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Leila Montaser-Kouhsari, Marisa Carrasco; Perceived spatial frequency varies as a function of location in the visual field. Journal of Vision 2008;8(6):432. doi: 10.1167/8.6.432.
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Goal: Performance in a visual acuity task (Landolt-square) is better on the horizontal than on the vertical meridian and for the isoeccentric locations, it is better at the South than the North (Carrasco et al., 2002). In addition, performance in a visual short memory spatial frequency judgment task is better on the horizontal than on the vertical meridian (Montaser-Kouhsari & Carrasco, VSS 2007). Given that performance in these two tasks is related to spatial frequency, here we investigated whether perceived spatial frequency varies as a function of the stimulus location.
Method: Observers performed a spatial frequency judgment task at 4 different isoeccentric locations of the visual field (North, South, East and West). Each block started with the presentation of a 7-cpd Gabor patch (standard) at the center of the display for 30 s. In each trial, a Gabor patch (test) was presented for 100 ms at 6 deg of eccentricity. The spatial frequency of the test stimulus ranged from 6.6 to 7.4 cpd. Observers were asked to report which of the two Gabors, the standard or the test, had a higher spatial frequency. We obtained psychometric functions for perceived spatial frequency for each location.
Results: Perceived spatial frequency varied as a function of location. The point of subjective equality (PSE) was lower than the standard in the East and West locations but higher than the standard in the North and South locations. These results suggest that differences in perceived spatial frequency at different locations may be related to performance differences across the visual field in spatial resolution tasks (Carrasco et al., 2002). Moreover, perceived spatial frequency may mediate performance differences in visual short term memory tasks across the visual field (Montaser-Kouhsari & Carrasco, VSS 2007).
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