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K H Bäuml

Publications and source records attributed to K H Bäuml.

15 recordsLinked to original sources
PubMed2001

Increments and decrements in color constancy.

The present study examines whether increment-decrement asymmetries reported in a number of recent center-surround situations occur in more complex images as well. Subjects saw the CRT simulation of a whole uniformly illuminated array of foreground surfaces presented against a large background surface and, for a number of different viewing contexts, made achromatic settings over a wide range of luminance values. Three results emerged. First, subjects' achromatic loci did not fall on a single straight line in color space but rather fell on two separate lines intersecting at some point in this space. Second, the intersection points were not identical to but dependent largely on background color and showed only small effects of foreground colors. Third, cone signals that were decremental relative to the intersection point were more responsive to illuminant changes than cone signals that were incremental, the latter additionally showing some variation with foreground colors. The results are interpreted in terms of increment-decrement asymmetries. They suggest that these asymmetries occur in more complex images as well.

Color Perception↗
PubMed2000

Effects of the beholder's age on the perception of facial attractiveness.

Children have been shown to prefer faces rated as highly attractive by adults over faces rated as quite unattractive. We investigated to what extent this agreement holds not only for the general direction of preferences but for preference strengths as well. In a choice experiment, we presented 40 nine-year-old girls and their mothers and 40 twelve-year-old girls and their mothers with pairs of women's and girls' faces and asked the subjects to pick the face that appeared prettier to them. Preference frequencies and simple attractiveness scales derived from these preference frequencies by fitting the Bradley-Terry-Luce rule (Luce, D. R. (1959). Individual choice behavior: a theoretical analysis. New York: Wiley) were compared across subject groups. For the women's faces, we found no difference in preferences between nine-year-olds, twelve-year-olds, and adults, neither in direction nor in strength. For the girls' faces, we also found no major differences in preference direction, however, we did find reliable differences in preference strengths. To a considerable part these differences were due to the fact that the children showed less pronounced preferences between face stimuli than the adults. These results suggest a role of developmental factors in the perception of facial attractiveness.

Adult↗
PubMed1999

Simultaneous color constancy: how surface color perception varies with the illuminant.

In two experiments simultaneous color constancy was measured using simulations of illuminated surfaces presented on a CRT monitor. Subjects saw two identical Mondrians side-by-side: one Mondrian rendered under a standard illuminant, the other rendered under one of several test illuminants. The matching field was adjusted under the test illuminant so that it (a) had the same hue, saturation, and brightness (appearance match) or (b) looked as if it were cut from the same piece of paper (surface match) as a test surface under the standard illuminant. Matches were set for three different surface collections. The surface matches showed a much higher level of constancy than the appearance matches. The adjustment in the surface matches was nearly complete in the L and M cone data, and deviations from perfect constancy were mainly due to failures in the adjustment of the S cone signals. Besides this difference in amount of adjustment, the appearance and surface matches showed two major similarities. First, both types of matches were well described by simple parametric models. In particular, a model based on the notion of von Kries adjustment provided a good, although not perfect, description of the data. Second, for both types of matches the illuminant adjustment was largely independent of the surface collection in the image. The two types of matches thus differed only quantitatively, there was no qualitative difference between them.

Color Perception↗
PubMed1997

Discrimination and association processes for faces and non-faces: the effect of rotation.

Most current theories of face perception claim that inversion leaves the coding of non-face stimuli largely unaffected, while causing a qualitative change in the coding of faces. Empirical support for this hypothesis mainly stems from recognition studies which typically show a larger inversion decrement for faces than for other stimuli. Several recent studies using experimental paradigms that do not contain a substantial memory component have however yielded contradicting results. This observation suggests that the disproportionate effect of inversion for faces might be related to the presence, or absence, of a memory component in the experimental task. In order to explore this hypothesis we investigated the effect of inversion within a discrimination learning paradigm, which contains a memory component comparable to that included in a recognition paradigm. We compared the effect of rotation on discrimination and association processes for faces and cars, Subjects learned to discriminate pairs of similar faces and similar cars and to associated them with neutral responses. The stimulus pairs were presented upright, inverted, and additionally in two intermediate orientations. We found that discrimination performance was generally better for faces than for cars and that associations were learned faster for faces than for cars. However, we did not find any evidence that rotation affected discrimination and association processes for faces differently than for cars. In this sense, our results provide no evidence for the hypothesis that memory processes are responsible for disproportionate effect of inversion which is found in recognition experiments.

Adult↗
PubMed1996

Color appearance of mixture gratings.

We have examined how color appearance varies with spatial pattern. Subjects set color-matches between a uniform, 2 deg matching field and bars within squarewave patterns (1,2 and 4 c/deg) or the superposition of these squarewaves. The matches were set using squarewaves and squarewave mixtures with many different colors and contrasts. The color-matches satisfied the basic properties of a linear system to within a tolerance of twice the precision of repeated matches. Matches satisfied contrast-homogeneity: the contrast of the matching field was proportional to the contrast of the squarewave pattern or the mixture of squarewave patterns. Matches also satisfied pattern-superposition: if a bar in one squarewave matched one uniform field, and a bar in a second squarewave matched a second uniform field, the superposition of the two squarewave bars matched the superposition of the uniform matching fields. Matches are predicted by a model in which the color at a location is predicted by the responses of three linear, pattern-color separable mechanisms. As the individual mechanisms are pattern-color separable, meaningful pattern and color-responsivity functions can be estimated for each of the mechanisms. The estimated color-responsivity functions, based only on asymmetric color-matches, have an opponent-colors organization.

Color Perception↗
PubMed1995

Illuminant changes under different surface collections: examining some principles of color appearance.

I report the results of a set of experiments designed to study whether the visual system's adjustments to illuminant changes vary with the surface collection in a scene. Simulations of flat matte surfaces rendered under diffuse illumination were presented on a CRT monitor. Under several surface collections subjects set asymmetric color matches between a standard surface and a test surface that were rendered under illuminants with different spectral power distributions. The three subjects' data span 28 different illuminant x surface collection conditions. Five different standard surfaces were used. Two results stand out. First, a change in surface collection did not induce a substantial change in the effect of illuminant changes on the subjects' settings. In this sense the results are consistent with the hypothesis that the visual system's adjustments to illuminant changes do not depend on the surface collection. Second, the illuminant-induced changes in the subjects' settings for a given surface collection were well approximated by a von Kries model, in which the change in the von Kries coefficients is a linear function of the illuminant change. In addition, I tested the hypothesis that the gain of the signal from each cone class is regulated by the photopigment absorptions originating entirely within that cone class. I found some clear deviations from this hypothesis, which indicates interactions among the cone classes. A first-order quantification of these interactions is provided.

Color Perception↗
PubMed1994

Color appearance: effects of illuminant changes under different surface collections.

A theory about how changes in the illuminant affect the color appearance of objects must specify how the visual system's adjustments to illuminant changes vary with the surface collection in a scene. I report an experiment designed to investigate this issue. The stimuli were CRT simulations of flat matte surfaces rendered under diffuse illumination. For all combinations of 7 daylight illuminants and 12 collections of surface reflectances the subject's achromatic locus was measured on an isoluminant plane in color space. For any surface collection the changes in the achromatic locus could be well approximated by a linear transformation of the illuminant changes. These linear transformations showed relatively small variation with the surface collection. To first approximation, these results suggest that the effect of changes in the illuminant on color appearance can be described linearly and that it can be separated from the surface collection. There was an effect of the surface collection on the achromatic locus. The data rejected the idea that a surface collection's mean reflectance function might capture this effect, ruling out models of color appearance that are based on this kind of averaging assumption.

Color Perception↗
PubMed1994

Upright versus upside-down faces: how interface attractiveness varies with orientation.

A choice experiment is reported in which all pairs and triples of faces from a set of eight moderately attractive faces were presented, both upright and upside down, to 103 subjects. In each orientation, the subjects had to select the face that appeared more (pairs) or most (triples) attractive to them. For each orientation, the preference probabilities that arose from the pair and triple comparisons could be described by the BTL rule (Luce, 1959). Thus, each face was represented by two scores, one reflecting its attractiveness in the upright orientation and the other reflecting its attractiveness in the inverted orientation. Orientation affected the preference probabilities. Qualitatively, score ratios between faces decreased from upright to inverted orientation, suggesting that the faces became less discriminable by inversion. Quantitatively, the effect of inversion could be described by a simple rule that assumes a face's two attractiveness scores to be affinely related across orientations. This result indicates that inversion affected all faces about equally. The present findings are discussed with respect to faces' first- and second-order relational properties, a distinction emphasized in current theories of face perception. They suggest that the processing of first- and second-order relational properties is impaired by inversion to roughly the same degree.

Adult↗
PubMed1993

A ratio principle for a red/green and a yellow/blue channel?

There is strong empirical evidence that, under adaptation to another achromatic color stimulus, the lightness of an achromatic color stimulus depends on the ratio of the luminances of the two stimuli. In the present study, the suitability of this ratio principle is tested for two chromatic postreceptoral opponent channels. A Hering red/green channel and a non-Hering yellow/blue channel are specified as chromatic channels. The yellow/blue channel is defined by extrapolating the plane corresponding to unique green-white linearly to the reddish part of color space, using the plane's surface as the channel's equilibria. The experiment was run on an isoluminant plane, measured individually for each observer. Moving along an observer's measured opponent axes, eight adaptation stimuli were selected for each channel and spanned the whole range of the channel's coordinates. Red/green equilibria or yellow/blue equilibria were measured as excursions along the adaptation axes. For both presumed channels, the ratios of the equilibrium coordinates of test and adaptation stimuli were essentially constant. This supports the principle's suitability. However, small asymmetries were found with respect to each channel's opponent hues. The status of the proposed yellow/blue channel is discussed, as are conditions that might have favored the present findings.

Adult↗
PubMed1992

[Discrimination learning of rotated faces: a Markov analysis of coding and association processes].

30 subjects participated in a discrimination experiment learning face-letter associations under four rotation conditions (45 degrees, 90 degrees, 135 degrees, 180 degrees). Under each condition two thirds of the faces were presented twice, upright and rotated away from the vertical; the remaining faces were presented once, upright or rotated. Learning is described by a joint Markov model: For faces that are presented twice it assumes a separate association and encoding process (two-stage-model), for faces that are presented once it assumes an association process (all-or-none-model). The Markov model fits the data for all four rotation conditions. The angle of rotation does not affect learning for faces that are presented once. For faces that are presented twice it influences both the association and the encoding process. For the angles employed, the effect of rotation can be approximated linearly. The results suggest that the encoding of a rotated face differs increasingly from an upright face as a function of these angles of rotation. This confirms analogous conclusions from mental rotation experiments.

Adult↗
PubMed1991

[Color adaptation in a yellow-blue system: proof of a simple numerical relationship].

Three axes in color space are specified: a (unique) yellow - (unique) blue axis, a (unique) green - magenta axis and brightness. Based on the two chromatic axes two linear opponent colors systems are defined: a red/green-system and a yellowish/bluish-system. A numerical relation is presented to describe color adaptation for the yellowish/bluish-system under adaptation to (unique) yellow and (unique) blue: two pairs of color stimuli are equivalent with regard to the yellowish/bluish-system - consisting of a test stimulus and an adaptation stimulus, respectively - if the ratios from the yellowish/bluish-coordinates of test stimulus and adaptation stimulus are identical. A control of brightness and the red/green-system is presupposed. For several (unique) yellow and (unique) blue adaptation stimuli it is examined how a test stimulus that appears neither yellowish nor bluish changes its location on the (unique) yellow - (unique) blue axis within color space. Three observers take part in the experiment. For each observer a plane of constant brightness and the opponent colors axes are estimated experimentally. The data show that the ratios from the yellowish/bluish coordinates of test stimulus and adaptation stimulus are essentially constant. The results are compared with analogous data for the red/green-system. The findings provide evidence for the specification of the three phenomenal axes. The specification is discussed with regard to Hering's opponent colors theory and Krauskopf's three "cardinal" axes [1982, Vision Research, 22, 1123-1131].

Adaptation, Ocular↗
PubMed1991

[A simple description of color adaptation in the red-green system].

The red/green-system is examined experimentally under adaptation to green and to magenta. The theoretical basis consists of Grassmann's laws and of a new linear opponent colors theory. Besides brightness, this opponent colors theory specifies the two chromatic axes yellow-blue and green-magenta within color space. An axiom is formulated for the description of color adaptation for the red/green-system. Two pairs of color vectors are assumed to be equivalent with respect to the red/green-system if the quotients of the respective red/green-coordinates of test vector and adaptation vector are identical. For both vectors the control of the other two opponent colors systems is presupposed. The axiom is tested for four green and four magenta adaptation vectors. Three observers take part in the experiment. For each observer an individual plane of constant brightness and his or her individual opponent colors axes are estimated experimentally. For both magenta and green adaptation the data agree well with the theoretical predictions. Thus they provide empirical support for the axiom. For the red/green-system color adaptation can be described very simply if the other two opponent colors systems are controlled.

Adaptation, Ocular↗
PubMed1989

On the relationship between the menstrual cycle and the body weight and food intake of women.

Body weight and food intake of women are analyzed over the whole menstrual cycle. Over 68-94 days body weight and food intake of eight women and three men are recorded. For food intake, a diary self-report method is used. The beginning of each woman's menstrual cycle is also recorded. Body weight and food intake are regarded as stochastic processes. The theory of time series and spectral analysis is applied. As opposed to the males, in the spectra of seven females, there is a peak at a frequency with the period of the respective females' menstrual cycles. There are no further consistent differences. This sine wave reaches its maximum two to three days before menses. The data suggest that, as a first approximation, the body weight of women during a complete menstrual cycle can be described by a simple sine wave. For food intake, the spectra show hardly any differences between females and males. However, it is shown that the same sine wave as in body weight is also contained in the food intake of seven females, reaching its maximum about four days before menses.

Adult↗