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C M de Weert

Publications and source records attributed to C M de Weert.

15 recordsLinked to original sources
PubMed1992

Binocular measurements of chromatic adaptation.

In this paper we present asymmetric matching data that were obtained with a binocular presentation method. Our main motivation was the question whether chromatic adaptation, one of the important mechanisms that contribute to colour constancy, has evolved towards a better performance in the range of colours that are present in the natural image. For the eye adapted to a bluish illuminant for example the presence of an object with a deep yellow colour is very unlikely. So, it was expected that the colour difference between adapting light and target has an influence on the extent of chromatic adaptation. It was found that the colour shift in the observers' matches that can be attributed to chromatic adaptation indeed has a maximum. The location of the maximum, however, was unexpected, i.e. colour differences between target and adapting light that lie around 0.05 u'v'-chromaticity units. Additionally, several models for chromatic adaptation were fitted to our data. It was found that, except for the simple von Kries model, Retinex Theory and difference contrast, a number of models gave good predictions for the L-wave and M-wave fundamental systems, but that predictions for the S-wave system were less accurate.

Adaptation, Ocular↗
PubMed1991

Surface reflectances and human color constancy: comment on Dannemiller (1989)

Dannemiller's (1989) computational approach to color constancy is discussed in relation to human color constancy. A reflectance channel that requires a priori information is shown to be less plausible for the human visual system than Dannemiller argued. The resemblance of Dannemiller's hypothetical visual system to the human visual system is misleading because it implies that surface reflectance is the illuminant-invariant object color descriptor that the human visual system uses to achieve color constancy. However, an alternative type of descriptor is available that is not used to recover reflectance spectra. It has the advantage of allowing an interpretation that is preferable from a human perceptual point of view.

Attention↗
PubMed1991

Large color differences and selective attention.

Similarity data for large color differences, obtained with triadic comparisons, are presented. Approximately 63,000 judgments are collected. We have compared the performance of the CIELUV, the CIELAB, and the Optical Society of America's [symbol; see text] jg color spaces, using three different color sets and two instructions. For color sets containing large color differences in the isoluminant plane, the [symbol; see text] jg color space outperforms the CIELUV and CIELAB spaces. We also investigated the effects of selective attention and conclude that, for judgments of large color differences, selective attention leads to significant changes in the relative contribution of the brightness dimension on the one hand and the hue and saturation dimensions on the other hand.

Adult↗
PubMed1991

Naming versus matching in color constancy.

In this paper, a replication of the color-constancy study of Arend and Reeves (1986) is reported, and an alternative method is presented that can be used for the study of higher order aspects of color constancy, such as memory, familiarity, and perceptual organization. Besides a simultaneous presentation of standard and test illuminants, we also carried out an experiment in which the illuminants were presented successively. The results were similar to Arend and Reeves's; however, in the object-matching condition of the successive experiment, we found an overestimation, instead of an underestimation, of the illuminant component. Because the results of matching experiments are difficult to interpret, mainly due to their sensitivity to instruction effects, we introduced another type of color-constancy task. In this task, subjects simply named the color of a simulated patch. It was found that, by applying such a task, a reliable measure of the degree of identification of object color can be obtained.

Attention↗
PubMed1990

Transparent layer constancy.

Perceived transparency was studied as a constancy problem. In the episcotister (E-) model of scission, luminances are partitioned into layer and background components; four luminances determine values of two layer parameters that specify constancy of a transparent layer on different backgrounds. The E-model was tested in an experiment in which 12 Ss matched 24 pairs of four-luminance patterns by adjusting two luminances of the comparison pattern. Both the standard and the comparison were perceived as a transparent layer on a checkerboard. The E-model predicts matches when layer values are identical in the two patterns. One parameter was constant, constraining the adjustment along the second dimension. Obtained values corresponded well with E-predictions. Alternative models based on local luminance or average contrast ratios accounted for less variability. Results indicate that transparency models should utilize luminance, not reflectance, as the independent variable.

Adult↗
PubMed1988

Compound binocular rivalry.

Binocular rivalry was examined with random dot patterns consisting of three colours: red, green and grey. The microstructure of the patterns was defined by the individual dots, and the correspondence between the microstructures in the two eyes was manipulated. The macrostructures were defined by the distributions of red, green and grey dots over the displays, so that they consisted of orthogonally striped patterns. The degree of correspondence between the microstructures was varied in Expt 1, together with the spatial frequency of the microstructure. Rivalry periods of the macrostructures were briefer when the microstructures were in correspondence, In Expt 2 the spatial frequencies of the macrostructures were varied. The lower spatial frequency predominated for longer than the higher. The results are discussed in terms of independent pathways for corresponding and rivalry stimulation. In addition a stimulus pairing that produces clear dichoptic colour mixtures is presented.

Dominance, Cerebral↗
PubMed1986

Aftereffects in binocular rivalry.

Five experiments are reported in which the aftereffect paradigm was applied to binocular rivalry. In the first three experiments rivalry was between a vertical grating presented to the left eye and a horizontal grating presented to the right eye. In the fourth experiment the rivalry stimuli consisted of a rotating sectored disc presented to the left eye and a static concentric circular pattern presented to the right. In experiment 5 rivalry was between static radiating and circular patterns. The predominance durations were systematically influenced by direct (same eye) and indirect (interocular) adaptation in a manner similar to that seen for spatial aftereffects. Binocular adaptation produced an aftereffect that was significantly smaller than the direct aftereffect, but not significantly different from the indirect one. A model is developed to account for the results; it involves two levels of binocular interaction in addition to monocular channels. It is suggested that the site of spatial aftereffects is the same as that for binocular rivalry, rather than sequentially prior.

Adaptation, Ocular↗
PubMed1986

Binocular rivalry with rotary and radial motions.

Binocular rivalry between a radially sectored and a concentrically circular pattern was investigated in three experiments. Motion of the circular pattern was either cyclical expansion and contraction with corresponding changes in spatial frequency (experiment 1), or outward motion with a constant linear velocity (experiment 2). When both patterns were static the circular pattern was visible for longer than the radial one. Motion of either pattern alone resulted in an increase in the predominance duration and the mean period for which the pattern was visible. This is at variance with Levelt's model of rivalry. In the third experiment, rivalry was between a static circular pattern and a radial pattern that could be rotated at different angular velocities. Again it was found that an increase in stimulus strength, as measured by predominance, led to an increase in the mean periods of visibility of the rotating pattern.

Functional Laterality↗
PubMed1986

Spectral sensitivity functions derived from brightness matching: implication of intensity invariance for color-vision models.

It is demonstrated that brightness sensitivity functions are self-similar; i.e., unique up to multiplication by a positive constant. This invariance leads to a structural restriction for sensitivity models that are formulated in terms of action spectra of cone systems. The heuristic value of this restriction is demonstrated through simulations on various kinds of data on direct brightness matching and brightness magnitude estimation on the basis of a new model for brightness sensitivity that accounts for both superadditivity and subadditivity.

Color Perception↗
PubMed1979

Sensory conditions for the occurrence of the neon spreading illusion.

The neon effect, i.e. an illusion of light projected onto a homogeneous lattice, may occur in line patterns made up of elements of different color or brightness. Particular luminance relations between the different line elements in the patterns and between these line elements and their background appear to be critical for the occurrence of the effect.

Color Perception↗