Millisecond Forums

Hi,

Sorry I'm pretty new to Inquisit so forgive me if these are naive questions:
I've been trying to figure out a way to randomize the location of a grey solid circle with the change of the images for each trial. Basically, in each trial, a subject will see a negative or neutral image, and there should be a grey circle showing on top of that image. The location of the grey circle is not pre-determined, but randomized for each subject and for each image within a range. The circle will always need to present within the frame of the image (size 640*480 in the center of the screen). The location of the circle should be fixed for each image (because the images repeat 3 times within a block), such that each unique image has a circle overlaying on the exact same spot for that image. But the location of the circle across images should be randomized (not likely to be the same). Also the subject will respond by pressing either the left or right arrow button to indicate whether the grey circle locates at the right or left side of the image for each trial. So we want a random half of the images in each condition (negative or neutral) have the circle on the left and the other half in each condition on the right to ensure counterbalancing. The stimuli duration is fixed, so no matter they respond or didn't respond, the trial should proceed. But it would be nice to record their accuracy. So ideally it would be great to know how whether the circle is on either side of image and compare that to the key press.

So there really are two parts to this question:
1. how to make two stimuli "covary"?
2. how to "remember" or detect the circle location on each image and record their accuracy?

Hope I describe the question clearly. Thanks for the help in advance!!!