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.
