A human performance experiment was conducted to investigate pixel parameter requirements for three types of flat-panel display images: an alphanumeric character, an oscilloscope waveform, and a real-world image. Subjects performed similarity judgments between an extremely high-quality image and an image composed of different levels of anti-aliasing and pixel width-plus-pixel separation (pitch). It was found that the effect of pitch had greater influence on perceived image quality for the alphanumeric character and oscilloscope waveform than for the real-world image. The results of this research provide empirical evidence showirg that the pixel pitch requirements for flat-panel systems that are used to display binary, high-contrast images (such as text and waveforms) will be more stringent than for low-contrast pictorial images. The three levels of grey-scale anti-aliasing investigated were found to improve image quality for only the binary, high-contrast images.

The human eyes are always moving. Even during periods of fixation when visual information is acquired, a persistent jittering of the eyes (ocular drift) is occasionally interrupted by small rapid gaze shifts (microsaccades). Though much has been learned in the last 20 years about the perceptual roles of fixational eye movements, little is known about the consequences of their active control for fine pattern vision and depth perception. Using custom techniques for high-resolution eye-tracking and precise control of retinal stimulation, this dissertation describes three studies that investigated the consequences of controlled fixational eye movements for visual perception of fine patterns in two and three dimensions. The first study addresses whether fixational eye movements are controlled to meet the needs of a demanding visual task and their contributions to visual acuity. We show that in a standard acuity test, humans actively tune their drifts to enhance relevant spatial information and control their microsaccades to precisely place stimuli within the foveola. Together these eye movements contribute 0.15 logMAR to visual acuity, approximately two lines of an eye chart. The second study addresses the perceptual and computational impact of tuning ocular drift. We show that humans are sensitive to changes in visual flow generated by drifts of different sizes. Changes in sensitivity are fully predicted by changes in effective power of luminance modulations delivered by drift, suggesting that drift acts as a mechanism for controlling the effective contrast of the retinal stimulus. The third study addresses the impact of binocular fixational eye movements on fine depth perception. We show that these movements, specifically the opposing movements of the eyes (vergence), are beneficial for stereovision. In the absence of disparity modulations from fixational vergence, fine depth perception is significantly impaired. The research described in this dissertation advances the field in several fundamental ways by showing that (a) contrary to traditional assumptions, ocular drift is tuned to the demands of the visual task; (b) the precise spatiotemporal structure of the luminance changes from ocular drift predictably impacts visual sensitivity; and (c) stereoscopic vision is a dynamic process that uses temporal disparity modulations generated by fixational vergence. / 2024-02-02T00:00:00Z

The present study was designed to answer the question: WIll stutterers perform differently from fluent speakers on a test of tachistoscopic recognition. It was hypothesized that persons exhibiting overt secondary symptoms of stuttering would demonstrate a visual field preference different from an age-matched group of fluent speakers who have no personal or familial history of stuttering.

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