The first main objective of this study is to isolate psychophysically three post-receptoral mechanisms in human vision, luminance (Lum), red- green chromatic (RG), blue-yellow chromatic (BY), and to study some important properties of the mechanisms: 1) The interactions of the three cone types (L, M and S) in each mechanism at threshold. 2) The effect of temporal frequency on the relative phase of the cone interactions. 3) The ability of each mechanism to signal motion. Psychophysical isolation can be extremely difficult to achieve and we have developed new procedures which we believe will work--procedures which take advantage of different cone phase lags within the three mechanisms. There are some controversial questions which we then hope to answer. One is the ratio of L and M inputs in the yellow limb of the BY mechanism. Another has to do with the way in which S cones signal motion (an effect which we have clearly demonstrated); is this via the weak S cone input to the Lum mechanism? This leads to an even more basic question: are BY or RG capable of signalling motion? The putative motion sensitivity of the RG system is extremely controversial and very little threshold data (data most likely to be free of artifact) are available. We are especially interested in quantifying S cone inputs to the three mechanisms. The S cones are disproportionally vulnerable in many occular conditions (e.g. retinitis pigmentosa, macular degeneration), as well as several systemic disorders (e.g. diabetes mellitus), and so a better basic understanding of the S cone contribution to luminance and color may have future clinical applications as well. The second main objective is to understand better the facilitation by suprathreshold luminance edges of chromatic detection across the luminance boundary. A simple hypothesis for the facilitation is that it is the consequence of a reduction in spatio-temporal uncertainty. We have designed two experiments, using detection statistics, to test this hypothesis. Our previous data show that the luminance edge linearizes chromatic detection across time; additional experiments will test whether this linearity also occurs across space, so that the observer is sensitive to the linear chromatic difference across the luminance edge (like a linear, chromatic double-opponent mechanism).
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