Using confidence inferred from pupil-size to dissect perceptual task-strategy: support for a bounded decision-formation process

Abstract

During perceptual decisions subjects often rely more strongly on early rather than late sensory evidence even in tasks when both are equally informative about the correct decision. This early psychophysical weighting has been explained by an integration-to-bound decision process, in which the stimulus is ignored after the accumulated evidence reaches a certain bound, or confidence level. Here, we derive predictions about how the average temporal weighting of the evidence depends on a subjects decision-confidence in this model. To test these predictions empirically, we devised a method to infer decision-confidence from pupil size in monkeys performing a disparity discrimination task. Our animals data confirmed the integration-to-bound predictions, with different internal decision-bounds accounting for differences between animals. However, the data could not be explained by two alternative accounts for early psychophysical weighting: attractor dynamics either within the decision area or due to feedback to sensory areas, or a feedforward account due to neuronal response adaptation. This approach also opens the door to using confidence more broadly when studying the neural basis of decision-making.