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Rapidly switching priors by context in decision making for a single visual detection task

Zhaoping Li

Department of Computer Science, UCL , UK

I show that human subjects can change their priors rapidly in a trial by trial bases for the same visual detection task within a single experimental session. The subjects were asked to answer, yes or no, for whether there is a target bar in the center of a brief visual display. There may or may not be some contextual bars of particular spatial configurations and contrast presented near the target bar. The subjects were informed that the contextual bars were irrelevant to their task. We observed that the probability of the "yes" response depends not only on the contrast of the target presented, but also depends on the contextual stimulus. The data indicate that the subject's responses arised from a Bayesian decision making process, and that their prior probability for expecting the presence of the target is determined by the contextual input. As the context randomly changed from trial to trial, our data indicate that the subjects can rapidly switch, from trial to trial, between different priors determined by different contextual input.