A New Method for Measurement of the Pupillary Light Reflex and the Temporal Relation of Stimuli in Conditioning Pupillary Light Reflex

Abstract

One of the most difficult problems in the experimental study of the conditioned pupillary light reflex is the determination of the precise technique to use in recording the pupillary movement. Up to the present time, two methods have been available : (1) the use of the pupillometer, which could roughly measure the pupillary reflex but not detail of latency, magnitude, and configuration ; (2) the use of photography, but this does not provide a continuous pupillographic curve and besides excepting the infrared photography, the ordinary photography requires high luminosity wihch is disadvantageous to the experiment in conditioning.
The present experiment was made possible by the newly introduced method in which the minute changes of the pupil were automatically and continually recorded. The apparatus consisted of parts for pupillary measurement, its recording and devices for the presentation of stimuli. The constant light was adjusted to illuminate the pupil of the left eye and was reflected so as to be received by a photoelectric cell which was placed in front of the nose and between visual lines directed to a fixation point. The amount of light reflected in accordance with the changing size of the pupil and iris was converted by the photoelectric cell to an electrical charge which was amplified and recorded by an ink-writing oscillograph. To the right eye, the light of the unconditioned stimulus which was isolated from the left eye and the photoelectric cell was presented and its consensual reflex on the left eye was measured.
This study was concerned with time intervals between conditioned and unconditioned stimuli. Seven temporal relations were set up. One of them was the simultaneous presentation of the conditioned and unconditioned stimuli, four were successive conditionings with periods of delay of 1, 3, 6 and 9 seconds respectively, and two tarce conditionings of 0 and 3 seconds, where the du-ration of unconditioned stimuli was 6 seconds throughout.
Good results were obtained in the successive conditioning of 6 seconds and the trace of zero second. Dynamic processes of the response in the period of delay and the latency in the course of the conditioning were observed. The pupillograph derived from this experimental technique provides a way to the study of inhibitiory mechanisms which frequently disturb the formation of the conditioned pupillary reflex.