Role of Brightness Contrast and Brightness Contrast-Reversal in Illusory Contour Formation

The effects of artificial pupil size and the effects of a power lens upon the relative prominence of illusory contour were evaluated. The perception of illusory contour was facilitated by conditions associated with increased retinal blur and brightness averaging. This was true whether the blur and averaging were achieved using a large artificial pupil or a power lens. The effects of power lens and the effects of artificial pupil size upon the occurrence of brightness contrast and brightness contrast-reversal (or assimilation) were also investigated. Brightness contrast was changed to brightness contrast-reversal by using either a power lens or a large artificial pupil. The occurrence of vivid illusory contour under conditions found conducive to brightness contrast-reversal was interpreted as evidence that contrast-reversal was more crucial in illusory contour formation than brightness contrast.

Visual Significance of Pupillary Response to an Auditory Task

Subjects simultaneously performed visual and auditory detection tasks. Pupillary dilation accompanies increased cognitive load such as that caused by the auditory tasks. Errors in the visual task increased when the auditory task became more difficult. The increase was greater when the effects of pupillary dilation were blocked by an artificial pupil.

Effect of Artificial Pupil Size on Recognition Threshold

Recognition thresholds for neutral and taboo words increased with a decrease in artificial pupil size for 3 Ss. Under a fully dilated condition without artificial pupils, there was a slight increase in recognition threshold. No differences were observed between neutral and taboo conditions. These results support the suggestion that pupil size may be a plausible mechanism in perceptual defense.