THE EFFECT OF OXYGEN DEPRIVATION ON THE RELATION BETWEEN STIMULUS INTENSITY AND THE LATENCY OF VISUAL AFTER-IMAGES

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Abstract
The effect of O2 deficiency on the latent time of the "tertiary" visual after-image was measured in a low O2 chamber over a wide range of stimulus intensities. 9 expts. were performed on 3 trained observers. In normal air, there is an inverse relationship between the latent time of the after-image and the intensity of the stimulus; a reduction of the intensity of the stimulus prolongs the latency of the after-image. Anoxia prolongs the latency of the after-image. This effect is consistent with the apparent dimming of the visual field which occurs during oxygen deprivation. The magnitude of the increase in the latent time during anoxia is inversely related to the intensity of the stimulus. During O2 deprivation, the curve relating the latent time of the after-image to the logarithm of stimulus intensity is translated horizontally to the right on the intensity axis. This displacement is in the same direction and of the same order of magnitude as in the case of the curves relating foveal visual acuity and intensity discrimination to the logarithm of stimulus intensity. The data are not sufficiently precise to rule out the possibility of a slight vertical translation as well. The complete recovery of the latent time upon adm. of O2 may require up to 50 min., depending upon the degree and duration of the antecedent oxygen deprivation and other factors. The apparent brightness of the visual field, and light thresholds, is restored to normal within 3-4 min. Consequently, the factors underlying the apparent dimming of the stimuli cannot be the only ones responsible for the prolongation of the latent time of the after-image.