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J.A. Potter, N.C. Strang, D. Whitaker; Temporal Integration of Astigmatic Blur Information . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5643.
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Purpose: Dynamic accommodation tracking in the presence of astigmatic defocus allows both the in–focus and defocus information contained within an image to vary over time. This type of tracking has the potential to provide additional in–focus information to the visual system and, as a result, improve visual resolution. To test this hypothesis we measure visual resolution in simulated astigmatic blur conditions, with the magnitude of astigmatic blur being temporally modulated over a range of astigmatic blur intervals. Improvement in visual resolution with an increased range of astigmatic blur would support the integration of visual information over time hypothesis. Methods: Four fully corrected subjects participated in a 3–AFC method of constant stimuli paradigm where they were asked to identify one of three letters (K, R and X). The stimuli were subjected to various amounts of Gaussian blur along the horizontal and vertical meridian. On any trial, the stimuli were randomly presented to the subjects at one of six presentation levels. Each blur interval oscillated at a temporal frequency of 2Hz around the circle of least confusion with the smallest interval presenting the stimuli at the circle of least confusion and the largest oscillating the stimuli across the full interval i.e., from the most horizontally to vertically blurred meridian. A further control experiment was carried out in which astigmatic stimuli from different sections of astigmatic blur interval were presented statically, to ensure that one particular astigmatic blur section was not responsible for any improvement in visual resolution. Results: Psychometric functions found that all subjects exhibited a progressive improvement in letter resolution with increasing dynamic blur interval (F5,15=9.192, p=0.0004). The magnitude of the improvement was significantly reduced in the control experiment. Conclusions: The improvement in visual resolution with increased astigmatic blur interval provides evidence that in–focus sections of a modulating astigmatically blurred image can be integrated over time to improve visual resolution.
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