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Biomedical subjects

R D Freeman

Publications and source records attributed to R D Freeman.

At least 145 records · Page 8Linked to original sources
PubMed1973

Visual experience without lines: effect on developing cortical neurons.

Kittens were reared in a planetarium-like visual environment that lacked straight line contours. Cortical neurons were subsequently highly sensitive to spots of light but not to straight lines, in marked contrast to those from a normal cat. If linear contour processing is an innate function it appears to be subject to substantial modification by early visual experience.

Action Potentials↗
PubMed1973

Electrophysiological evidence that abnormal early visual experience can modify the human brain.

Visual resolution in humans is nearly equal for vertically and horizontally oriented detail, but for some subjects there is a substantial difference in resolving power for these orientations. Although subjects who exhibit this difference invariably have ocular astigmatism, optical explanations of the effect can be ruled out. Direct evidence has been found for an electrophysiological correlate to the psychophysical finding. Subjects who have reduced resolution for a pattern of a particular orientation also show a decreased evoked potential response elicited by a target of the same orientation. The results are consistent with the hypothesis that a deficiency of specific features in the early visual input can alter the organization of the visual pathways.

Astigmatism↗
PubMed1972

A neural effect of partial visual deprivation in humans.

Certain human subjects have considerable sensitivity differences in the visual resolution of vertical gratings as compared to horizontal gratings. Although only subjects with pronounced ocular astigmatism exhibit this effect, the differences are of neural, rather than optical, origin. It is argued that the resolution anisotropies result from early abnormal visual input caused by astigmatism. This abnormal input permanently modifies the brain.

Astigmatism↗
PubMed1972

Oxygen permeability of the limiting layers of the cornea.

Using polarography and suitable mathematical analysis, the oxygen permeability of an individual layer of a bilayered tissue may be determined if the oxygen consumption and permeability of the other layer are known. Results obtained on rabbit cornea indicate that the permeability of the epithelium is about four times that of the endothelium.

Animals↗
PubMed1972

Oxygen consumption by the component layers of the cornea.

1. The structural integrity of the cornea is maintained by an active fluid transport system which depends on metabolism. Experiments were designed to establish the respiratory activity of each corneal layer.2. A rapid micropolarographic technique was used to determine the oxygen consumptions of the individual layers of the rabbit cornea.3. Inherent problems of the determinations have been made minimal by the use of both denuded and whole corneal tissue preparations. Four independent measures were obtained for each limiting layer (epithelium and endothelium).4. Results show that the endothelium, epithelium and stroma use 21, 40 and 39% respectively of the total oxygen consumption of the cornea. On the basis of volumes of oxygen per unit volume tissue, epithelial oxygen utilization is about ten times that of the stroma and approximately 0.2 that of the endothelium.5. The endothelium has a larger oxygen uptake than previously reported.6. The present results, in conjunction with other studies, indicate that the ratio of glycolytic to oxidative activity in the rabbit cornea is 0.87:0.13.

Animals↗
PubMed1969

Child psychiatry.

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Brain Damage, Chronic↗