Abstract

That human pupils react to changes in luminance, color, or form raises questions about how the retinal image is processed at the pretectal level. We report that pupil responses to spatial patterns, such as those to luminance or color, are composed of transient and sustained constriction components. Transiency and sustainedness are evidenced in the response waveforms to different spatial frequency gratings. Generally, the waveform is transient (at onset and offset) for 0.14 to 1.9 cpd gratings and sustained for 1.9 to 7.32 cpd gratings. Because the latency for high frequency responses is longer than that for low frequency responses of nearly identical amplitude, the responses are likely mediated by different processes. Furthermore, amplitude-contrast functions can be modelled as a linear sum of a process that saturates at low contrast and a process that varies linearly with contrast. The nonlinear process mostly accounts for results in low frequencies, whereas the linear process accounts for results in high frequencies. We conclude that pupillary constrictions evoked by spatial stimuli are mediated by magnolike and parvolike visual neurons.

© 1992 Optical Society of America