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Biomedical subjects

U Stabell

Publications and source records attributed to U Stabell.

At least 37 records · Page 2Linked to original sources
PubMed1982

Color vision in the peripheral retina under photopic conditions.

Chromaticities of spectral colors were measured during the cone-plateau period at 17 degrees, 25 degrees, 40 degrees and 60 degrees in the nasal field of view and at 40 degrees and 70 degrees in the temporal field. The results obtained in the nasal field show a progressive contraction of the color gamut with distance from the fovea with maximum shrinkage in the middle-wave region. Color discrimination in the temporal field of view was found to be much better developed than in the nasal field. Thus, all the primary hues were clearly observable at 70 degrees temporally. The exceptionally good color discrimination obtained in the present study is explained on the assumption that only cones are effectively excited upon stimulation during the cone-plateau period.

Adaptation, Ocular↗
PubMed1982

Bezold-Brücke phenomenon of the far peripheral retina.

The Bezold-Brücke phenomenon was measured during the cone-plateau period of the long-term dark-adaptation curve at 25 degrees, 40 degrees and 60 degrees in the nasal field of view, and at 40 degrees and 70 degrees in the temporal field. In striking contrast to previous measurements of the B-B phenomenon the present results generally show that an increase of the luminance level in the middle- and long-wave regions of the spectrum produces, respectively, a trend toward green and red instead of toward yellow. The present results are explained on neural rather than on photochemical mechanisms.

Color Perception↗
PubMed1981

Absolute spectral sensitivity at different eccentricities.

Absolute spectral-threshold functions were measured during the cone-plateau period and in a dark-adapted state at 0, 6, 17, 28, 45, and 65 degrees temporally to the fovea. It was found that, when the photopic functions were brought together at 660 nm, they closely coincided in the 520-700-nm region of the spectrum, irrespective of location, suggesting that the relative spectral sensitivity and the weighted contributions of the middle-and long-wave cone photopigments remain invariant across the retina. On the other hand, the results suggest that the relative contribution of the short-wave cone mechanism increases between fovea and 17 degrees, stays essentially constant between 17 and 28 degrees, and decreases between 28 and 65 degrees. Furthermore, the results suggest that the absolute sensitivity of the middle- and long-wave cones decreases between fovea and 65 degrees, whereas the absolute sensitivity of the rods increased form fovea to 17 degrees and decreases between 17 and 65 degrees degrees. Finally, the log difference between the absolute dark-adapted cone and the rod threshold was found to increase between fovea and 45 degrees and to decrease between 45 and 65 degrees.

Color Perception↗
PubMed1981

Spectral sensitivity of the dark-adapted extrafoveal retina at photopic intensities.

By using a heterochromatic brightness-matching technique, in which the test and comparison field were presented in succession, spectral equal-brightness functions were measured in a dark-adapted state at a retinal illumination of 1000 photopic trolands at 6, 28, 45, and 65 degrees temporally to the fovea. In addition, the spectral equal-brightness functions were measured at 10, 100, 1000, and 6400 photopic trolands at 17 degrees temporally. In striking contrast with previous results, all the spectral brightness functions obtained were found to be basically scotopic in form, with peak sensitivities at about 500 nm. The difference in results between the present study and previous studies could be ascribed to the difference in method employed. Thus it was found that simultaneous, relative to successive, presentation of test and comparison fields depresses rod activity in the test field to a considerable extent. It was concluded that rods may function and influence the brightness response in extrafoveal vision at much higher intensity levels than was previously assumed.

Color Perception↗
PubMed1980

Extrafoveal spectral sensitivity during dark adaptation.

The extrafoveal spectral sensitivity function was measured during dark adaptation at different intensity levels above the cone plateau of the long-term dark-adaptation curve using both flicker and heterochromatic brightness-matching techniques. During most of the cone-plateau period, the spectral sensitivity function was found to be photopic in form at all the intensity levels employed. In the dark-adapted state, the two psychophysical techniques appeared to measure different processes. Thus, the flicker technique yielded a spectral sensitivity function which was basically scotopic in form at all the intensity levels employed while the spectral sensitivity function obtained with the brightness technique was basically photopic in form. It is suggested that, in a dark-adapted state, both rods and cones contribute to the brightness response at each wavelength over the major portion of the spectrum for a long transitional intensity range when the brightness technique is used. The flicker technique, on the other hand, appears to single out the rod activity.

Adaptation, Ocular↗
PubMed1980

Variation in density of macular pigmentation and in short-wave cone sensitivity with eccentricity.

Using both absolute threshold and flicker techniques, we measured the relative spectral sensitivity at different eccentricities during the cone-plateau period of the long-term dark-adaptation curve. With both techniques the relative spectral sensitivity tended to increase with eccentricity in the short-wave region of the spectrum. The results suggest that the relatively high short-wave sensitivity of the extrafovea obtained with the threshold technique, is due both to variation in density of macular pigmentation nd in short-wave cone sensitivity, while the relatively high short-wave sensitivity obtained with the flicker technique is due to variation in density of macular pigmentation alone. The results were used as a basis for analyzing the variation in density of macular pigmentation and in short-wave cone sensitivity with eccentricity.

Color↗
PubMed1980

Spectral sensitivity in the far peripheral retina.

Relative spectral sensitivity was measured at different intensity levels 45 degrees temporally during the cone-plateau period and in a dark-adapted state. Both heterochromatic brightness matching, flicker photometry, and threshold measurements were employed. The relative spectral sensitivity obtained during the cone-plateau period was found to coincide closely with the foveal luminosity function in the long and medium regions of the spectrum irrespective of intensity and method employed, suggesting that the relative spectral sensitivities and the weighted contributions of the long- and medium-wavelength cone photopigments do not change appreciably between fovea and 45 degrees. The relative spectral sensitivity obtained in the dark-adapted state, on the other hand, was found to be purely scotopic in form invariant to intensity and method, suggesting that it is dominated almost completely by rod activity even at intensity levels commonly labeled "photopic.

Dark Adaptation↗
PubMed1979

Bezold-brücke phenomenon of the extrafoveal retina.

With the use of an asymmetric matching technique, the Bezold-Brück phenomenon of the extrafoveal retina was measured at different eccentricities during the cone-plateau period of the long-term dark-adaptation curve and after 30 min dark adaptation. The results indicate that both the rod and the cone mechanisms contribute to the luminance-dependent hue shift of the extrafoveal retina.

Color Perception↗
PubMed1977

Metabolic rate and O2 consumption in newborns during different states of vigilance.

In 135 asymptomatic newborn infants, 1--53 days of age, body weight 1,820--4,120 g, indirect calometry was performed. According to the state of wakefulness the infants showed during the testing procedure, they were divided into four groups of vigilance (V1--V4). Metabolic rate and oxygen consumption showed similar results between groups V1, V2 and V3 (deep sleep; REM sleep; wakefulness with no muscular activity). V4 infants (with muscular activity) had a higher metabolic rate and O2 consumption. Correlation between metabolic rate and body surface area is similar in V2 and V3 but shows a steeper slope in the V1 group. It is speculated that central regulatory mechanisms may account for this difference.

Basal Metabolism↗