The absolute threshold for vision in the cat
Publication Type: |
Journal Article |
Year of Publication: |
1951 |
Authors: |
R. Gunter |
Publication/Journal: |
The Journal of Physiology |
Keywords: |
cat, vision |
Abstract:
In recent investigations of vision in animals the methods of electrophysiology have proved an invaluable tool for the elucidation of functions of the visual apparatus. Action potentials in optic nerve fibres, as well as electro-retinograms, have been employed to this end; so that we now have a body of accurate and objective information regarding the capacities of the animal’s peripheral visual system.
Much of this information has been obtained by taling as an index of retinal sensitivity the relative energy in different parts of the spectrum necessary to produce a constant pysiological effect, such as the height of the b-wave of the retinogram (Chaffee & Hampson, 1924), or a constant retinal potential (Graham& Riggs, 1935), or a constant number of optic nerve impulses (Graham & Hartline, 1935).
By plotting sensitivity as the reciprocal of the amount of light energy necessary to produce a threshold response (or any other constant response) against wave-length, luminosity curves for various animals under different conditions of adaptation have been obtained. These curves, which describe the sensitivity of the eye to lights of various wave-length show, in most cases, fairly good agreement with the spectral distribution of sensitivity of the human eye obtained by subjective methods under similar conditions of adaptation. It is reasonable to suggest that the luminosity curve as a psychophysical function corresponds to a reaction of the retina, which manifests itself as a measurable electrical response. This quantitative electrical response has often been assumedto be the likely physiological basis of the sensation of brightness, so that, on this assumption, a constant retinal potential can be taken as a measure of the sensitivity of the retina to lights of different wave-length. This method has been widely used as a means of investigating colour vision. From the point of view of physiology, however, we are merely dealing with the spectral distribution of sensitivity under various conditions of adaptation, while properties of colour, such as brightness and hue, are purely psychological concepts, a quantitative estimation of which can only be obtained by considering the reaction of the living animal to various spectral stimuli, and it would be of interest to compare the data obtained by this method with those obtained by means of electrophysiology.
Employing the method of behavioural discrimination, the present author has undertaken a series of investigations into the question of colour vision in the cat, an animal for which a reliable body of information has already been obtained by electro-physiological and other methods.
The experiment reported in this paper was designed as a preliminary step in this direction, and was intended to supply information as to the limits of the animal’s absolute retinal sensitivity. In this case the minimal amount of white light which the animal is capable of discriminating from darkness, under conditions of complete dark-adaptation, has been taken as an index of the absolute threshold.