Pupillary contraction and dilation in light and darkness.

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Abstract
The latencies of pupillary contraction and dilation and the nature of the responses of the pupil to light and darkness were determined under two types of exptl. procedure using high-speed photography with infra-red illumination. One exptl. procedure involved contraction immediately followed by dilation; the second procedure determined one latency at a time after long adaptation to either light or darkness. Ten subjects varying in age from 21 to 29 were used under the first conditions and 5 of the same subjects were used under the second. The results show that when the pupil is in a state of activity, either contracting or dilating, both the contraction and dilation latencies are longer than when the pupil is stable immediately before the onset or cessation of light. The latency for contraction of the stabilized pupil was found to be 0.175 sec., for dilation 0.180 sec.

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