I am trying to put together an affective startle modulation task. For the task, participants are simply asked to watch a series of pictures that are presented on the computer screen while wearing headphones. The pictures are drawn from three stimulus lists, with 1/3 of the pictures depicting neutral scenes, 1/3 positive scenes, and 1/3 aversive scenes. Pictures are shown for 6 seconds, with a variable intertrial interval. A startle stimuli is presented at 1 of 3 time-points during the picture viewing (1.5 seconds, 4.5 seconds, or 7.5 seconds following picture onset).
I’ve put together 3 sound files of equal length, but with the short burst of white noise placed at different points relative to the onset of the sound-file. My task is set up so that I start the sound file, then present the picture file for six seconds, followed by a blank screen (so that the 7.5 second sound file presents the startle stimuli after the picture is erased from the screen).
I have 3 stimulus lists for the neutral, positive, and negative pictures, and one stimulus list for the sound files. My issue: I’d like to randomly pair the picture with the sound file, so that each picture is only shown once during the study, and is randomly paired with one of the sound files. Although I can easily put together a version of the study using stimulus lists that pairs the same picture with the same sound file (and then randomly presents the pictures in different orders across participants), I can’t figure out how to put together a version of the task that allows me to randomly pair the pictures and sounds for each participant, while only presenting each picture one time. Any thoughts would be appreciated! For the record, I’m recording the startle responses (and timing signals from superlab) with Biopac psychophysiology equipment.