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Lexical decision experiment

Files needed:

  • LexicalDecision.psyexp
  • LexicalDecisionPractice.xlsx
  • LexicalDecisionTest1.xlsx
  • LexicalDecisionTest2.xlsx
  • error.wav

Overview.  The LexicalDecision.psyexp program runs a lexical decision task with semantic priming.  On each trial of the experiment, the subject is shown a target string of letters that is either an English word or a pronounceable nonword. The target string is preceded by a word that is sometimes semantically related to the string.  Subjects categorize the target as either a word or nonword and respond by pressing one of two keys.

Details.  Run the program by double-clicking on the LexicalDecision.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 user is asked for a conditionfile number.  Enter a 1 or 2 here (see explanation below).  The student can also optionally enter their name or initials in the ‘participant’ field.  Any string entered there will become the first part of the name of the data file.

On each trial, the subject is shown a target string of letters that is either an English word or a pronounceable nonword. The subject’s task is to decide, as quickly as possible, whether the letter string is a word or a nonword. Subjects respond as follows: word=/, nonword=z. Shortly before the presentation of the target string, the subject is shown a prime. The prime is always a word and it sometimes has a meaning that is related to the meaning of the target string (assuming that the target string is a word). The subject does not need to attend to the prime, because the lexical decision is to be made only on the target string. Thus, there are three types of trials in this experiment: (1) nonword trials, where the target is anonword, (2) unrelated word trials, where the target is a word and the prime is unrelated to the target, and (3) related word trials, where the target is a word and the prime and target have related meanings.

After a practice block of 48 trials, subjects serve in 112 trials, with a break offered after every 30 trials.  One half of the targets are words.  Of those, one half are preceded by a related prime.  The target strings are identical for “conditionfile” 1 and 2.  Targets that are in the related word condition for “conditionfile” 1 are in the unrelated condition for “conditionfile” 2, and vice versa.

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.

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