Abstract
Two specific questions relating to colour and motion processing were addressed: 1) whether colour information is carried by a system that is sensitive to both colour and luminance information, i.e. a double-duty system, and/or a system that is sensitive purely to colour information; and 2) whether colour can be used as a segmentation cue in the pooling of motion signals. The nature of the colour input was determined by using a global dot-motion stimulus (for which performance cannot be mediated by attention-based tracking) in which the signal dots changed their luminance polarity as they moved, but maintained their colour information. The effect of luminance contrast, speed and eccentricity were investigated. A purely colour-sensitive system would be able to use the consistent colour signal, regardless of the contrast of the inconsistent luminance-signal. It was found that observers could extract motion only at both low luminance-contrast and low speeds (<12°/s). No evidence for a purely colour system was obtained, even at very low speeds and for foveally presented stimuli. The extent to which colour can be used as a segmentation cue was assessed by determining whether noise dots of one colour and luminance combination affected the extraction of a global-motion signal from noise dots of a different colour and luminance combination. It was found that colour could not be used as a segmentation cue for standard global-motion processing (consistent with earlier results), however it could be when a stimulus was used that tapped the form-specific global-motion system (VisRes, 2010, 429–438). These finding indicate: a double-duty motion system exists, both in the fovea and parafoveal region; this system is only sensitive to low speeds; a purely colour-sensitive system does not exist, and colour cannot be used as a segmentation cue in standard motion-pooling but it can in form-specific processing.