Graded reward based on how accurately a stimuli is touched

Problem: During the training for getting animals to touch stimuli on a touch screen, animals get rewarded for touching a single circle. I would like to now give an extra reward for when animals touch closer to the center versus the outer edge of the circle. So an animal will get reward for touching within the stimulus, but get even more reward for accurately touching towards the center of the stimulus.

I'm using the adapters: CircleGraphic() combined with SingleTarget(touch_)

I'm curious if anyone has done a similar thing with any of their stimuli? I can imagine a possible path forward where I introduce a second smaller circle graphic (that's the same color) inside the other and change to using MultiTarget(touch_) adapter, then connect a separate error_code for each stimuli which activates a second goodmonkey(). But im curious if there is anyway to adjust stimuli thresholds to do something with a single target stimulus.

So far when I've tried to manipulate the target touch threshold it seems to only adjust the area outside of the stimulus, not allowing that threshold area to be smaller within the stimulus.

I do not understand your last sentence. SingleTarget and CircleGraphic are independent; you can set the threshold window to any size that you want and it can be either larger or smaller than the circle size. If you assign a CircleGraphic object as a target to SingleTarget, the threshold window is initialized to the size of the circle, but you can change it afterward as you want.

Currently, MultiTarget uses the same window size for all its targets, so what you described cannot be done with MultiTarget. You just have to use multiple SingleTarget around the circle. See the attached example.

By the way, I do not think this trick will help the animals learn to touch the central area. What they need is visual feedback of the touched location. It will be more effective if you just use multiple concentric circles of different colors and show the touched circle again during reward.