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H. Sun, B.B. Lee; Polarity Reversal as a Tool for Isolating Luminance and Chromatic Contributions to a Vernier Task . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3191.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: A new technique is used to assess the role of luminance and chromatic pathways in vernier performance. Vernier thresholds are known to be elevated when a target pair has opposite contrast polarities. Psychophysical vernier thresholds were measured for pairs of gratings of various combinations of luminance and chromatic contrast polarities. Methods: The luminance (Lum) and chromatic (Chr) contrasts of the grating pair were either the same (+) or opposite (-) polarity, or zero contrast (0). Psychophysical vernier thresholds in parafovea were estimated using a staircase method. Comparison physiological data were collected from parafoveal ganglion cells of the retinae of anesthetized macaques. The spatial variability of cell responses to drifting gratings of various luminance and chromatic contrast was assessed using both Fourier analysis and a template matching technique. Results: Psychophysical vernier thresholds were grouped by luminance contrast polarity. Thresholds were low when the two gratings had the same luminance contrast polarity (+Lum/+Chr, +Lum/-Chr, +Lum/0Chr), and were elevated to a similar degree when the luminance contrast polarities were set opposite (-Lum/+Chr, -Lum/-Chr, -Lum/0Chr). Thresholds were also elevated for zero luminance contrast conditions (0Lum/+Chr, 0Lum/-Chr). In the physiological experiments, positional precision of MC cells' 1st harmonic responses deteriorated at equiluminance, but significant positional information was present in 2nd harmonic response components. Positional information in PC cells' responses was mainly dependent on the chromatic contrast. Conclusions: Psychophysical data are consistent with the luminance pathway providing critical information for vernier performance if luminance contrast is present. Spatial information at equiluminance could be derived from both MC and PC cell signals; manipulation of spatial and temporal parameters may provide information to distinguish these possibilities.
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