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There is more than one way of making you tritanopia

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Abstract

Over a large range of stimulus conditions we can rely on the signals of our long- and middle-wave cones to sustain our visual discriminations. By comparison, there is a much more constrained range of conditions over which we obtain discriminable signals from the short-wave cones; and several stimulus parameters (e.g., luminance, duration, size, retinal locus) can be manipulated to make the normal observer behave like a tritanope. Some (following Farnsworth) have sought a single factor to account for these functional tritanopias, and indeed a factor underlying several of them may be the sparseness of shortwave cones, but it may be useful to distinguish at least four forms of functional tritanopia: (i) The complete tritanopia that arises from the absence of short-wave cones in the 20-min arc center of the foveola, (ii) The high detection threshold that results from the sparseness of short-wave cones in the rest of the retina. The absolute sensitivity of individual short-wave cones may be comparable with that of other cones, but spatial integration cannot extend the psychophysically measured sensitivity to low energies as it does for other cones, (iii) The spatial imprecision of the short-wave signals when the discriminanda are small juxtaposed fields, (iv) The saturation that can occur at a post-receptoral opponent site through which the short-wave signals pass.

© 1991 Optical Society of America

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