Two segmentation mechanisms with differential sensitivity for colour and luminance contrast

In a texture-segregation paradigm, subjects were asked to detect figures whose elements were segregated from background either because of temporal offset or because of differing orientations. Texture elements were either isoluminant or had high or low luminance contrast. At high luminance contrast, figures could be segregated both on the basis of orientation and temporal cues whereby temporal offsets as short as 10 msec supported detection. At isoluminance, orientation defined figures were as readily distinguishable as in the high contrast condition but temporally defined figures were perceived only for offset intervals > 50 msec. With low luminance contrast, performance for orientation defined figures was impaired relative to the high contrast condition, but for temporally defined figures, it was superior to the isoluminant condition; detection was possible for offset intervals as short as 22 msec. These results suggest that the temporal and orientation cues which support scene segmentation are transmitted by both the luminance and colour sensitive pathways. However, if temporal offsets are < 50 msec, segmentation of temporally defined figures is supported only by the luminance sensitive system.