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John Foley; Lateral Context Effects on Contrast Pattern Detection and Discrimination. Journal of Vision 2017;17(10):778. doi: 10.1167/17.10.778.
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© ARVO (1962-2015); The Authors (2016-present)
Several studies have shown that lateral patterns can affect contrast detection, discrimination, and perceived contrast. The presence of lateral patterns may increase or decrease thresholds and perceived contrast. Some of the results are inconsistent and there is no comprehensive model of these phenomena. Method: In five experiments two-alternative temporal forced choice was used to determine the detection and contrast discrimination thresholds of disk gratings and Gabor patterns in the presence of simultaneously presented context patterns, which were either lateral to or superimposed fully or partially over the target pattern. The context stimuli were disk gratings, concentric annular gratings or Gabor patterns. Spatial frequency was 4 c/d and duration was 100 msec. Thresholds were measured as a function of the type, position, size, and contrast of the context stimuli. Four to six observers performed each experiment. Results: The function relating the detection threshold to the contrast of the context pattern changes from dipper-shaped to monotonic increasing to dipper-shaped as the eccentricity of the context pattern increases. Gabor flankers have larger, but otherwise similar effects. When there is a pedestal, abutting annular gratings increase thresholds at low pedestal contrasts and decrease thresholds at high pedestal contrasts. When there is a gap, an annular grating decreases thresholds at both low and high pedestal contrasts. When mask gratings of different sizes are superimposed over the target, the threshold vs mask contrast function becomes steeper and then very shallow as the mask size increases beyond the target. Model: These diverse effects are described by an elaboration of a model of pattern context effects (Foley, 1994). The model estimates the excitatory and inhibitory effects of the context patterns. Lateral patterns increase excitation multiplicatively and increase inhibition additively. Both effects decrease with eccentricity. Excitation decreases more rapidly and then increases slightly, becoming more dominant at large eccentricities.
Meeting abstract presented at VSS 2017
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