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Michael F. Fry, Sarah Moore, Michael A. Webster; Blur thresholds following blur adaptation. Journal of Vision 2004;4(8):488. doi: 10.1167/4.8.488.
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Adaptation to a blurred image causes a physically focused image to appear sharper. We tested whether this phenomenal sharpening also results in concomitant changes in the legibility of spatial information in the image. Observers adapted by reading passages of text that were slowly scrolled upward (0.15 deg/sec) within a 4-deg field presented on a monitor, with ∼3 lines of text per degree. On different sessions the text images were Gaussian-blurred over 6 levels ranging from the original focused text to blur levels that were roughly twice the blur threshold for reading. Following 2 min of adaptation at each level, subjects were presented a series of test images composed of random letter strings with a random common first name at the center, and responded whether the name was male or female. A staircase varied the blur level in the test images to determine the acuity limit. In separate measurements a single name was presented and subjects instead reported whether the text appeared focused or blurred. Prior adaptation to blurred text strongly biased the perceived blur in the text, with greater effects for moderate than strong blur. Adaptation also produced weak but significant improvements in the blur thresholds for reading. In contrast to the changes in perceived focus, these thresholds showed a roughly linear trend with adaptation level, as confirmed by a regression analysis of the thresholds vs. adapting blur level. These results support previous measurements of acuity changes following exposure to optical blur (e.g. Mon Williams et al., P. R. Soc. Lond. 1998) in suggesting that adaptation to blur can affect not only subjective image quality but also visual performance.
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