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.
The pupil oscillates in synchrony with a slow beat produced by adding two lights flickering at slightly different frequencies. This behavior shows that nonlinear processes are present within the pathway. To localize these processes, a light of one frequency was presented to one eye, while a light of a different frequency was presented to the other. No pupil oscillations were seen in response to the beat in these dichoptic conditions, but when both lights were superimposed and presented to the same eye a powerful pupillary response was produced. We conclude that the nonlinearity giving rise to the pupil's beat response occurs before the pathways from the two eyes join and hence is neural rather than muscular in origin. Furthermore, the lack of a pupil response in the dichoptic conditions suggests that the signals from the two eyes may combine linearly.
The detectability of a brief color shift towards red or towards green of a foveally viewed yellow target is less by 25% if the observer is uncertain as to the direction of the color shift. This result matches a prediction of the theory of signal detectability: When signal parameters become uncertain, detectability declines.
This study aimed to answer the question of how to design a visual warning signal that is most easily seen and produces the quickest reaction time. This is a classic problem of bionic optimization—if one knows the properties of the receiver one can most easily find a suitable solution. Because the peak of the spatio-temporal contrast sensitivity function of the human visual system occurs at non-zero spatial and temporal frequencies, it is likely that movement enhances the detectability of threshold visual signals. Earlier studies employing extended drifting sinewave gratings bear out this prediction. We have studied the ability of human observers to detect threshold visual signals for both moving and stationary stimuli. We used discrete, localized signals such as might be employed in aerospace or automotive warning signal displays. Moving stimuli show a superior detectability to non-moving stimuli of the same integrated energy. Moving stimuli at threshold detectability are seen faster than non-moving threshold stimuli. Under some conditions the speed advantage is over 0.25 seconds. Similar advantages have also been shown to occur for suprathreshold signals.
We employed vertical sinusoidal test gratings to search for spatial adaptation to lower-case text presented on a standard video display terminal. The parameters of the contrast sensitivity test were selected on the basis of waveform analysis of horizontal spatial luminance profiles of the text. We found that subjects exhibited a small (4-5 dB), but significant, frequency-specific spatial adaptation consistent with the frequency spectrum of the stimulus. The theoretical and practical significance of this finding is discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.