Dissociating neural mechanisms underlying visual processes

Task related contrasts are examined between two intensity dimensions (luminance and equiluminant green saturation) on "What," "Where," and "How" tasks designed to rely differentially on ventral and dorsal stream mechanisms. Differences in the way these intensity dimensions drive task-specific salience suggest that the mechanisms underlying specifically "Where" and "How" tasks utilize luminance and color information differently. Also presented will be a phenomenon observed in the minimum motion method used to obtain equiluminant lights of different hues. Some observers require a predominantly green light defining patches of a square wave (alternating with a neutral gray) be made much higher in physical luminance for it to be perceived as equiluminant to neutral gray when the patches are high (10.2 cpd) spatial frequency (SF) than when they are low SF (5.1 cpd). For other observers, the green light defining high SF patches must be made much lower in luminance for green low SF patches. These observers tend to produce opposite pattern for red lights. Those who required green high SF patches to be higher in luminance than green low SF patches, required red high SF patches to be made lower in luminance than red high SF patches and those who required green high SF patches to be lower in luminance than green low SF patches, required red high SF patches to be made higher in luminance than red high SF patches. This red/green sensitivity tradeoff will be modeled using Equisalience Analysis.