Christof Koch and Colleagues Find Pupil Dilation Marks Decision Making

Christof Koch, the Troendle Professor of Cognitive and Behavioral Biology and Professor of Computation and Neural Systems, and his colleagues, have found that changes in pupil diameter correspond to the moment when a simple decision is made. The pupil, which is about 2 mm wide in bright light, dilated by as much as 1 mm at that moment--a change that, in theory, could be noticeable to a casual observer. [Caltech Press Release]