Biomedical subjects

C von Campenhausen

Publications and source records attributed to C von Campenhausen.

15 recordsLinked to original sources

PubMed1998

Color and lightness constancy in different perceptual tasks.

Color and lightness constancy with respect to changing illumination was studied with three different perceptual tasks: ranking of colored papers according (1) to their lightness and (2) to their chromatic similarity in photopic, mesopic, and scotopic states of adaptation, and (3) recognition of remembered colored papers after changes of illumination in photopic vision. Constancy was found in the second task, only. Excitations of light receptors and luminance channels were computed to simulate the empirical rank orders. Results of the first task can be predicted with the hypothesis that luminance channels are activated, if lightness is asked for. Sequences arranged with respect to chromatic similarity were found independent of the illuminant spectra, even if the calculated rank orders of cone excitation were changed in the altered illumination.

Adaptation, Ocular↗

PubMed1996

[An empirical study of the factor structure of needs].

First steps are made to describe the dimensional order of such wishes, needs and motives which might be of clinical importance. A currently developed inventory was administered to a sample of 241 patients suffering from neurotic and/or psychosomatic complaints. Different scoring procedures were tried, starting with 25 scales. Finally 19 scales were used and factor analysis was applied to the data obtained. Varimax rotation of the first two factors explaining 41% of total variance revealed only the most basic aspects of some of these 19 scales, while varimax rotation of the first eight factors explains 77% of total variance. This solution identified four factors defined by more than one scale and four specific factors defined by one scale each. These two factors solutions are presented and compared and some theoretical considerations are added. A modified version of this "clinical motive inventory" with 21 scales is now ready for further investigation.

Defense Mechanisms↗

PubMed1995

100 years of Benham's top in colour science.

For 100 years Benham's top has been a popular device demonstrating pattern-induced flicker colours (PIFCs). Results of early and recent investigations on PIFCs are reported and show that the phenomenon originates in phase-sensitive lateral interactions of modulated neural activity in the retina followed by additional spatial interactions in the visual cortex behind the locus of binocular fusion. Colour matches with normal colour stimuli indicate that S/(M + L) opponent neurons are involved. Dichromats do not find matching stimuli for all PIFCs. PIFCs may become useful in medical diagnosis. The phenomenon is interpreted as a side effect of a neural mechanism providing colour constancy under normal stimulus conditions.

Color Perception↗

PubMed1992

Color induction via non-opponent lateral interactions in the human retina.

Retinal connections causing colors in Benham's top (pattern induced flicker colors, PIFCs) are investigated by psychophysical experiments. PIFCs are still seen when stimuli to different cones are demodulated selectively, indicating the involvement of non-opponent channels. PIFCs also occur on retinal areas next to those affected by modulated stimuli; further, both monochromat and dark-adapted trichromats perceive PIFCs which are achromatic. These additional findings point to horizontal cells as neuronal mediators of modulated excitation leading to PIFCs. The unspecifity of the postulated connection with respect to cone types agrees with anatomic findings of Boycott, B. B., Hopkins, J. M. and Sperling, H. G. (1987, Proceedings of the Royal Society of London, B, 229, 345-379) on horizontal cells.

Color Perception↗

PubMed1990