I’m having troubles to program an experiment where visual stimuli are presented at a random position for a 60 ms and then immediately replaced by a mask at exactly the same position for the same length of time.
I tried to set different trials with both a stimulus and a mask events and using using variable positions (upper left, upper right, lower left, lower right) randomized once every trial, but that doesn’t seem to help: stimuli and masks positions are randomized independently.
Additionally, I would need to have a fixation cross throughout the whole experiment, and if I program it as different images (followed by stimuli where the screen is not previously erased), I get a flickering effect.
Thanks for your answer. Ideally, the experiment would be like this:
A fixation cross is presented throughout the experiment at the screen center.
Image 1 is presented at a random position, for instance position B (let’s say there are 4 preset screen positions: A, B, C, and D), and after a few milliseconds it’s replaced by a mask at position B.
ISI: blank screen with a fixation cross in the middle.
Image 2 is presented at position C, followed by a mask at the same position.
ISI: blank screen with a fixation cross in the middle.
.
.
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The fixation cross remains at the center of the screen in steps 2 and 4.
For your first question, as far as we know there is not a way to do this.
Regarding the fixation point, can you give me more details on how you have it set up?[/QUOTE]
Hi Monika,
Thanks for your reply! I’m a little bit surprised that an stimulus and a mask cannot be presented at the same random position… The only alternative I could think right now is to construct a list of randomized positions and then to present the stimuli and masks at those previously determined positions. I’m certainly not very happy with this solution… Guess I’ll have to keep working on this…