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Jared Abrams, Marisa Carrasco; Visual performance fields in noise. Journal of Vision 2010;10(7):1367. doi: 10.1167/10.7.1367.
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© ARVO (1962-2015); The Authors (2016-present)
Goal: Here we investigated the changes in visual performance fields with external noise to determine whether the observed asymmetries are due to sensitivity or internal noise. Contrast sensitivity (CS) varies at isoeccentric locations. Specifically, CS is higher on the horizontal (East and West) than the vertical (North and South) meridian. Along the vertical meridian, CS is higher in the South than the North (e.g. Carrasco, Talgar, & Cameron, 2001). Generally, perceptual performance is a conjoint measure of the sensitivity to the signal and the amount of internal noise. Examining CS as a function of noise contrast reveals the equivalent input noise of the visual system. This value indicates the level of external noise at which internal noise ceases to dominate signal processing (Pelli & Farell, 1999).
Method: Observers performed an orientation discrimination task on Gabors of varying contrast at four isoeccentric locations (North, South, East, and West). The Gabors were embedded in Gaussian white noise of varying contrast. We measured the 75% performance threshold for each location and noise contrast and plotted threshold versus noise contrast functions for each location.
Results: Without external noise, thresholds were lowest in the East and West, higher in the South, and highest in the North. However, as noise contrast increased, thresholds increased the most at the East and West, less in the South, and least in the North. Thus, the equivalent input noise is lowest on the horizontal meridian, higher in the South, and highest in the North. At a high enough level of external noise, the thresholds for all four locations were the same. These data suggest that the differences in processing between the two meridians and within the vertical meridian are due to variations in internal noise across the visual field.
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