No abstract

An infra-red pupillometer was used to record pupillary unrest, or hippus, on three observers at various steady illuminance levels. Frequency spectrum analysis of pupillary oscillations shows that, in logarithmic units, amplitude per unit frequency is a decreasing linear function of frequency, and that amplitudes are reduced at higher illuminance levels. Hippus was then recorded for one observer in the presence of extreme discomfort glare. The resulting frequency spectrum is very similar to spectra obtained in high luminance non-glaring conditions. It is concluded that pupillary hippus is unlikely to be a factor in the genesis of the discomfort felt under conditions of glare.

Saccadic suppression is a decline in detectability of a weak flash presented during a saccadic eye movement. We examined the hypothesis of Matin [Psychol. Bull. 81, 899 (1974)] that saccadic suppression may be due to increased stimulus uncertainty during the saccade. Uncertainty could arise from variability and inhomogeneities in the visual frame of reference translation that must accompany a saccade. We measured an average 0.6-log-unit suppression for a brief foveal 1 degree flash in a light-adapted detection task. Receiver-operating-characteristic (ROC) slopes for flash detection during saccades, compared with those when fixating, were reduced, indicating the presence of increased uncertainty. The magnitude of this uncertainty change was estimated and found to be consistent with that required to account for the measured detectability decline. When a flashed pedestal was employed to reduce the effect of uncertainty, there was no saccadic suppression and no ROC slope change. Also, spatially separate flashed markers, intended to reduce uncertainty, led to a significant reduction in saccadic suppression for one of two subjects. Our results are consistent with the hypothesis that a saccade leaves the observer with increased uncertainty as to which subjective visual direction to attend for a stimulus of fixed retinal locus. The magnitude of this uncertainty change can account fully for the saccadic suppression measured.