CNP SCWT

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Revision as of 03:16, 25 June 2011 by Stigge (Talk | contribs) (Task Procedure)

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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

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Task Parameters Table

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Stimuli

Stimuli consisted of two doors simultaneously presented in the left and right sides of a gray screen. Visual reward feedback was an image of two quarters, which appeared in place of the correct door. Visual non-reward feedback was an empty white square, which appeared in place of the incorrect door.

Auditory reward feedback was a cash register sound that lasted approximately 500 ms. Auditory non-reward feedback was a buzzer sound that lasted approximately 500 ms.

A fixation stimulus was a small white square that appeared in the middle of the screen and prompted participants to either "Press" the middle key to begin each trial, "Hold" the middle key to wait for the doors, or select "Left or Right?" once the doors appeared.

Dependent Variables

The primary dependent variables associated with this task have been the total number of trials to criterion during acquisition and reversal conditions (Laughlin et al., 2011). Other dependent variables that may be of interest include the number of reversal errors, mean RT on reversal error trials, and overall change in RT across the final 5 consecutive correct trials in acquisition and reversal conditions.

DRLT Variable Table.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 trials administered for acquisition or reversal conditions should be flagged for follow up.

Code/Algorithms


History of Checking Scoring:

  • David Kaufman independently checked Stone's results in September 2010 and May 2011 and found his results to be accurate.

Data Distributions

References

Laughlin RE, Grant TL, Williams RW, Jentsch JD. (2011). Genetic dissection of behavioral flexibility: reversal learning in mice. Biol Psychiatry, 69: 1109-16.

Robbins TW. (2000). Chemical neuromodulation of frontal-executive functions in humans and other animals. Exp Brain Res, 133:130-138.