The work here described attempts to locate anatomically and to clarify the nature of dominant nonlinear operators in the human pupillary system for reflex to light. For this work an apparatus was constructed capable of stimulating both eyes simultaneously and recording the pupil diameter of one eye. Short light flashes were used as the input stimulus, and the maximum change in pupil diameter was chosen as the amplitude of response. Results of the experiments (1) confirmed the loglike dependence of response on input-light-flash energy, (2) demonstrated a dependence of response amplitude on duration between pulses in the double-pulse stimulating situation, (3) established the equivalence of response to double-pulse inputs in the cases of monocular and binocular double-pulse presentations, and (4) determined for the monocular and binocular cases the dependence of response amplitude on the amplitude of the second pulse in a double-pulse presentation. The similarity of results of the monocular and binocular cases suggests that the dominating nonlinear operation occurs after the summation of signals from the two eyes. The dependence of response amplitude on duration between pulses is discussed in terms of its implication of central mechanisms.
FRANK H. BAKER, "Pupillary Response to Double-Pulse Stimulation; a Study of Nonlinearity in the Human Pupil System," J. Opt. Soc. Am. 53, 1430-1436 (1963)