Abstract

Data on the dark adaptation of three subjects were gathered. All were given the same pre-exposure and testing conditions and threshold measurements taken for 40 min at each experimental session. Each subject served in 12 sessions spread over a period of 11 months, and two dark adaptation curves were obtained at each session. The effect of obtaining two curves per session, morning versus afternoon conduct of the sessions, and of changing experimenters was investigated, and, except for one minor difference, no statistically significant effect was found to result from these factors.

The data showed that the variability of threshold measurements changed during the course of 40-min dark adaptation. It began at a given value and declined in magnitude toward the end of cone adaptation. At the time of the cone-rod transition the variability of two of the subjects showed a marked increase and it remained at a relatively high level for several minutes, gradually becoming smaller. After about 20 min the variability reached a minimum, stable value and stayed around this value for the remainder of dark adaptation. An explanation is offered to account for this result. Another result was that the magnitude of the variability showed inconsistent changes during the progress of the experiment, brought about by aberrant curves that were obtained from time to time. There seems to be no ready explanation for the occurrence of such curves.

© 1955 Optical Society of America

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