Biomedical subjects

David L Bimler

Publications and source records attributed to David L Bimler.

5 recordsLinked to original sources

PubMed2006

Facial-expression affective attributes and their configural correlates: components and categories.

The present study investigates the perception of facial expressions of emotion, and explores the relation between the configural properties of expressions and their subjective attribution. Stimuli were a male and a female series of morphed facial expressions, interpolated between prototypes of seven emotions (happiness, sadness, fear, anger, surprise and disgust, and neutral) from Ekman and Friesen (1976). Topographical properties of the stimuli were quantified using the Facial Expression Measurement (FACEM) scheme. Perceived dissimilarities between the emotional expressions were elicited using a sorting procedure and processed with multidimensional scaling. Four dimensions were retained in the reconstructed facial-expression space, with positive and negative expressions opposed along D1, while the other three dimensions were interpreted as affective attributes distinguishing clusters of expressions categorized as "Surprise-Fear," "Anger," and "Disgust." Significant relationships were found between these affective attributes and objective facial measures of the stimuli. The findings support a componential explanatory scheme for expression processing, wherein each component of a facial stimulus conveys an affective value separable from its context, rather than a categorical-gestalt scheme. The findings further suggest that configural information is closely involved in the decoding of affective attributes of facial expressions. Configural measures are also suggested as a common ground for dimensional as well as categorical perception of emotional faces.

Emotions↗

PubMed2005

Bezold-Brücke effect in normal trichromats and protanopes.

Luminance-dependent change in color appearance--the Bezold-Brücke effect--was investigated in protanopes and related to that in normal trichromats. Spectral lights were presented at six luminance levels covering mesopic, low, and high photopic vision-across three log steps from 0.76 to 760 Td. To judge color appearance, a variant of the color-naming method was used with four primary basic color terms and a "White" response. This modification enabled us to examine apparent saturation changes along with the Bezold-Brücke hue shift. Color-naming frequency functions were acquired across ten presentations of each stimulus. Since protanopes name colors idiosyncratically, changes in color appearance cannot be quantified directly from the color-naming functions. To circumvent the difficulty, these functions were transformed into color similarity measures for analysis with multidimensional scaling purported to reconstruct individual color spaces. In these, luminance-dependent shifts in color appearance were represented by means of geometric displacements. We found that for normal trichromats, shifts measured in this way agreed with those derived in our study directly, and with the hue shifts reported in earlier studies. For protanopes, contrary to some models of dichromatic vision, changes in color appearance are significant and indicate superimposed shifts in hue and saturation. The results obtained for normal trichromats, especially for protanopes, imply that nonlinearity in the yellow-blue opponent system is insufficient to explain the Bezold-Brücke effect, given the nature of the saturation shift and the demonstrated divergence between unique hues and invariant hues.

Adult↗

PubMed2004

Colour perception in twins: individual variation beyond common genetic inheritance.

BACKGROUND: The twin method was used to examine the genotype/phenotype relationship in colour vision, by determining concordance in colour perception within pairs of monozygotic (MZ) twins and dizygotic (DZ) twins. For MZ twins, whose photopigments are genetically identical, higher concordance in colour perception was expected; conversely, differences within each MZ pair would indicate a non-genetic contribution. METHOD: Ratings of dissimilarity between successively presented colours were elicited from four MZ and three DZ twin pairs. A non-twin sibling pair and three unrelated normal trichromats were enrolled, for comparison. Concordance for each twin (sibling) pair was estimated by Spearman correlations (rs) between data matrices and by Procrustes distances (gl) between colour spaces, reconstructed from individual data using multidimensional scaling (MDS). RESULTS: For MZ twins, rs) values (0.94-0.97) were comparable to intra-individual variability and significantly higher than those for DZ twins and siblings (0.72-0.82). Further, colour spaces for MZ co-twins were less discordant, with gl values (0.008-0.029) lower than for DZ co-twins (0.073-0.079) and siblings (0.052). Finally, concordances among all pairs of subjects were summarised by a geometrical 'subject space': the mean distance between MZ co-twins was 29 per cent of that between DZ and sibling pairs. DISCUSSION: Lower concordance rates in DZ twins and siblings can be attributed to differences in the inherited arrays of photopigment genes. The high concordance for MZ twins is in line with their shared photopigment genotype, placing an upper limit on contributions to discordance from possible individual variations in non-genetic factors. Potential photoreceptor, ocular and cognitive sources of inter-twin variation are discussed.

Adolescent↗

PubMedDate not supplied

Luminance-dependent hue shift in protanopes.

For normal trichromats, the hue of a light can change as its luminance varies. This Bezold-Brücke (B-B) hue shift is commonly attributed to nonlinearity in the blue-yellow opponent system. In the present study, we questioned whether protanopes experience analogous changes. Two protanopes (Ps) viewed spectral lights at six luminance levels across three log steps. Two normal trichromats (NTs) were tested for comparison. A variant of the color-naming method was used, with an additional "white" term. To overcome the difficulty of Ps' idiosyncratic color naming, we converted color-naming functions into individual color spaces, by way of interstimulus similarities and multidimensional scaling (MDS). The color spaces describe each stimulus in terms of spatial coordinates, so that hue shifts are measured geometrically, as displacements along specific dimensions. For the NTs, a B-B shift derived through MDS agreed well with values obtained directly by matching color-naming functions. A change in color appearance was also observed for the Ps, distinct from that in perceived brightness. This change was about twice as large as the B-B shift for NTs and combined what the latter would distinguish as hue and saturation shifts. The protanopic analogue of the B-B shift indicates that the blue-yellow nonlinearity persists in the absence of a red-green signal. In addition, at mesopic levels (< or = 38 td), the Ps' MDS solution was two dimensional at longer wavelengths, suggesting rod input. Conversely, at higher luminance levels (76 td-760 td) the MDS solution was essentially one dimensional, placing a lower limit on S-cone input at longer wavelengths.

Adult↗

PubMedDate not supplied

A whiter shade of pale, a blacker shade of dark: Parameters of spatially induced blackness.

The surface-mode property of "blackness" is induced by simultaneous contrast with an adjacent, more luminant surround. As numerous studies have shown, the degree of blackness induced within an achromatic test field is a function of the relative luminance of the adjacent chromatic inducing field, but not of its hue. But in the converse case of chromatic test fields, susceptibility to blackening has been reported to vary with wavelength. The present study investigates this possibility, that some wavelengths are more susceptible. We also questioned whether "white" and "black" sensory components function as opposites in blackness appearance. We recorded the appearance of a central monochromatic test field of constant luminance (10 cd/m2), with wavelength ranging across the visible spectrum, while a broadband white annulus was set to six luminance levels ranging across three log steps. Three color-normal observers followed a color-naming technique. All six opponent-hue names and their combinations were response options; blackness and whiteness in the test field could therefore be reported independently. Of primary interest were the achromatic responses. When represented within a multidimensional space, these revealed the "white-to-black" dimension but in addition a quality (dimension) of "desaturation." Compared against chromatic properties of the test field, the results provide evidence that blackness is a function of inducing field brightness (not luminance). This result is in accord with observations made by Shinomori et al. (1997) using a different procedure. We conclude that blackness induction occurs at a stage of visual processing subsequent to the origin of the brightness signal from a combination of opponent-process channels.

Adult↗