Search PubMed⌕ Search

Biomedical subjects

G H Jacobs

Publications and source records attributed to G H Jacobs.

At least 109 records · Page 6Linked to original sources
PubMed1982

Prediction of aggressive behavior in basal cell carcinoma.

In this study, a series of aggressively behaving basal cell carcinomas has been contrasted with a series of the nonaggressive type (metastasizing lesions were not considered in this study). Aggressive tumors were characteristically more likely to be ulcerative and infiltrative. They were composed of small groups of cells often displaying an irregular spiky appearance; infiltration of cells in cords, only one or two cells thick, could be seen. There was loss of peripheral palisading: the cells tended not to show differentiation. Hyalinization of the stroma was more common in the aggressive tumors. It is postulated that by utilizing these criteria, the pathologist can confidently diagnose the majority of cases and forewarn the clinician that a particular tumor is potentially aggressive. Adequate treatment and careful follow-up then become feasible.

Adult↗
PubMed1982

Color vision in the spider monkey (Ateles).

Spectral sensitivity and color vision were investigated in 2 spider monkeys (Ateles) using a forced-choice discrimination paradigm. The increment-threshold spectral sensitivity functions of both animals were very similar to those of normal human trichromats; all had three regions of peak sensitivity located at 440-460, 520-540, and 670-620 nm. However, color vision tests (neutral point, anomaloscope, and wavelength discrimination) indicated that at least two qualitatively different types of color vision exist among spider monkeys. The female tested had essentially normal trichromatic color vision (although her anomaloscope match was shifted slightly in the deutan direction) with acute wavelength discrimination. The male, however, was clearly a protanomalous trichromat. He required much more red light in a red/green mixture to match a standard yellow than did normal trichromats. This variation in color vision is discussed in the context of an analogous variation known to exist among other South American monkeys.

Animals↗
PubMed1980

Rod photoreceptors and scotopic vision in ground aquirrels.

Ground squirrel retinas contain a relatively small complement of rods (5--10% of all photoreceptors) which are thought to provide the basis for a weak scotopic visual capacity. In a previous investigation of the California ground squirrel (Spermophilus beecheyi) involving the recording of a retinal gross potential, the electroretinogram (ERG), electrophysiological evidence for a viable scotopic signal could be obtained from some, but not all of the ground squirrels examined. To further pursue the possibility that there is a structural/functional discrepancy in the relationship between rod photoreceptors and scotopic vision in the ground squirrel, several experiments involving electrophysiological, behavioral, and anatomical observations have been conducted. We found that although about one-third of the ERGs recorded from a large sample of California ground squirrels lack those characteristics which would indicate the presence of a viable scotopic signal, the retinas of all the squirrels appear to contain the same small population of rod photoreceptors. Additional experiments on the golden-mantled ground squirrel (Spermophilus lateralis), including behavioral as well as ERG measurements and anatomical observations, lead to this same conclusion.

Animals↗
PubMed1979

Visual capacities of the owl monkey (Aotus trivirgatus): temporal contrast sensitivity.

Aotus monkeys were tested in a forced-choice discrimination task to determine their ability to discriminate sinusoidally flickering lights varying in temporal frequency and luminance contrast. Under conditions of moderate light adaptation this primate is maximally sensitive to lights flickering at 10 Hz while the highest frequency they can discriminate is about 42 Hz. At very low light levels (10(-5) ft L) maximum sensitivity is for 2.2--5 Hz flicker. The highest flicker rate that could be discriminated under these conditons was about 29 Hz. In comparison to humans tested in the same situation. Aotus monkeys show relatively lower sensitivity to temporal flicker under conditions of light adaptation but relatively higher sensitivity at very low light levels.

Adaptation, Ocular↗
PubMed1979

The effects of prolonged dark exposure on visual thresholds in young and adult rats.

A comparison of electroretinogram (ERG) thresholds measured on rats reared in continuous darkness and under cyclic lighting conditions shows that by 30 days of age the dark-reared animals have achieved significantly lower thresholds than the animals reared under cyclic illumination. Ten days of continuous dark exposure produces this same increase in sensitivity in adult rats reared in cyclic lighting. These changes in sensitivity appear to reflect structural changes occurring within the rod outer segments.

Age Factors↗
PubMed1978

Spectral sensitivity and colour vision in the ground-dwelling sciurids: results from golden mantled ground squirrels and comparisons for five species.

Behavioural measurements of several indices of visual sensitivity and colour vision for the golden-mantled ground squirrel (Spermophilus lateralis) are reported. The spectral sensitivity functions for this animal show a change from having a single peak at about 520 nm to having a strongly bipartite appearance with peaks at about 540 and 460 nm as the level of light adaptation is increased from low to higher levels. Discrimination tests reveal that these squirrels have dichromatic colour vision with spectral neutral points centered at 507.5 nm. Comparisons are made of the visual capacities of five species of ground-dwelling sciurids, all of which have been tested in the same situations. These comparisons indicate that: (1) the retinas of all of these species contain a small number of functional rods in addition to a much more obvious cone population; (2) the spectral sensitivity functions of these species do not show systematic variations; (3) the cone pigments found in the retinas of these animals have sensitivity peaks at about 440 and 525 nm; (4) all of these species have dichromatic colour vision; (5) there is no evidence for systematic differences in visual sensitivity or colour vision among these five species.

Animals↗
PubMed1977

Visual sensitivity: significant within-species variations in a nonhuman primate.

Among squirrel monkeys (Saimiri sciureus) there are significant sex-related differences in visual sensitivity. As measured behaviorally in an increment-thershold task, a sample of males was found to be substantially less sensitive to long-wavelength (640-nanometer) light than a group of females tested in the same way, although the two groups showed no significant differences in sensitivity to a middle-wavelength (540-nanometer) light. The two group also differed on a test designed to measure the effects of chromatic adaptation.

Animals↗
PubMed1977

Effects of constant illumination on vision in the albino rat.

The characteristics of photically-induced blinding in the albino rat were investigated with physiological (the electroretinogram--ERG) and behavioral (luminance discrimination) techniques. These indices were obtained both before and during exposure to constant illumination (2600 lux). In trast to previous results, the findings of this study indicate that both the amplitude of the ERG and the ability to discriminate test lights decline rapidly and at approximately the same rate following the onset of constant illumination. These results, in conjunction with others already in the literature, lead to the suggestion that the degree of correspondence between behavioral and other measures of photically-induced blinding is dependent on the rate of retinal degeneration.

Albinism↗