1. An oft-cited view, derived principally from the writings of Gordon L. Walls, is that relatively few mammalian species have a capacity for colour vision. This review has evaluated that proposition in the light of recent research on colour vision and its mechanisms in mammals. 2. To yield colour vision a retina must contain two or more spectrally discrete types of photopigment. While this is a necessary condition, it is not a sufficient one. This means, in particular, that inferences about the presence of colour vision drawn from studies of photopigments, the precursors of photopigments, or from nervous system signals must be accepted with due caution. 3. Conjoint signals from rods and cones may be exploited by mammalian nervous systems to yield behavioural discriminations consistent with the formal definition of colour vision. Many mammalian retinas are relatively cone-poor, and thus there are abundant opportunities for such rod/cone interactions. Several instances were cited in which animals having (apparently) only one type of cone photopigment succeed at colour discriminations using such a mechanism. it is suggested that the exploitation of such a mechanism may not be uncommon among mammals. 4. Based on ideas drawn from natural history, Walls (1942) proposed that the receptors and photopigments necessary to support colour vision were lost during the nocturnal phase of mammalian history and then re-acquired during the subsequent mammalian radiations. Contemporary examination of photopigment genes along with the utilization of better techniques for identifying rods and cones suggest a different view, that the earliest mammals had retinas containing some cones and two types of cone photopigment. Thus the baseline mammalian colour vision is argued to be dichromacy. 5. A consideration of the broad range of mammalian niches and activity cycles suggests that many mammals are active during photic periods that would make a colour vision capacity potentially useful. 6. A systematic survey was presented that summarized the evidence for colour vision in mammals. Indications of the presence and nature of colour vision were drawn both from direct studies of colour vision and from studies of those retinal mechanisms that are most closely associated with the possession of colour vision. Information about colour vision can be adduced for species drawn from nine mammalian orders.(ABSTRACT TRUNCATED AT 400 WORDS)

The distribution and nature of colour vision among the mammals.

The electroretinogram: Its components and their origins

Oscillatory potentials in the retina: what do they reveal.

We have examined the effects of light on circadian locomotor rhythms in retinally degenerate mice (C57BL/6J mice homozygous for the rd allele: rd/rd). The sensitivity of circadian photoreception in these mice was determined by varying the irradiance of a 15 min light pulse (515 nm) given at circadian time 16 and meauring the magnitude of the phase shift of the locomotor rhythm. Experiments were performed on animals 80 days of age. Despite the loss of visual photoreceptors in the rd/rd retina, animals showed circadian responses to light that were indistinguishable from mice with normal retinas (rd/+ and +/+). While no photoreceptor outersegments were identified in the retina of rd/rd animals (80–100 days of age), we did identify a small number of perikarya that were immunoreactive for cone opsins, and even fewer cells that contained rod opsin. Using HPLC, we demonstrated the presence and photoisomerization of the rhodopsin chromophore 11-cis retinaldehyde. The rd/rd retinas contained about 2% of 11-cis retinaldehyde found in +/+ retinas. We have yet to determine whether the opsin immunoreactive perikarya or some other unidentified cell type mediate circadian light detection in the rd/rd retina.

Circadian photoreception in the retinally degenerate mouse (rd/rd).

Sensory Mechanisms of the Retina

Anatomical, electrophysiological and pigmentary aspects of vision in the bush baby: An interpretative study

New components of the mammalian receptor potential and their relation to visual photochemistry.

Effects of hereditary degeneration of the retina on the early receptor potential and the corneo-fundal potential of the rat eye

Mode of generation of the early receptor potential

IT has been shown that, in the rabbit, retinal ganglion cells1, geniculate cells2,3 and midbrain cells4 respond most readily to special aspects of light stimulation related to movement. In the cat5–7, by contrast, these peripheral systems respond most effectively to an alteration of intensity of a stationary light spot, and have their receptive fields concentrically arranged with “on-centres and off-surrounds” (or vice versa). In the rabbit, on the other hand, the shape and organization of peripheral receptive fields are less stereotyped.

G.B. Arden

Papers

Anatomical, electrophysiological and pigmentary aspects of vision in the bush baby: An interpretative study

New components of the mammalian receptor potential and their relation to visual photochemistry.

Effects of hereditary degeneration of the retina on the early receptor potential and the corneo-fundal potential of the rat eye

Mode of generation of the early receptor potential

Rabbit Visual Cortex: Reaction of Cells to Movement and Contrast