The program LEXICAL runs a typical lexical decision experiment. 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 subject's task is to decide, as quickly as possible, whether the letter string is a word or a nonword. The response is indicated by pressing the / key if the string was a word, and the Z key if the string was a nonword. 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 a nonword, (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.
If the response was too slow or incorrect then a short tone is presented. Raw data from the experiment are placed in
the file DLEX.DAT. An analysis program (LEXANAL) reads the data file and computes means and standard
deviations of the reaction times for correct responses in each of the conditions. The output of the analysis is placed in
the file ALEX.ANL.
Running the experiment
To run the experiment, just type LEXICAL and hit "Enter". After entering a random number, you will be asked to enter your "condition number". Enter either a 1 or 2, whichever was assigned to you by the instructor. The condition number determines the particular words and nonwords that will be presented. When asked to "Press any key to begin", pressing the 'P' key will allow you to change various parameters that determine the design of the experiment and the timing of trial events. Pressing a key other than 'P' will cause the program to proceed immediately to the first block of trials. The parameters that can be safely changed are listed below, along with their probable default values.
1. duration of fixation plus (msec):
(default=1000)
2. duration of prime word (msec):
(default=700)
4. inter-trial interval (msec):
(default=250)
6. Duration of error tone (msec):
(default=500)
7. Interval between prime offset and target onset (msec):
(default=50)
11. Y location of stimuli (between 0 and 32000):
(default=16000)
12. X location of central fixation point:
(default=16383)
17. minimum allowed RT (msec):
(default=100)
18. maximum allowed RT (msec):
(default=900)
19. target duration (msec):
(default=1000)
Note. The target strings are identical for "condition numbers" 1 and 2. Targets that are in the related word condition
for "condition number" 1 are in the unrelated condition for "condition number" 2, and vice versa.
Analyzing the data (You will need analysis program available below)
Simply type LEXANAL and hit "Enter" from the directory in which the experiment was run. When asked "Number to trim from each end" the user has the option to exclude the desired number of extreme reaction times from the analysis. Hitting "Enter" will not exclude any data. To view the means from each condition TYPE or PRINT the file ALEX.ANL. (Means are shown in the following order: Nonword, Unrelated Word, Related Word.) If you want to view the raw data, TYPE or PRINT the file DLEX.DAT. Each time that LEXICAL is run, the program will destroy all previous DLEX.DAT data files. Each time that LEXANAL is run, it will destroy all old ALEX.ANL files. Therefore, be sure to look at the data before the experiment is run again. in.