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Biomedical subjects

G H Jacobs

Publications and source records attributed to G H Jacobs.

At least 127 records · Page 7Linked to original sources
PubMed1977

Brightness preference in nocturnal and diurnal South American monkeys.

In a test situation where choice was not tied to reinforcement, both squirrel monkeys (Saimiri sciureus) and owl monkeys (Aotus trivirgatus) consistently chose to view the more luminant of a pair of lights. Over a two log unit range of luminance, the degree of preference in both species for the brighter of two lights was found to depend on their difference in luminance and not on their actual luminances.

Animals↗
PubMed1976

Scotopic and photopic vision in the California ground squirrel: physiological and anatomical evidence.

The California ground squirrel is a highly diurnal species previously thought to have an all-cone retina. This issue was re-examined in physiological and anatomical experiments. The electroretinogram (ERG) was used to measure the spectral sensitivity of the eye under different conditions of adaptation. The occurrence of a Purkinje shift could be demonstrated, although there was some indication that not all members of this species show such a shift. Spectral sensitivity of the dark-adapted eye of this squirrel is close to that predicted by a typical mammalian rhodopsin. Light adaptation produces a shift in spectral sensitivity to a peak location of about 525 nm. It was shown that two mechanisms having different spectral sensitivities contribute to the photopically recorded ERG. The degree to which these two mechanisms contribute to the ERG was found to be strikingly different from the degree to which the two contribute to visual behavior. Our anatomical results indicate that the retina of the California ground squirrel has two structurally distinct photoreceptors which, on the basis of various criteria, can be classified as cone and rod-like. The rod-like receptors comprise about 6-7% of the total. The two photoreceptor types differ in placement of their inner segments, size of their outer segments, outer segment ultrastructure, and terminal structure and organization.

Adaptation, Ocular↗
PubMed1976

Color vision.

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Animals↗
PubMed1975

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

Animals↗