Abstract
Purpose: S-cone discrimination depends on the chromaticity difference between the test field and the surrounding area. The current study investigated the effect of the spatial and temporal chromatic contrast of a surround to the test field on S-cone discrimination.
Methods: The experimental paradigm isolated spatial, temporal, and spatial-and-temporal chromatic contrast effects on discrimination (Zele, Smith & Pokorny, 2006). S-cone discrimination thresholds were assessed by a four-alternative spatial forced choice procedure (Smith, Pokorny & Sun, 2000). Stimuli were either metameric to the equal energy spectrum, or varied in S-cone activation along a line of constant L/M-cone activation. A model based on primate Koniocellular pathway physiology described the data (Pokorny & Smith, 2004).
Results: Spatial and temporal contrast produced equivalent reductions in chromatic discriminability as the chromatic difference between the test and surround increased. S-cone discrimination in the absence of chromatic contrast was similar to that with spatial, temporal and spatial-and-temporal contrast.
Conclusions: S-cone discrimination was determined by either the spatial or temporal contrast component of the signal. In contrast to L/M-cone discrimination, which was best in the absence of chromatic contrast (Zele, Smith & Pokorny, 2006), S-cone discrimination did not vary with spatial or temporal contrast manipulation. This may reflect differences between the receptive field organizations of the Koniocellular and Parvocellular pathways.
Supported by National Eye Institute grant EY00901 and by an unrestricted grant to the Department of Ophthalmology and Visual Science from Research to Prevent Blindness