A Purkinje shift in the spectral sensitivity of grey squirrels

Abstract

1. The light-adapted spectral sensitivity of the grey squirrel has been determined by an automated training method at a level about 6 log units above the squirrel's absolute threshold.2. The maximum sensitivity is near 555 nm, under light-adapted conditions, compared with the dark-adapted maximum near 500 nm found by a similar method.3. Neither the light-adapted nor the dark-adapted behavioural threshold agrees with electrophysiological findings using single flash techniques, but there is agreement with e.r.g. results obtained with sinusoidal stimuli.

Thresholds and noise limitations of colour vision in dim light

“…It results from the difference in the scotopic, rod-based spectral sensitivity, with a peak at 500 nm and the photopic, cone-based spectral sensitivity, which peaks at 555 nm. While other changes in colour appearance are more difficult to study in animals other than humans, the Purkinje shift has been observed in various vertebrate species, including frogs [7], cats [8], ground squirrels [9] and sharks [10], just to name a few examples. The general view was that, as in humans, such a change in spectral sensitivity-depending on light intensity and the adaptation state of the eye-was an indication of a duplex retina, with cone-based colour vision in bright light and rod-based colour-blind vision in dim light.…”

Scotopic and Photopic Visual Capacities of an Arboreal Squirrel <i>(Sciurus niger</i><i>)</i>

“…On an absolute scale the squirrels' dark-adapted thresholds were about one log unit higher than those for human observers comparably tested. Later, Silver [1966] showed that light adaptation produced a clear shift in the spectral sensitivity function, from a 500 nm peak during dark adaptation to a peak near 555 nm during light adaptation. Recently, D ip p n e r and A r m in g t o n [1971] reported evidence for visual duplicity in the American red squirrel.…”

Dark adaptation in the American red squirrel (Tamiosciurus hudsonicus).

“…An estimate of the dark-adaptation curve that tree squirrels might be expected to produce was made by Tansley (1957) on the basis of electroretinographic data from the gray squirrel. Later work on the same species suggests that the estimate cannot be accurate (Arden & Silver, 1962;Silver, 1966;Tansley, Copenhaver, & Gunkel, 1961). Dodt (1962) used an electroretinographic (ERG) method to follow the course of dark adaptation in the European red squirrel.…”