'Double-blindsight' revealed through the processing of color and luminance contrast defined motion signals.
Background perturbation techniques using both static and dynamic luminance contrast and chromatic contrast noise have been employed to investigate the interaction between luminance and chromatic contrast signals. A number of experiments involving contrast detection thresholds for static stimuli, simple reaction times, and pupil color responses yield evidence for independent processing of luminance and color signals. One exception is the perception of color-defined coherent motion of randomly distributed checks when dynamic, luminance-defined, motion signals can disrupt completely the perception of coherent motion. When the moving stimulus contains color-defined, recognizable features that are spatially distinct from background noise, the perception of coherent motion is restored and becomes completely independent of dynamic luminance contrast noise. Feature-tracking mechanisms must therefore play a major part in the detection of color-defined motion. Other findings reveal the existence of a motion channel that receives exclusively achromatic inputs and a separate channel that extracts and combines luminance contrast and color-defined motion signals. Further studies carried out to investigate the interaction between luminance and chromatic signals show that color-defined, position-change thresholds are mediated by motion detection mechanisms and are, therefore, also disrupted by dynamic luminance contrast noise. In spite of the perceived uncertainty of spatial location, other experiments show that accurate, color-defined position information is preserved and available for use in other tasks. For example, accurate position information can be used to detect the vertical misalignment of color-defined checks, independently of luminance contrast noise, even when position-change thresholds are severely impaired. The analogy with 'blindsight' is obvious and irresistible. 'Blindsight' describes the ability to make accurate use of visual information in the absence of conscious visual perception. The findings that have emerged from this investigation reveal the ability of normal subjects to discard misleading, consciously perceived visual signals. The ability to override perception and to make good use of accurate visual information, in spite of misleading percepts, can best be described as 'Double-blindsight'.
Barbur
John L
JL
Applied Vision Research Centre, City University, Northampton Square, London, EC1V 0HB, UK. johnb@city.ac.uk
D001364:Awareness / Q000502:physiology*; D003118:Color Perception / Q000502:physiology*; D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D008029:Lighting; D009039:Motion Perception / Q000502:physiology*; D014785:Vision, Ocular / Q000502:physiology*