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Taxonomy of DO Ensembles

The dimensional overlap model provides a useful way of talking about compatibility tasks (more info: Why study compatibility effects?). 

When all the individual stimuli used in a task vary on a common stimulus dimension (e.g. red and blue varying on the color dimension), and all the individual responses that are used in that task also vary on a common response dimension (e.g. left and right varying on spatial dimension), they form a stimulus set and a response set, respectively. When these two sets are put together in a larger set, that larger set is called an ensemble.

In addition to a relevant stimulus dimension and a response dimension, a task may also have one or more dimensions: irrelevant stimulus dimensions that subjects are instructed to ignore .

Different task may be characterized by the properties of the ensemble that they use.  If the individual sets in the task are similar, be they a stimulus set and response set, or two stimulus sets, then we speak of that ensemble as having dimensional overlap. (more info: What is Dimensional Overlap?)

This allows us to define a broad framework for classifying different types of ensembles, or tasks,  based on the dimensional overlap, or set-level similarity, of the ensembles in the task. Dimensional Overlap (i.e similarity) is of course a continuous property; however, we can talk about tasks that either do, or not  have overlap between their different components.  A framework with three possible dimensions (relevant stimulus, irrelevant stimulus, response), all of which can either overlap or not overlap, produces a taxonomy of eight possible dimensional overlap ensembles or tasks types.

These eight types constitute the dimensional overlap ensemble taxonomy.

Type Relevant S-R
Overlap?
Irelevant S-R
Overlap?
S-S
Overlap?
Example Tasks
1 no no no CRT task
2 yes no no Fitts task
3 no yes no Simon task
4 no no yes Flanker Task
Stroop-like Tasks
Cross-modal tasks
5 yes yes no Hedge and Marsh task
6 yes no yes (not possible?)
7 no yes yes SS x SR task
8 yes yes yes Stroop task

The first ensemble in the taxonomy is a Type 1 task, which is a standard Choice Reaction Time (CRT) task with no dimensional overlap. This is technically not a compatibility task at all: it contains no dimensional overlap between any of its components. However, it is often used as a “neutral” condition in compatibility experiments in order to establish a comparison point for measuring the benefit of consistency versus the cost of inconsistency (more info: Choice Reaction Time (CRT) tasks).

After the Type 1 task, the taxonomy enumerates all of the possible combinations of dimensional overlap among the three dimensions, all the way up to the Type 8 task, which has overlap among all the dimensions: relevant stimulus, irrelevant stimulus, and response. The well-known Stroop task is an example of a Type 8 task (more info: The Stroop Task).

Click on the links in the above table for a more detailed description of the experiments and results of tasks belonging to each ensemble.

As an easy reference, the table below shows some sample stimulus and response sets that could be used to produce tasks of each type in the taxonomy.

Type Relevant Stimulus
Dimension
Irrelevant Stimulus
Dimension
Response
Dimension
Instructions
1 color vertical
position
left/right
key-press
press the left key for a green stimulus
press the right key for a blue stimulus
2 color digit color  names say “green” for a green stimulus
say “blue” for a blue stimulus
or
say “blue” for a green stimulus
say “green” for a blue stimulus
3 color horizontal
position
left/right
key-press
press the left key for a green stimulus
press the right key for a blue stimulus
4 color color word digit names say “two” for a green stimulus
say “four” for a blue stimulus
5 color horizontal
position
colored left/right
key-press
press the blue key for a blue stimulus
press a green key for a green stimulus
or
press the green key for a blue stimulus
press a blue key for a green stimulus
6 (not possible?)
7 color horizontal position
and color word
left/right
key-press
press a left key for a green stimulus
press a right key for a blue stimulus
8 color color word color names say “blue” for a blue stimulus
say “green” for a green stimulus
or
say “green” for a blue stimulus
say “blue” for a green stimulus

 


 

NOTE: Although the above taxonomy represents the official taxonomy of the ensembles explored by the dimensional overlap model, it is possible to explore extensions of this taxonomy by examining new task dimensions.

For example, Stevens and Kornblum (2000, July) presented an extension of the taxonomy that distinguishes between the response dimension and the goal dimension in a task. The goal dimension is defined as the intended outcome of a response action, which may be different from the response action itself.

Hommel (1993a) performed a variation of the Simon task in which subjects were told to light up a light by pressing a key when a stimulus appeared. In these tasks, subjects either needed to press a right key to light up a light on the right side, or press a left key to light up a key on the right side. Hommel (1993a) showed that this consistency between the response (key position) and goal (light position) had a measurable effect on reaction time. Stevens and Kornblum (2000, July) were able to extend the computational dimensional overlap model to include overlap with a “goal dimension” to account for this effect (more info: The Computational Model).

 

 
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The Flanker Task

The Flanker Task, also sometimes called a Eriksen Task, is a choice reaction time task where there is dimensional overlap between the irrelevant stimulus and the relevant stimulus. In the dimensional overlap taxonomy, it is considered a Type 4 task. Other Type 4 tasks include the Stroop-like task and Cross-Modal tasks.

Charles Eriksen (Eriksen & Eriksen, 1974; see also Eriksen, 1995; Eriksen & Schultz, 1979; Cohen & Shoup, 1993, 1997; Miller, 1982, 1991) studied the effects of distracting “flanker” stimuli that appear around or near a relevant target stimulus. In a typical Eriksen task, subjects are shown a string of letters on a screen, and are told to press a left key or a right key depending on what letter appears in the center of the screen (the target letter). The surrounding flanker letters are irrelevant, but can be either consistent (“HHH”) or inconsistent (“SHS”) with the target. Responses are faster and more accurate for consistent stimuli than for inconsistent stimuli. The difference in reaction time is called the Eriksen effect or the flanker effect.

Flanker Task

Targets and flankers are both defined as values along the same dimension: in the example above, it is letter. As a result, the relevant and irrelevant stimulus have perceptual and conceptual overlap. Moreover, because the overlap is between stimulus properties, consistency is a property of the stimuli themselves, and is independent of the mapping instructions. However, because different letters are usually assigned to different responses, a confound arises in most tasks: when the stimulus is S-S consistent, the response assigned to the flankers is different from the response assigned to the target. This confound is central to the debate about different explanations of the S-S consistency effect.

Eriksen tasks permit a large number of variations, while still producing the same effect. For example, although flankers and targets are generally letters, they can also be words or shapes or symbols (e.g. Hommel, 1995; Shaffer & LaBerge, 1979; Zhang & Kornblum, 1998). Also,  although flankers are usually presented to the left and right of the target, they can also be presented above or below the target, or in other patterns around it (e.g. Eriksen & Hoffman, 1973; Eriksen & St. James, 1986; Eriksen & Murphy, 1987; Yantis & Johnston, 1990; Zhang & Kornblum, 1998).

The key factor that all flanker tasks have in common is the perceptual dimensional overlap between the irrelevant stimulus and the relevant stimulus.


NOTE: There are some times when you will see people use the term “Flanker task” to refer to tasks where left and right arrows are assigned to left and right key-presses, and each target arrow is flanked by irrelevant flanker arrows that are either consistent or inconsistent with the target arrow. In the Dimensional Overlap taxonomy, this is not a Type 4 task: it is a Type 8 task, like the Stroop task. Even though this task has flankers, the dimensional overlap model contends that cognitive processing in this task is fundamentally different from processing in the standard Eriksen task, because it adds overlap between the stimulus dimensions and the response dimension.

 
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Kornblum, S., & Stevens, G., (2002). Sequential Effects of Dimensional Overlap: Findings and Issues.

This is the Association Lecture delivered at the Nineteenth International Symposium on Attention and Performance, held in Kloster Irsee, Germany, July 16-22, 2000.

In this lecture Kornblum melds the two areas of research in which he has spent most his research time, the dimensional overlap model and his earlier work in sequential reaction time effects, and finds that they complement each other well, and also raises new and interesting questions.

 
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Stevens, G. T. (2000). The locus of consistency effects in Simon, Eriksen, and Stroop tasks: New data and a comparison of models.

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

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Kornblum, S., Stevens, G. T., Whipple, A., & Requin, J. (1999). The effects of irrelevant stimuli: The time course of S-S and S-R consistency effects with Stroop-like stimuli, Simon-like tasks, and their factorial combinations.

[intro]

The first section of this paper describes in detail the computational model and its processing assumptions.

We conducted two new experiments for the explicit purpose of testing the predictions made by the computational model.  In both experiment we investigated the time course of S-R and S-S consistency.  In both experiments there was one condition in which there was no DO – that was the neutral condition (Type 1).  In experiment 1, the irrelevant stimulus overlapped with either the relevant stimulus (Type 4) or with the response (type 3), but not with both.   The delays occurred in a relatively narrow time range: (SOA = 0 – 200 ms).  In the second experiment the relevant stimulus overlapped with the irrelevant stimulus, as well as with the response (Type 7).  The range of delays was extended: (SOA = 0 – 800 ms).

EXPERIMENTS 1 & 2

 

Stimuli and Responses

The responses are left or right key presses.

The stimuli consisted of a rectangle (1.5 cm. x 3.3cm.) in which three attributes could be presented: color, position, and word.   Color was the relevant attribute; position and word were both irrelevant.  The color was either blue or green.  “Position” refers to the particular part of the rectangle in which the color was presented: upper/lower half – left/right half.  “Word” refers to a word which was presented in the middle of the rectangle.  The word was either “blue”, “green”, “detail”, or “novel”.

 

Fig.1 from SK, GTS, AW, JR, (1999) (P. 689)

 


General Method

Each trial began with the presentation of the four corners of the rectangle.  This also served as the beginning of the warning interval which was of random duration.  At the end of the warning period, the rectangle was completed by lines joining the four corners.  In one condition, the zero delay condition, color (the relevant stimulus), word, and position (the irrelevant stimuli) were all presented in the rectangle simultaneously.  In the non-zero delay condition, only the irrelevant stimuli were presented (position was indicated with gray). Following a short delay of between 50 and 800 ms. the gray in the rectangle was replaced by either the color blue, or the color green.  The rectangle display was terminated by the subjects’ response.

Experiment 1

The stimuli: Type 1, 3, and 4.

Delays: 0, 50, 100, and 200.

Each stimulus Type was run in a separate block at one delay.  The individual stimuli within each type were randomized within that block.

(see Fig.  x )

 

Results

1. There was no effect of delay in either the neutral or the Type 3 conditions, whether consistent or inconsistent.

2. The largest effect of delay was for the Type 4, (S-S overlap), inconsistent condition:  as delay increased, RT increased steeply.  However, for the consistent condition there was no effect of delay.

3.  The effect of delay on consistency effects differed greatly between Type 3 (S-R) and Type 4 (S-S) conditions.  As delay increased, the Type 3 SR consistency effect decreased, whereas the SS consistency effects  increased.  These data are in accord with those reported in a similar experiment ( Kornblum, 1994).

4.  The RT for Type 3 (S-R overlap) was faster for consistent than for inconsistent trials.

 

here I suggest including the table on p. 691, as well as inserting a simple graph for these mean data.  It would just make the results so much easier to see.

 

 Experiment 2.

The stimuli:  Types 1, and 7.

Delays: 0, 100, 200, 400, 800.

Each stimulus Type was run in a separate block, at one delay.  Within each block, one third of the trials were neutral wrt both the relevant stimuli and the responses, the other two third overlapped with both the stimuli and the responses: one sixth were doubly consistent (c/c), one sixth were doubly inconsistent (i/i), one sixth were S-S consistent and S-R inconsistent (c/i), and the remaining sixth were S-S inconsistent and S-R consistent (i/c).

Note: the value of S-S consistency is specified before the value of S-R consistency (e.g. c/i for S-S consistency, etc.)

 

Results

1.  RT’s for doubly consistent (c/c) and doubly inconsistent (i/i) conditions were the fastest and slowest respectively at all delays.

For the mixed consistency conditions at zero delay:

2.  The RT for c/i, was indistinguishable from the RT at doubly inconsistent (i/i) condition.

3. Similarly, the RT for i/c was indistinguishable from doubly consistent (c/c) condition.

 

?  Table 3, on p. 694; SK, GTS, AW, JR, (1999).

 

SIMULATIONS

Because in Experiment 2, the effects of both S-S and S-R overlap were examined in a broad range of SOA values, the results of Exp. 2 were simulated first. The parameters of the model were therefore set to provide the closest fit to the empirical data of Exp. 2.  In order to demonstrate the robustness of the model the parameters used for the simulation of Exp. 2, were then changed, in a theoretically appropriate way, to simulate the data of Exp. 1.

In addition, the data of two comparable experiments in the literature were simulated as well.

 

EXPERIMENT 2

The correlation between the empirical and simulated mean RT difference (i.e. RT – neutral) for the four experimental conditions was .9283.


EXPERIMENT 1

For Type 3, the correlation between the empirical and the simulated data was .9877, for Type4 it was .9460

For the two studies in the literature:

1.  Hommel (1997), Experiment 2.

For the two conditions of the experiment, the correlation between the empirical and the simulated data was .9968 for condition 1 (the horizontal condition), and .9999 for condition 2 (the vertical condition).

 

2.  De Jong et al. (1994), Experiment 3.

The correlation between the empirical data and the simulation was .9565

 
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Zhang H., Zhang, J., & Kornblum, S. (1999). A Parallel Distributed Parallel Processing Model of Stimulus-Stimulus and Stimulus-Response Compatibility

This is a precursor of the PDP model which, after some modifications, became the Computational DO Model.

This start of the model is the dimensional overlap taxonomy.  The events generating Reaction Times are assumed to take place in a network consisting of multiple parallel processing layers (Input – Intermediate – and Output).  Earlier layers may send continuous, partial activation to later layers, continuously.   Thus, unlike the original DO model and its later computational form, this PDP version of the DO model is not a discrete stage model.  While it permits information transmission within the same layer, it does not permit feedback from a later to an earlier layer.

ARCHITECTURE

A stimulus or response dimension (e.g. color) is represented by a module which is made up of neuron-like nodes.  Nodes represent a stimulus or response feature.  The number of nodes within a module is determined by the number of such features (e.g. particular colors, such as red, or blue…).  Feature nodes within the same module are negatively connected, mutually inhibitory, and so weighted as parameters.

Modules are arranged in three layers.  The input layer represents physical, carrier-specific stimuli; e.g. colored ink, or color words.  The intermediate layer represents abstract concepts; e.g. color, location.  The output layer represents responses; e.g. color names, key presses.

Modules and nodes in the input layer receive their input from the external environment via “task” lines.  “Task lines” represent the attention allocated to different stimulus dimensions, and is thus one of the parameters in the model.  The nodes in the input layer generate and send activation to the corresponding nodes in the intermediate layer via “carrier lines”.  “Carrier lines” represent the strength between carrier-specific stimuli and their concepts, and is another parameter in the model.  The nodes in the intermediate layer produce and send activation to corresponding nodes in the output layer via “control” lines. “Control lines’ represent the SR mapping, i.e. the controlled processes postulated in the DO model.  All connections are between modules in different layers.

SS OVERLAP

Because stimuli and responses may be multidimensional, multiple modules may exist in each layer.  For SS overlap, (e.g. Ensembles 4 and 8,) the input layer may have two modules: one for the relevant stimulus, the other for the irrelevant stimulus.  The model assumes that these two modules converge on a common module in the intermediate level.

SR OVERLAP

For SR overlap (e.g. Ensemble 2) the corresponding nodes in the intermediate and output layers are linked via “automatic line”, (which is an implementation of “automatic activation” in the original DO model).

CONGRUENT/INCONGRUENT MAPPING

The connection patterns for congruent and incongruent mappings are quite similar: corresponding nodes in the intermediate and output layers are connected via automatic lines; however, for incongruent mappings, instead of connecting the control line to the same nodes, it connects to different nodes, thus producing response competition – just as in the original DO model.

IRRELEVANT STIMULI

In Ensemble 3 the stimulus is two-dimensional.  Both the input layer and the intermediate layers each have two modules (relevant and irrelevant).  Since the irrelevant dimension overlaps with the response, the nodes in the irrelevant dimension are connected to the corresponding nodes in the output layer via automatic lines.  The nodes in the relevant dimension are connected via control lines thus, once again, generating response competition.

With these “architectural principles” now in place, a PDP network for ensembles 1 to 8 may be constructed.  Such networks will necessarily differ from each other architecturally when they differ in overlap, or in mapping.

PROCESSING

The presentation of a stimulus feature is assumed to activate the corresponding node in the input layer with a value of 1, which is then clamped down, otherwise it remains at 0.  These values are fed  continuously to the appropriate feature nodes in the output layer.  Once the activation of any node in the output layer reaches the response threshold, an overt response is executed.

With some additional processing assumptions (see Zhang, et. al, 1999), and the setting of a number of parameters (including: threshold; the weight for carrier line, control line, and automatic line; mutual inhibition) successful simulations were run with this model on the data of several of our experiments.

The Computational Dimensional Overlap Model incorporates many of the features of this model, but also changes some features of this model to bring the computational model more in line with the original process model. For example, this model is a continuous processing model that does not process stimulus and response information in discrete stages, like the original process model describes. The final implementation of the computational model keeps the network-activation principles of this model while also implementing the property of stage-like processing.

 
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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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Stevens, Greg., & Kornblum, S. (1998). The Flanker Consistency Effect: S-S or S-R?

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Kornblum, S., & Stevens, G. T. (1997, November). Reverse consistency effects and logical recoding: Insights from four-choice tasks.

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

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Stevens, G. T., Whipple, A., Requin, J., & Kornblum, S. (1996). The time-course of S-S and S-R consistency effects: Data and model.

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

However, the data and model presented at this conference were also published in Kornblum et al. (1999).

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