The electric response of the human eye

The present work arose from an investigation of the electrical changes in the human brain, particularly those produced by the exposure of the eyes to a flickering light. Some years ago Adrian & Matthews (1934) found that potential waves, in phase with the flicker, could be recorded from the occipital part of the head. As a rule, the frequency of the occipital waves agreed with that of the flicker, but sometimes it occurred at double the rate and, as this doubling complicated the analysis of the cerebral events, it seemed necessary to find out how it arose and, in particular, whether it arose in the brain or in the eye. The simplest method of attack was to try to record the potential waves generated in the-retina as well as those in the brain. The attempt has been successful to the extent of showing that a double response may certainly arise in the eye, but the more important finding is that the human electroretinogram can be recorded without much difficulty and can give fresh information about the retinal mechanism. What follows is mainly concerned with the potential changes occurring in the eye in response to single flashes of light. Responses to flickering light are described in a later section. The doubling of the cerebral flicker rhythm will be dealt with elsewhere, although, in fact, it was the starting-point of the investigation. Previous work on the human electroretinogram is summarized in a paper by Cooper, Creed & Granit (1933). It has been established that the response of the human eye has the same general form as that recorded from other vertebrate eyes, isolated or in situ, or from the exposed retina, but technical difficulties have prevented any further study of it. One of the chief difficulties has been that eye movements are hard to avoid and give rise to potential changes resembling those of the electroretinogram. In the present experiments they have not caused much trouble, partly no doubt because the subject learnt to control them, but mainly because of the shortness of the period of iliumination. As a rule the stimulus was a flash lasting not more than 1/20 sec., and no serious attempt was made to record with exposures lasting more than a second. Thus the inconveniences of a wandering base-line have not been serious.