Visual Pigments in Man

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Abstract

The importance of being able to study the visual pigments in man lies in this; that visual performance depends upon the nature, amount and state of bleaching of the pigments in the rods and cones. There are two distinct ways in which visual pigments are related to vision. The first, (a), is easy to comprehend; roughly it is that receptors can only respond to the quanta they catch, and hence the spectral sensitivity of the receptor will correspond to the spectral absorption of the pigment it contains. The second, (b), is far more difficult to comprehend though the relation can easily be stated. Roughly it is that in recovery after bleaching, the logarithm of the visual threshold is raised by a quantity proportional to the fraction of pigment still in the bleached state.