Brain Imaging & Analysis Center

Fixed PPFs, as illustrated in the PPF page, provide a simple and easy way of relaying task information to the subject at appropriately-timed intervals. However, some tasks may require more subject involvement, especially in regards to measuring response time. To create a parameter file that allows for a smooth transition from one task to another based on the subject's response, the rwait stimulus task will be used after each designated task.

The example below illustrates the set-up for a self-paced parameter file. The first task (labelled one), begins at time 0, at the standard position (-1,-1). The duration of the task is 0, or indefinite, since the length is determined by the rwait rather than the stimulus task itself. Therefore, the next command is rwait. This stipulates that ShowPlay is waiting on the subject's response to the previous stimuli. This also begins at the same time as the first task (or whatever limit is imposed upon the subject's ability to respond to the stimuli). The duration will provide a fixed time frame which will automatically time-out the stimuli if the subject does not respond. In the example below, the fixed limit is at 15 seconds.

Following the rwait command is the reset command. This will restart the timing of the parameter file to zero, so all stimulus loaded after the reset will have to be calculated from zero. The reset should also begin at the same time as the rwait (time 0), to allow for an immediate subject response. The duration of the reset will automatically be the same of the rwait. When the rwait times out, so will the reset. To set-up for the next task, follow the reset command with an erase command. The erase will begin as soon as the last command ends (-1), so when subject responds to the First Task, the rwait will end, as will the reset, and the erase will automatically clear the first stimuli. The final step is to put in the next stimulus, Second Task, to begin as soon as the erase ends (-1). In the example below the second task follows the pattern of the first task in creating a subject-response stimulus, but it can easily be substituted for a fixed time-frame by changing the duration of the task and not including the rwait and reset commands.

First Task	     	      1       1       0          0       -1 -1
rwait                         0       0       0        15000
reset                         0       0       0
erase                         0       0      -1
Second Task                   2       0      -1          0       -1 -1

See Also:
ShowPlay Tutorial, ShowPlay Home, ShowPlay Manual, CIGAL Home, CIGAL Manual,