Biomedical subjects
Publications and source records attributed to P Mulvanny.
A portable microprocessor-controlled instrument automatically measured the static and dynamic contrast sensitivity functions (CSF's) of 265 observers for a normal population at the Dayton Air Fair and Air Force Museum. Repeat measures for six observers taken 6 months later show small, nonsystematic differences from original measurements. Median values of contrast sensitivity as well as regions encompassing 75 of 90% of our sample are shown.
The role of sustained and transient mechanisms in pattern and flicker perception has been examined in two discrimination experiments. In the first, observers were required to analyze the temporal or spatial properties of a stimulus that highly stimulated either sustained or transient mechanisms. The results were only partially consistent with a model identifying sustained mechanisms with pattern perception and transient mechanisms with flicker perception. In the second experiment a subthreshold summation paradigm was used to explore interactions among those mechanisms that encode the temporal and spatial properties of a stimulus. The effect of a subthreshold temporal-frequency change on discrimination performance could not be explained by models in which temporal-frequency and spatial-frequency changes are evaluated separately and then combined.
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The contrast sensitivity of patients undergoing hemodialysis therapy for chronic renal failure was measured and compared to that of a control group. Both contrast sensitivity and visual acuity of the patients were reduced. Ocular and fundoscopic exams revealed differences between the patients and controls, but these differences could not fully account for the visual deficits. The visual deficits could be expected to cause reduced visibility under everyday conditions for the patients.
Moving visual phantoms look like real gratings and generate movement aftereffects as do real gratings. Three experiments have been carried out to test whether phantoms resemble real gratings in other ways. Changes in the spatiotemporal frequency of an inducing grating effect the minimum contrast at which it will induce phantoms, but only insofar as the changes affect the visibility of the inducing gratings. Changes in the areal extent of the inducing grating and in the extent of the gap across which phantoms must be induced alter the visibility of the phantoms but, again, only to the extent that the changes affect the visibility of the inducing gratings themselves. Phantoms induced by high-contrast gratings may be cancelled by gratings of near-threshold contrast when the latter are presented 180 degrees out of phase with the inducing gratings. It is concluded that the appearance of phantoms is governed solely by the detectability of their inducing gratings, but that the effects of phantoms on pattern-sensitive channels are not the same as are the effects of real gratings. The pattern characteristics of phantoms thus do not represent a spread of energy from inducing to phantom regions of visual space or their neural representations.
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