Scotopic and photopic visual capacitiesof an arboreal squirrel [ sciurus niger].

Behavior measurements of visualcapacities were made on fox squirrels [Sciurus niger. Spectal sensitivity functionsmeasured in the context of an increment-threshold task reveal the presence of a Purkinjeshift in this species. Under conditions of dark adaptation, the spectral sensitivityfunction is closely fit by a nomogram photpigment having a 500 nm maximum. Under conditions of light adaptation, the spectral sensitivity function is bimodal in form with peaksat about 460 and 560 nm. Several further tests of photopic visual capacity, althoughnot all entirely consistent in outcome, reveal that[a] these animals have color vision,[b] their color vision is not a normal trichromasy and, [c] only two underlyingphotopic components [with peaks at 450 and 540nm] are unmasked by chromatic-adaptationprocedures