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M. Kwon, G. E. Legge; Spatial-Frequency Bandwidth Requirements for Letter and Face Recognition in Central and Peripheral Vision. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5169.
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It is well known that object recognition requires spatial-frequency bandwidths exceeding some critical value, e.g., 2-3 cycles per letter (cpl) and 8-16 cycles per face (cpf). People with central scotomas who rely on peripheral vision have substantial difficulty with reading and face recognition. Deficiencies of pattern recognition in peripheral vision, such as crowding, might result in higher bandwidth requirements, and may contribute to the functional problems of people with central-field loss. Here we asked whether there is any difference in spatial-bandwidth requirements in central and peripheral vision (10° in the lower visual field) for both letter and face recognition.
The stimuli were the 26 letters of the English alphabet and 26 celebrity faces. Each image was blurred using a low-pass filter in the spatial frequency domain (3rd order butterworth filter). Critical bandwidths (defined as the minimum low-pass filter bandwidth yielding 80% accuracy) were obtained with two procedures: by measuring recognition accuracy as a function of image size with a fixed bandwidth in cycles per degree, and by measuring recognition accuracy as a function of bandwidth in cycles per image with a fixed image size. In each trial, subjects were presented with a filtered image for 150ms and required to choose from among the 26 alternatives.
Data from 13 normally-sighted subjects showed that critical bandwidths were significantly larger in the periphery than fovea for both letter and face recognition (1.15 cpl at fovea vs. 1.39 cpl at periphery for letters; 4.29 cpf at fovea vs.7.68 cpf at periphery for faces). The two different procedures yielded approximately the same results. We also observed that high levels of object-recognition accuracy were possible with lower bandwidths than previously reported. This difference was likely due to methodological differences.
Our results show that the spatial-frequency-bandwidth requirements in peripheral vision are larger than central vision. This difference may contribute to the reading and face-recognition difficulties of people with central-field loss.
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