The Luminosity Curve as Affected by the Relation between Rod and Cone Adaptation*

104

SUMMARY1. Peripheral mechanisms that might contribute to colour vision in the cat have been investigated by recording from single units in the lateral geniculate and optic tract. Evidence is presented that the input to these cells comes from a single class of cones with a single spectral sensitivity.2. In cats with pupils dilated a background level of 10-30 cd/M2 was sufficient to saturate the rod system for all units. When the rods were saturated, the spectral sensitivity of all units peaked at 556 nm; this was true both for centre and periphery of the receptive field. The spectral sensitivity curve was slightly narrower than the Dartnall nomogram. It could not be shifted by chromatic adaptation with red, green, blue or yellow backgrounds.3. In the mesopic range (0 1-10 cd/M2), the threshold could be predicted in terms of two mechanisms, a cone mechanism with spectral sensitivity peaking at 556 nm, and a rod mechanism with spectral sensitivity at 500 nm. The mechanisms were separated and their increment threshold curves measured by testing with one colour against a background of another colour. All units had input from both rods and cones. The changeover from rods to cones occurred at the same level of adaptation in both centre and periphery of the receptive field. Threshold for the cones was between 0 04 and 0-25 cd/M2 with the pupil dilated, for a spot covering the centre of the receptive field.4. None of the results was found to vary between lateral geniculate and optic tract, with layer in the lateral geniculate, or with distance from area centralis in the visual field.5. The lack of evidence for more than one cone type suggests that colour discrimination in the cat may be a phenomenon of mesopic vision, based on differences in spectral sensitivity of the rods and a single class of cones.

Section: *Discussionmentioning

confidence: 74%

Cat colour vision: one cone process or several?

Daw¹,

Pearlman²

1969

104

“…The sensitivity for the red end of the spectrum is determined exclusively by cones, that for the blue end of the spectrum exclusively by rods. Bridgman (1953) has used this method to explain the mesopic psychophysical spectral sensitivity curves. He allows for a certain amount of (unspecified) interaction of rods and cones in the neighbourhood of the wave-lengths where the two curves intersect.…”

Section: Resultsmentioning

confidence: 99%

The spectral sensitivity of the consensual light reflex

Alpern¹,

Campbell²

1962

114

Although it is well known that light falling on the human retina will reduce the size of the pupil of each eye, it still cannot be unequivocally stated that this effect is obtained by the excitation of only cones, only rods, or both rods and cones. Since the spectral sensitivities of the photopic and scotopic eye are well established the identification of the photoreceptors activating the pupil should be readily achieved by measuring the spectral characteristics of the response of the pupil to retinal stimulation. Laurens (1923) was able to demonstrate that the curve relating pupil size to wave-length (equal energy spectrum) depended upon the adaptation state of the eye. The curve for the light-adapted eye had a minimum at 554-2 m,u, the dark-adapted curve had one at 514-3 m,u. This suggests that both rods and cones may influence the size of the pupil. Since, however, the relation between pupil size and intensity of the stimulating light is non-linear, such curves tell us nothing about the amount of energy necessary at each wave-length in the spectrum to produce a constant response. It is the information obtained from this kind of curve (an action spectrum) that is required in order to compare any non-linear physiological-response characteristic to an absorption spectrum of a visual pigment or to the well-documented spectral sensitivity curves of the visual rods and cones.

“…scotopic and modified photopic spectral sensitivity curves as the most likely relevant components). Alternatively, one might imagine with Bridgman (1953) Fig. 9, further experiments will be required to distinguish between these alternatives.…”

Section: Resultsmentioning

confidence: 99%

“…scotopic and modified photopic spectral sensitivity curves as the most likely relevant components). Alternatively, one might imagine with Bridgman (1953) that in the blue the response under these conditions is exclusively determined by rods, while in the red the response is exclusively determined by cones. The continuous smooth curve in Fig.…”

Section: The Interrupted Line Inmentioning

confidence: 99%

The electroretinogram evoked by the excitation of human foveal cones

Aiba¹,

Alpern²,

Maaseidvaag³

1967

2. The action spectrum of the response obtained in this way agrees reasonably well with the observer's psychophysical foveal luminosity curve.3. For the peripheral retina, the action spectrum is similar to that of the fovea when allowance is made for differences in screening macular pigment.4. Such responses diminish when the test stimulus is focused on to the peripheral retina and disappear when the test light is focused on the blind spot.5. Therefore, the response to the test light fixated centrally is the result of the excitation only of cones mainly, if not exclusively, in the fovea.6. When the intensity of the background is reduced by a factor of 10, the action spectrum shows evidence of the effect of excitation of rods in the blue part of the spectrum and of cones in the red. These red and blue responses add linearly when combined together, provided they are adjusted to coincide in phase.