A Computational Model of Pupil Dilation

We present a system-level connectionist model of pupil control that includes brain regions be- lieved to influence the size of the pupil. These include parts of the sympathetic and parasym- pathetic nervous system together with the hypothalamus, amygdala, locus coeruleus, and the cerebellum. Computer simulations show that the model is able to reproduce a number of important aspects of how the pupil reacts to different stimuli: (1) It reproduces the char- acteristic shape and latency of the light-reflex. (2) It elicits pupil dilation as a response to novel stimuli. (3) It produces pupil dilation when shown emotionally charged stimuli, and can be trained to respond to initially neutral stimuli through classical conditioning. (4) The model can learn to expect light changes for particular stimuli, such as images of the sun, and produces a ‘light-responses’ to such stimuli even when there are no change in light intensity. (5) It also reproduces the fear-inhibited light reflex effect where reactions to light increase is weaker after presentation of a conditioned stimulus that predicts punishment.