Color vision in humans depends on particular receptor cells called cones in the retina of the eye. One population of cones, known as the short-wavelength cones or S-cones is most sensitive to light in the blue region of the spectrum; others are the medium-wavelength or M-cones, and long-wavelength or L-cones, most sensitive to red. Cones contribute to two conceptual channels of information leading to visual perception. Intensity of light stimuli is signalled in the luminance channel, and color of light is signalled in the chromatic channel. Sorting out the relative contributions of the different kinds of receptors to these different channels has been an important problem. This project will examine the temporal properties of the chromatic and luminance contributions. A human subject will set flicker of a colored test light to be at just the threshold of visible flickering. The frequency or the intensity of the flicker, or the background, or a second stimulus that tends to mask or augment the flicker of the first, can all be varied. Using very intense lights, this lab already discovered that S- cones can contribute to the luminance channel. Fast responses to light intensity apparently use a brisk pathway to a luminance channel, while slower responses to color use a sluggish pathway to a chromatic channel. The current project will asses the relative prominence and the temporal properties of the two pathways at more normal light levels, and try to determine if the S-cone contribution to luminance is important at these lower levels. This work uses innovative techniques and methodology for delivering and analyzing pulsing stimuli, and results from this work will be very important to theories of color vision, to commercial engineering measurements of colored lights, and to understanding human vision in general.
