The program PRECUE runs a version of a Posner precuing paradigm. On each trial, two boxes will appear--one to each side of a central fixation cross. The subject must press the correct one of two keys in response to the appearance of an 'X' in one of the two boxes. If the X appears in the left box, the Z key must be pressed; if the X appears in the right box the / key is correct. The correct key should be pressed as quickly as possible. Before presentation of the stimulus, the subject will receive one of three different types of hints: (1) a VALID cue, (2) an INVALID cue, or (3) a NEUTRAL cue. The cue will be in the form of one or both of the boxes flickering. If both boxes flicker, then no information is provided by the cue--that is a neutral cue. If one box flickers, then it is very likely (80%) that the stimulus will appear in that box. Thus, you should prepare to make the response to that stimulus. But, some of the time (20%) the cue will be misleading and the stimulus will actually appear in the other box (invalid trials). On those trials, just like the other trials, you should press the key that corresponds to the stimulus (the 'X') that is presented. Since you can't tell whether a cue is valid or invalid (until after the stimulus appears), you should assume that the cue is valid (because it is most of the time). If you assume that the cue is valid then that will help you minimize your reaction times.
If the response was incorrect, or if no key was pressed, or if the latency was less than 100 milliseconds, a short tone is
presented. Each of the three trial types (Valid, Invalid, Neutral) are presented at three different cue-to-stimulus
intervals (the delay between the flickering of the box(es) and the appearance of the stimulus X). Raw data from the
experiment are placed in the file DPRECUE.DAT. An analysis program (PRECANAL) 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 APRECUE.ANL.
Running the experiment
To run the experiment, type PRECUE and hit "Enter". 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 begin the first trial immediately. The parameters that can be safely changed are listed below, along with their probable default values.
1. Total number of trials per block:
(default=60)
2. Total number of blocks per session:
(default=6)
4. Number of practice blocks:
(default=1)
5. Inter-trial interval (msec):
(default=500)
6. Duration of error tone (msec):
(default=500)
7. Interval between display onset and cue (msec):
(default=1000)
8. Number of trials per block with NEUTRAL cue:
(default=12)
9. Number of trials per block with VALID cue:
(default=36)
10. x location of stimuli
(default=16000)
11. y location of fixation point
(default=16000)
12. Color of target X (white, red, green, blue, yellow):
(default=1)
13. Cue-stimulus interval # 1 (msec)
(default=200)
14. Cue-stimulus interval # 2 (msec)
(default=400)
15. Cue-stimulus interval # 3 (msec)
(default=800)
19. Color of boxes (white, red, green, blue, yellow):
(default=5)
20. Maximum allowed RT (msec):
(default=3000)
Note. The order of conditions within a block, and the locations of the stimuli are determined randomly.
Analyzing the data (You will need analysis program available below)
Simply type PRECANAL 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 APRECUE.ANL (i.e., issue the command: TYPE APRECUE.ANL "Enter"). If you want to view the raw data, TYPE or PRINT the file DPRECUE.DAT. Each time that PRECUE is run, the program will destroy all previous DPRECUE.DAT data files. Each time that PRECANAL is run, it will destroy all old APRECUE.ANL files. Therefore, be sure to look at the data before the experiment is run again.