Biomedical subjects

C Redies

Publications and source records attributed to C Redies.

59 records · Page 4Linked to original sources

PubMed1984

The neon color effect in the Ehrenstein pattern. Dependence on wavelength and illuminance.

The neon color effect can be described as an illusory spread of color surrounding colored lines embedded in certain line gaps. The effect is seen in the Ehrenstein pattern if colored crosses are added to the central gaps so as to connect the inner tips of the pattern. Experiments were conducted to explore the dependence of this neon color effect on the wavelength and retinal illuminance of the inducing lines. The following results were obtained: neon color effects are strong when the wavelength of the crosses is in the short- (less than 480 nm) or long-wave part of the spectrum (greater than 620 nm) and the wavelength of the Ehrenstein pattern is in the middle-wave part (500-580 nm). Effects are weak or absent when the crosses and the pattern have similar wavelengths. The neon color effect is just detectable when the ratio between the retinal illuminances of the Ehrenstein pattern and the crosses ranges from 0.1 to 0.8. The neon color effect is maximal at illuminance ratios ranging from 0.8 to 8. The strength of the neon color effect is independent of the illuminance level of the crosses if the illuminance ratio to the Ehrenstein pattern is maintained.

Color Perception↗

PubMed1984

Colored neon flanks and line gap enhancement.

When a colored line connects two black (or differently colored) lines across a gap, colored neon flanks are seen on either side of it. These flanks extend over gap sizes of 50 min arc foveally and are not explained by Bezold-type assimilation. They may be elicited by black lines as short as 6 min arc adjoining the colored line at each end. To maximize these flanks, the black and colored lines must appear linearly continuous. Nonaligned junctions weaken the effect and an angular tilt of more than 40 dog destroys it. In this and other respects, (local) neon flanks are similar to van Tuijl's (global) neon color spreading (1975). Both phenomena have analogs in brightness perception. We propose that neon spreading is a lateral extension of neon flanks across the empty space between them, and discuss similarities of these effects with other brightness illusions (Schumann, Prandtl, Ehrenstein). For this group of illusions the term "line gap enhancement" is introduced to imply perceptual enhancement of changes in brightness and/or color along lines. Correspondences between the psychophysical properties and structural prerequisites for line gap enhancement on one hand and neuronal response properties of end-zone inhibited (hypercomplex) cortical cells on the other are discussed.

Color Perception↗

PubMed1982

The neon color effect in the Ehrenstein illusion.

Van Tuijl's neon color effect arises in the Ehrenstein figure if a colored cross is added such as to connect the black arms across the central gap. The effect consists of a circular veil of color in the illusory area and has the same hue as the inducing cross. The neon-like coloration is uniform, or when elicited by two color bipartite; it is strongest on backgrounds resembling the color of the cross. The effect cannot be attributed to chromatic aberration or eye movements. In foveal vision (and for red crosses) neon spreading is limited to gap sizes between 4 and 35 min of arc. Extrafoveally, gap sizes may be larger by a factor of two. Neon perception is enhanced by flicker and weakened if stimuli are oriented obliquely. It does not occur with dichoptic presentation. A maximum illusion requires that the Ehrenstein figure and cross are laterally and angularly aligned for good perceptual continuation. A neuronal origin by spreading and summation, together with cognitive processes, is proposed.

Afterimage↗

PubMed1981

Random-dot motion displaces Ehrenstein illusion.

When a random-dot screen is used as a background for Ehrenstein figures, brightness enhancement is replaced by a change of grain and structure. Dots in the illusory area appear less densely packed and may be perceived as concentrically organized. When the screen is moved with respect to the Ehrenstein figures, the illusory patches seem to move in the same direction and out of the inducing area while maintaining their characteristic organization. It is proposed that neurophysiological mechanisms with different persistencies are involved in producing the observed phenomenon. It is also suggested that random dots moving along the same open path are combined into a figure, whereas dots crossing the lines of the pattern remain unstructured and serve as a ground against which the displacement is seen.

Humans↗

PubMedDate not supplied

Granule cell raphes in the cerebellar cortex of chicken and mouse.

The cerebellar cortex of the chicken embryo contains parasagittal segments of Purkinje cells. At intermediate stages of development, cell-dense ribbons of migrating granule cells ("raphes") are found between the segments. The complementary pattern of granule cell raphes and Purkinje cell segments represents a basic scheme of cerebellar organization that coincides with the expression domains of various genes, such as cadherins, gene regulatory proteins, and ephrins and their receptors. We have recently found the raphe/segment pattern also in a mammalian species, the postnatal mouse. Like in the chicken, the parasagittal raphes of granule cells were observed at the boundaries of Purkinje cell segments that differentially express cadherins. The number and arrangement of the raphes in the different cerebellar lobules is roughly similar in both species. The raphe/segment pattern is thus more widely distributed in vertebrates than previously assumed.

Animals↗