistent.  This confounding can be eliminated with a three (or more) – choice task, with congruent and incongruent mappings.

 

EXPERIMENT 1

The stimuli consisted of three words presented one above the other.  The middle word was the relevant stimulus.  The top and bottom words were the irrelevant stimulus and were always identical.  The responses were vocal.  Four ensembles were constructed: Types 2, 3, 4, and 8. Type 2 were used to examine the main effects of SR mapping, and SR and SS consistency in isolation.

 

RELEVANT &  IRRELEVANT, STIMULI & RESPONSES

There were four color words (RED, GREEN, BLUE, and YELLOW), and four digit words (TWO, FOUR, SIX, and EIGHT).

The responses were either color names or digit names (for details see Zhang & Kornblum, 1998).  Depending on the ensemble Type, the relevant and irrelevant stimuli were either both color words or digit words (Types 4 and 8), or the relevant stimuli were color words and the irrelevant stimuli digit words, or the other way round (Types 2 and 3)

Ensemble Type

RELEVANT S SET

RESPONSE SET

IRRELEVANT S SET

2

COLOR WORDS

COLOR NAMES

DIGIT WORDS

  DIGIT WORDS DIGIT NAMES COLOR WORDS

3

DIGIT WORDS COLOR NAMES COLOR WORDS
  COLOR WORDS DIGIT NAMES DIGIT WORDS

4

DIGIT WORDS COLOR NAMES DIGIT WORDS
  COLOR WORDS DIGIT NAMES COLOR WORDS

8

COLOR WORDS COLOR NAMES COLOR WORDS
  DIGIT WORDS DIGIT NAMES DIGIT WORDS

The responses were either color names or digit names.

 

SR MAPPINGS

For Type 2 and 8, the SR mapping was either congruent or incongruent.  For the congruent mapping the response was to say  the word presented (i.e. the relevant stimulus).  For incongruent mapping, the response was to say a word that was different from the relevant stimulus, but was in the same category (i.e. color or digit).

 

For Types 3 and 4, there were four different possible SR mappings: If the relevant stimulus was a color word, the response could be one of any of the four digit names; if the relevant stimulus was a digit word, the response could be any one of the four color names.  All four possible mappings were used, but each subject was run with only one mapping.

 

EXPERIMENTAL CONDITIONS

In Type 2, there were two mappings: congruent and incongruent. The irrelevant stimuli were neutral with respect to both the relevant stimuli and the responses.

In Type 3, there was a consistent and inconsistent SR condition; the relevant stimulus was neutral with respect to both the irrelevant stimulus, and the response.

In Type 4, there were also two consistency conditions: SS consistency, and SS inconsistency.  In both conditions the response was neutral with respect to both the relevant and the irrelevant stimuli.

The combinations for type 8 are shown in the table below:

 

 

 

 

 

 

S

R

S

 

 

 

 

A

BLUE

BLUE

BLUE

CONG.

 

B

BLUE

BLUE

GREEN

CONG.

C

BLUE

GREEN

BLUE

INCONG

D

BLUE

GREEN

GREEN

INCONG

E

BLUE

GREEN

RED

INCONG

Table 2

EXPERIMENT 2

The main purpose of Experiment 2 was to test the generality in nonverbal tasks of the results obtained in Experiment 1.  A second purpose was to include a neutral baseline for ensembles 2, 3, and 4 so that we could calculate facilitation and interference effects for these ensembles.

Instead of using color and digit words, like we had in Experiment 1, in experiment 2 we had actual color patches and digits.  Also, instead of presenting these one above the other, the color patches and digits were presented in small, side by side rectangles.  The middle rectangle had the relevant stimulus, the left and right rectangles had the irrelevant stimuli and were identical.

The relevant stimulus was either a color patch (red, green, blue, or yellow), or a digit (2, 4, 6, or 8).  The irrelevant stimuli were the same digits, plus 4 false fonts, and the same color patches plus a gray patch.  The responses were either color names or digit names.

 

EXPERIMENTAL CONDITIONS

With the exception of the type 1 ensemble, which had no overlap hence had all neutral trials, the experimental conditions in this experiment were identical to those in experiment 1, when making the following substitutions in table a: replace “ COLOR WORDS” with  “COLOR PATCHES”, and ”DIGIT WORDS” with “DIGIT”.

 

OVERALL RESULTS:

Type 2.

Congruent:           425ms.   444ms.

Incongruent:        672ms.   663ms.

 

Type 3.

SR consistent:     590ms.   536ms

SR inconsistent:  625ms.   573ms.

 

Type 4:

SS consistent:      594 ms.   571ms.

SS inconsistent:  625 ms.   597ms.

 

Type 8

Congruent –SR/SS consistent:         425 ms.   446ms.

Congruent – SR/SS inconsistent:     448 ms.   471ms.

Incongruent – SR incon/SS con:      656 ms.    662ms.

Incongruent –  SR con/SS incon:      679 ms.    684ms.

Incongruent – SR incon/SS incon:    713 ms.   696ms.

The error rate was low and did not differ between ensembles.

For all ensemble types and for both experiments, congruent was faster that incongruent, and consistent was faster than inconsistent.

RESULTS OF EXPERIMENTS 1 AND 2

 

Ensemble 8; condit.

Mapping

SR//SS

Response

RT (1)

RT 2

 

Stroop

Stroop

conditions

consistency

set

(exp. 1)

(exp. 2)

A

CONG.

SR+ //SS+

color

438

482

A – B

21

29

 

 

 

digit

412

410

A – B

26

21

B

CONG.

SR- //SS-

color

459

511

 

 

 

 

 

digit

438

431

 

 

C

INCONG.

SR – //SS +

color

691

722

 

 

 

 

 

digit

623

603

 

 

D

INCONG.

SR + //SS-

color

718

758

E – D

33

-6

 

   

digit

641

630

E – D

34

-3

E

INCONG.

SR- //SS –

color

751

764

 

   

digit

675

627

 

 

Ensemble

RT Exp. 1

RT Exp. 2

2

CONG.

color

438

492

2

CONG

digit

719

395

3

CONG

color

616

561

3

CONG

digit

565

512

4

CONG

color

625

570

4

CONG

digit

576

572

2

INCONG

color

719

728

2

INCONG

digit

626

599

3

INCONG

color

649

577

3

INCONG

digit

603

570

4

INCONG

color

653

609

4

INCONG

digit

597

585

Neutral…………………………………………563ms

 

COMMENTARY

1.  The Stroop effects in experiments 1 and 2 are almost identical, which generalizes our results to non word tasks.

2.  Condition C was faster than condition than condition E, and the two differ in the sign of SS only, which supports the notion that SS consistency has an effect (34ms).

3.  For experiment 1 we concluded that the Stroop effect is attributable to both SS and SR consistency, and that these consistency effects are not linearly additive.  These are fully supported by the results of Experiment 2.

 

RESULTS SUMMARY

By using single-carrier stimuli, and four-choice tasks with congruent and incongruent mappings, we were able to address several important issues in the study of the Stroop tasks:

1.  We eliminated the confounding between the stimulus and the response effects that inherent in the standard congruent Stroop task.

2.  We separated SS effects from the logical recoding hypothesis (cf. De Jong), which is impossible to do in two-choice, incongruent Stroop tasks.

3.  By using single carrier stimuli, we eliminated any effects attributable to differences in the basic processing speed of two different processing functions (reading, and color naming).

 

The results of both experiments converge on the same conclusion: the Stroop effect is the result of a combination of SS and SR consistency effects. This raises questions and concerns that were incorporated in an interactive activation model developed by Zhang, et al. (1999), which was also the precursor of the Computational DO Model.

 
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