Moving dots- clustered dots

Support
1

Hi Chris,
I’ve been working on an experiment using the moving dots stimulus, where on each trial the dots move in a different direction. On the first trial, this works well. But on subsequent trials the dots are often clustered at one side of the stimulus such that if the field is smaller than the screen there is a semi-circle of dots coming from one end of the field. This disperses as the dots continue to drift, but is initially problematic. Is there a stimulus “reset” that needs to be done at the beginning of each trial?
Thanks,
Lindsey.

2

Hi Lindsey,

I don’t know why that would be happening. Can you send me an experiment that demonstrates the problem?

Thanks,
Chris

3

Hi Chris,
Here is the experiment I have been working on. I am also including a
variable set. This needs the pulse generator to make it progress through
the task states, but otherwise should just run. The issue starts on the
second trial (you can reduce the reaction time variable to get there
sooner).
Lindsey.

4

Hi Lindsey,

Sorry, I didn’t receive the experiment. Can you try sending it again?

Thanks,
Chris

5

Sorry- sometimes it works without compressing, sometimes not.
Here’s the compressed version.
Lindsey.

6

Thanks, I got it this time. I see the issue, but I’m not yet sure what the cause is. Let me investigate some more and get back to you.

Chris

7

Hi Lindsey,

You need to call stop_dynamic_stimulus to reset the dots between trials. In state StimOn, do this:

if (doDotsDiscrim) { 
    stop_dynamic_stimulus (targetDots)  // This is new
    live_queue_stimulus (targetDots)
    play_dynamic_stimulus (targetDots)
    report('Queuing dots- contrast is $tGratingContrast')
}

Also, I see that your experiment is dequeuing and re-queueing the dots mid-trial, which makes it look like the dots stutter. I don’t know if that’s intended, but I thought I’d point it out.

Cheers,
Chris

8

Thanks!
Lindsey.