Stroop experiment

Files needed:

  • Stroop.psyexp
  • StroopKeyPractice.xlsx
  • Stroop.xlsx
  • error.wav

Overview.  The Stroop.psyexp program runs a version of the Stroop color/word task.  Words and nonword strings are presented in one of four colors and subjects must identify the color of the strings.  Sometimes the words are color names congruent with the stimulus color, sometimes they are incongruent color names.  The nonword strings are neither congruent nor incongruent with the color.  Subjects respond by pressing one of four keys.

Details.  Run the program by double-clicking on the Stroop.psyexp file.  This will launch PsychoPy with the experiment timeline loaded.  Run the experiment by selecting “run” from the PsychoPy menu (the green running person).  A dialog box will appear in which the student can optionally enter their name or initials.  Any string entered will become the first part of the name of the data file.

Subjects are to indicate the color of the letter string on each trial as follows: red: z, green: x, blue: period, yellow: slash.  An initial block provides practice with the response assignments (i.e., all congruent trials).  A second practice block provides practice at the task.  There are 4 test blocks containing 36 trials each, with a break between each block.  Each block contains 12 congruent trials (3 of each possibility), 12 incongruent trials (one of each combination of stimulus color (4 possibilities) * incongruent color name (3 possibilities)), and 12 neutral trials.  The lengths of the strings of colored x’s in the neutral trials match those in the incongruent trials.  In other words, the string “XXXX” can appear in red, green, or yellow, but not blue.

Other details of the method can be learned by examining the timeline and the events in PsychoPy.  In cases where attributes of the events are variable, the variables are typically specified in the provided Excel files.

Data analysis.  The data are in a *.CSV file in the “data” folder in the Psych/Lab folder.  Double-click on this file to open it in Excel.  Each row corresponds to a trial.  Entries in the column labeled condition show the condition for that trial. Keyresponse.RT contains the reaction time (in seconds).  Keyresponse.corr codes whether the response was correct (1) or incorrect (0).  The first one (or more) sets of trials might be practice and should not be analyzed.  See the instructions elsewhere for creating a pivot table to summarize the data.