There is an interesting feature in the specification of mouse/touchscreen input. You can cause the rectangle corresponding to the click region be determined by the (possibly varying) size and shape of the visual stimulus.
What I don’t see is any way to use this method with more than one active click region–to do that, it appears necessary to specify the height, width, and center of each click region manually and as fixed regions.
It seems to me that when there are mouse/touchpad inputs defined when a visual event is set up, there should be an option to associate the coordinates of that event with a certain input so that it would linger until (1) the display was erased, (2) a new association is made to that input, or (3) the end of the trial (maybe you could make a case for allowing it to linger beyond the trial).
Suppose you’ve defined four mouse/touchscreen input regions called ma mb mc and md, defined to correspond to the coordinates of the visual stimulus. You then display a set of visual stimuli, sa, sb, sc, and sd at various points on the screen, keeping the first three invisible and not erasing the display. Now you want the subject to choose one of the four by clicking or touching it, so inputs ma, mb, mc, and md are correct responses for sd. But what is “the” visual stimulus? There are (from the subject’s and experimenter’s point of view) four different ones on the screen. However, by the time you have put sd on the screen, it is too late to tie the response region to the coordinates of sa, sb, or sc.
So, the new feature suggestion is that it be possible to associate a certain mouse input region with a visual stimulus for later use during the trial. When defining sa, you would say “use coordinates with input ma”, and similarly with sb:mb, sc:mc, and sd:md. This is independent of specifying the correct choice: in the above scenario, for events sa-sc, “the subject must not respond” would be the correct choice; for event sd, all of ma-md would be correct choices. Then, as each of the four stimuli gets displayed, its coordinates would be saved in one of the mouse input regions, essentially building a possibly very complex clickable array in real time.
What about overlaps? I don’t know. What do you do about this with manually defined clickable regions? I’d say, just do the same thing.
As always, if there is already a way to do this, that would be great.