Difference between revisions of "CNP SCWT"

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=== Data Distributions ===
 
=== Data Distributions ===
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[[File:SCWT_Mean_RT_Inc.JPG]]
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[[File:SCWT_Mean_RT_Inc-Con.JPG]]
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=== References ===
 
=== References ===

Revision as of 12:43, 27 June 2011

go back to HTAC


Basic Task Description

The Stroop task is a classic psychological test of inhibitory control. In the task, color words (typically red, green, and blue) are printed in an ink color that does not match what the words say (e.g., the word green is printed in red ink). Because the reading response is an automatic and habitual tendency in literate individuals, the participant must inhibit this reading response in order to identify the color of ink the word is printed in. In most Stroop task paradigms, there are at least two conditions—congruent and incongruent. In the congruent condition, the color words are printed in an ink color that matches the word. In the incongruent condition, the color word and the ink color do not match. Then, depending on the particular Stroop method, the time with which an individual can identify the ink color in the congruent and incongruent conditions is compared to give an index of inhibitory control. The current Stroop task uses a computer paradigm, in which the colors are represented with three response keys. Throughout this task, it is the goal of the participant to hit the key that corresponds with the ink color, not what the words say. There are also practice trials that help acclimate the participant to the task.

Task Procedure

This version of the Stroop was programmed in E-Prime 2.0. Participant responses are made on computer keyboard, using the right, down, and left arrow keys. At the beginning of the task, instructions are presented on the screen in yellow, size 16 Arial font, with a black screen background. The instructions are as follows:

Slide 1:

"In this task, you will see a word on the screen.

Please respond as quickly as possible to

the INK COLOR each word is printed in."

Slide 2:

"If the word is in red ink please respond quickly with the LEFT key.

If the word is in green ink please respond quickly with the MIDDLE key. If the word is in blue ink please respond quickly with the RIGHT key.

The ink colors are above your response keys if you forget.

Please ask the experimenter to start the PRACTICE when you are ready."

Each practice trial begins with a target word presented on a black screen (150 ms), followed by a blank screen for 1850, 1900, or 1950 ms. A fixation point (white +) is then presented for 250 ms. The time limit for responding to the target stimulus is 2000 ms (beginning at stimulus onset). The initial block of 18 practice trials includes congruent words only, in which the word and ink color are the same.

Following these initial congruent practice trials, participants are then shown another instruction slide that prepares them for the mixed block of congruent and incongruent practice trials:

"In the previous trial, the word always matched the ink color.

In the next trials, sometimes the word and the ink color will not match. For example, the word blue may be printed in red ink, like this:" (example given)

When this happens, you should still respond to the color of the ink, NOT what the word says. So for the word above, you would hit the (red) key"

Another instruction slide then appears:

"Remember: respond as quickly as possible to the color of the ink, NOT what the word says.

If the word is in red ink please respond quickly with the LEFT key. If the word is in green ink please respond quickly with the MIDDLE key. If the word is in blue ink please respond quickly with the RIGHT key.

Please ask the experimenter to start the PRACTICE when you are ready."

A second block of practice trials are administered in which there is a mix of congruent (75%) and incongruent (25%) trials. A total of 24 mixed practice trials are presented.

Another instruction slide then appears:

"We will now start the final task. Do the same as you did

previously: Respond as quickly as possible to the color of the ink, NOT what the word says.

If the word is in red ink please respond quickly with the LEFT key. If the word is in green ink please respond quickly with the MIDDLE key. If the word is in blue ink please respond quickly with the RIGHT key.

Please ask the experimenter to start the TEST when you are ready."

Experimental trials follow the same general parameters as the practice trials. A total of 152 experimental trials are administered - 98 congruent and 54 incongruent. For congruent trials, word color is randomly selected. For incongruent trials, word color is randomly selected with replacement. Following each stimulus, three blank screen delays (1850, 1900, 1950 ms) are presented in a semi-randomized manner that is consistent across subjects. Subjects have 2000 ms from target stimulus onset to make their response. Blank screen delay intervals are presented with the following frequencies:

  • Congruent Trial Delays:
    • 1850 ms: 39 trials
    • 1900 ms: 27 trials
    • 1950 ms: 32 trials
  • Incongruent Trial Delays:
    • 1850 ms: 14 trials
    • 1900 ms: 22 trials
    • 1950 ms: 18 trials

Task Structure Detail

This is what we had worked on before, but could use updating. We'd like to capture a schema that can handle each of the tasks in the CNP, so please think general when editing -fws

  • Task Structure (please given an overview of the task procedures here [i.e., overall design, block, trial, and within-trial event structure and timing])
    • The SCWT has two instructional screens at the outset, followed by practice trials and the experimental session.
      • Two instructional screens. Screens are advanced with a mouse click from the examiner.
        • 1. Basic task description.
        • 2. Explanation of response key mapping.
      • Practice trials, congruent block (total of 18 trials).
        • Target Stimulus Slide (150 ms).
        • Blank screen delay (1850-1950 ms).
        • Fixation slide (250 ms).
      • Instruction screen introduces the incongruent practice trials.
      • Practice trials, incongruent/congruent mixed block (total of 24 trials).
        • Target Stimulus Slide (150 ms).
        • Blank screen delay (1850-1950 ms).
        • Fixation slide (250 ms).
      • Instruction screen introduces the experimental trials.
      • Experimental trials (152 trials).
        • Target Stimulus Slide (150 ms).
        • Blank screen delay (1850-1950 ms).
        • Fixation slide (250 ms).
      • End. Thank you screen presented.
    • Timing
      • Instruction screens are static until advanced by examiner with a mouse click.
      • Target Stimulus Slide (150 ms).
        • Time limit for stimulus response is 2000 ms.
      • Blank screen delay (1850-1950 ms).
      • Fixation slide (250 ms).
      • The ending thank you screen is static until advanced by the examiner with left mouse click.
  • Stimulus Characteristics
    • sensory modality: Visual. Fixation and arrows are white and appear on a black blackground. Instructions are yellow text in size 16 Arial font presented on a black background. Target stimulus words are red, green, or blue in size 24 Arial font presented on a black background.
    • functional modality: visuoperceptual and linguistic (understanding of text).
    • presentation modality: computer display, directions are assisted by examiner.
  • Response Characteristics
    • responses required: Left, bottom, or right arrow key press.
      • effector modality: Manual button press.
      • functional modality: Manual button press.
    • response options (e.g., yes/no, go/no-go, forced choice, multiple choice [specify n of options], free response): Forced choice.
    • response collection (e.g., examiner notes, keyboard, keypad, mouse, voice key, button press): Button press and recording of responses in Eprime 2.0.

Task Schematic

SCWT Schematic 2.JPG

Task Parameters Table

File:.png

Stimuli

Stimuli consist of a central white fixation cross and colored words presented against a black background. Three different words (red, green, blue) were printed in either red, green, or blue ink. Congruent trials consist of a word printed in the same color ink. Incongruent trials consist of a word printed in a different color ink.

Dependent Variables

The primary dependent variables associated with this task have been the differences in RT and accuracy between incongruent trials and congruent trials. Often termed a "conflict effect" or "executive control effect," these differences are sometimes calculated as a subtraction of congruent RT (or accuracy) minus incongruent RT (or accuracy). With regard to trial-by-trial congruency effects, primary dependent variables of interest include contrasts between the RT for each of the four types of congruency pair data. For example, "conflict adaptation effects" have been previously calculated as [iC - cC] + [cI - iI] (Kerns et al., 2005).

SCWT Variables.JPG

Cleaning Rules

If any of the derived variables listed above are missing, participants should be flagged for exclusion. Additionally, participants who are outliers in the number of trial-by-trial congruency data should be flagged for follow up.

Code/Algorithms

SCWT Stone Scoring.jpg


History of Checking Scoring:

  • David Kaufman independently checked Stone's results in September 2010 and May 2011 and found his results to be accurate.
  • David Kaufman independently checked Stone's trial-by-trial congruency data in June 2011 and found it to contain errors.

Data Distributions

SCWT Mean RT Con.JPG

SCWT Mean RT Inc.JPG

SCWT Mean RT Inc-Con.JPG

ANT-SCWT Corr.JPG

ANT-SCWT Diff Score Corr.JPG

References

Fan J, McCandliss BD, Sommer T, Raz A, Posner MI. (2002). Testing the Efficiency and Independence of Attentional Networks. Journal of Cognitive Neuroscience, 14: 340-47.

Kerns JG, Cohen JD, MacDonald AW, Johnson MK, Stenger VA, Aizenstein H, Carter CS. (2005). Decreased conflict- and error-related activity in the anterior cingulate cortex in subjects with schizophrenia. American Journal of Psychiatry, 162:1833-39.