David Bimler

Categorical perception of facial expressions of emotion: Evidence from multidimensional scaling

Recent studies have shown that the perception of facial expressions of emotion fits the criteria of categorical perception (CP). The present paper tests whether a pattern of categories emerges when facial expressions are examined within the framework of multidimensional scaling. Blends of five “pure” expressions (Angry, Sad, Surprised, Happy, Neutral) were created using computerised “morphing”, providing the stimuli for four experiments. Instead of attempting to identify these stimuli, subjects described the proximities between them, using two quite different forms of data: similarity comparisons, and sorting partitions. Multidimensional scaling techniques were applied to integrate the resulting ordinal-level data into models which represent the interstimulus similarities at ratio level. All four experiments yielded strong evidence that the expressions were perceived in distinct categories. Adjacent pairs in the models were not spaced at equal intervals, but were clustered together as if drawn towards a “perceptual magnet”; within each category. We argue that spatial representations are compatible with CP effects, and indeed are a useful tool for investigating them.

School Truants and Truancy Motivation Sorted out with Multidimensional Scaling

A combination of established and novel multivariate techniques was applied to the problem of school truancy. Informants described 104 truants they were acquainted with by ranking the applicability of 73 motives and causes for absence from school. Individual rankings were analyzed in the context of a multidimensional representation of the motives, derived from sorting data provided by other informants. Each ranking was interpreted as a three-dimensional vector within this “similarity space” and as a profile of 10 weights indicating the contributions of 10 “hotspots” (broad themes summarizing the motives) located in the space. The broad spectrum of motivational profiles was subdivided using clustering techniques. Five main relatively homogeneous clusters emerged, of which two cover a previously recognized pattern of parent-condoned truancy, whereas the other three are related to recognized syndromes of adolescent delinquency. There may be considerable differences between these clusters in terms of developmental antecedents, prognosis, and most effective form of intervention.

An alternative approach for the analyses and interpretation of attachment sort items

Attachment Q‐Sort (AQS) is a tool for quantifying observations about toddler/caregiver relationships. Previous studies have applied factor analysis to the full 90 AQS item set to explore the structure underlying them. Here we explore that structure by applying multidimensional scaling (MDS) to judgements of inter‐item similarity. AQS items are arranged in the MDS solution along three easily interpretable axes: a model that is compatible with but more parsimonious than factor analysis solutions. This geometrical approach suggests ways to modify the AQS—primarily a research tool—to make it more practical for clinical applications. Sets of AQS data are represented and interpreted in the three‐dimensional model as vectors. Summaries at a finer‐grained level are obtained by finding points in the model where variability across datasets is greatest. We report re‐analyses of archival (published) data, and also data collected with streamlined procedures more suitable in the field. Although not reported here, collection and analysis can both be performed online via a website. The general methodology is not restricted to the current application of toddler attachment.

Colour‐vision tests considered as a special case of multidimensional scaling

Panel tests of colour vision such as the D15 and Farnsworth–Munsell 100-Hue tests are designed to classify people into broad categories of normal or deficient colour vision. Our interest lies in finer measurements within these categories. We apply the insights and methods of multidimensional scaling to individuals’ performances on the D15 and 100-Hue tests, by interpreting these as information about the similarities between pairs of the test stimuli (16 and 85 stimuli, respectively). The results are quantitative descriptions of individual performances on the tests. There are implications for more objective test interpretations and diagnosis of colour-vision deficiencies.

MULTIDIMENSIONAL SCALING OF HIERARCHICAL SORTING DATA APPLIED TO FACIAL EXPRESSIONS

, 38, 349–357.A new algorithm for multidimensional scaling analysis of sorting data and hierarchical-sorting data is tested by applying it to facialexpressions of emotion. We construct maps in ‘‘facial expression space’’ for two sets of still photographs: the I-FEEL series (expressionsdisplayed spontaneously by infants and young children), and a subset of the Lightfoot series (posed expressions, all from one actress). Theanalysis avoids potential artefacts by fitting a map directly to the subject’s judgments, rather than transforming the data into a matrix ofestimated dissimilarities as an intermediate step. The results for both stimulus sets display an improvement in the extent to which they agreewith existing maps. Some points emerge about the limitations of sorting data and the need for caution when interpreting MDSconfigurations derived from them.

Hue and saturation shifts from spatially induced blackness

We studied changes in the color appearance of a chromatic stimulus as it underwent simultaneous contrast with a more luminous surround. Three normal trichromats provided color-naming descriptions for a 10 cd/m2 monochromatic field while a broadband white annulus surround ranged in luminance from 0.2 cd/m2 to 200 cd/m2. Descriptions of the chromatic field included Red, Green, Blue, Yellow, White, and Black or their combinations. The naming frequencies for each color/surround were used to calculate measures of similarity among the stimuli. Multidimensional scaling analysis of these subjective similarities resulted in a four-dimensional color space with two chromatic axes, red-green and blue-yellow, and two achromatic axes, revealing separate qualities of blackness/lightness and saturation. Contrast-induced darkening of the chromatic field was found to be accompanied by shifts in both hue and saturation. Hue shifts were similar to the Bezold-Brücke shift; shifts in saturation were also quantified. A stage model is proposed to account for the relationships among blackness induction and the inherent nonlinearities in chromatic and achromatic processing.

Colour-space distortion in women who are heterozygous for colour deficiency

We examined colour perception among a group of women heterozygous for colour vision deficiency. Judgements of colour dissimilarity were collected by presenting colour stimuli in groups of three for odd-one-out decisions. The judgements were summarised as one consensus colour space for the heterozygotes and another for age-matched controls. Individual differences MDS was also applied, resulting in a single colour space which can be adjusted to fit each subjects responses individually by compressing it along its axes. Heterozygous women showed a trend towards colour-space compression in a red-green dimension, or reduced salience of that dimension compared to controls, though less extreme than found in overt colour deficiency.

Color-vision variations represented in an individual-difference vector chart

The aim was to reconstruct a uniform color space that could accommodate normal and abnormal variations in color vision. Color-dissimilarity data were collected from normal trichromats and red-green deficients, using lights varying in spectral composition and luminance. The data were analyzed with an individual-differences multidimensional scaling program and resulted in a 3D group configuration. In addition, differences in saturation required a hemispherical representation for the “color plane,” with a 4th dimension obtained when a constraint of sphericity was included in the algorithm. Subject-specific color spaces were derived from this group configuration by axial compression, preceded by a rotation of the chromatic plane. In the spaces of color deficients, compression along a red-green axis occurred, though the direction of the compression differed for protans and deutans. The extent of the compression reflected the severity of abnormality. Transformations of the subject-specific color spaces — compression extent and the angle of rotation — were portrayed in a polar-coordinate chart. The chart separates normal trichromats from the red-green deficients, distinguishes protans from deutans, and quantifies the deficiency within each class.

Escher in color space: Individual-differences multidimensional scaling of color dissimilarities collected with a gestalt formation task

The structure of color perception can be examined by collectingjudgments about color dissimilarities. In the procedure used here, stimuli are presented three at a time on a computer monitor and the spontaneous grouping of most-similar stimuli into gestalts provides the dissimilarity comparisons. Analysis with multidimensional scaling allows such judgments to be pooled from a number of observers without obscuring the variations among them. The anomalous perceptions of color-deficient observers produce comparisons that are represented well by a geometric model of compressed individual color spaces, with different forms of deficiency distinguished by different directions of compression. The geometrical model is also capable of accommodating the normal spectrum of variation, so that there is greater variation in compression parameters between tests on normal subjects than in those between repeated tests on individual subjects. The method is sufficiently sensitive and the variations sufficiently large that they are not obscured by the use of a range of monitors, even under somewhat loosely controlled conditions.

Color‐space distortions following long‐term occupational exposure to mercury vapor

Color vision was examined in subjects with long‐term occupational exposure to mercury (Hg) vapor. The color vision impairment was assessed by employing a quantitative measure of distortion of individual and group perceptual color spaces. Hg subjects (n = 18; 42.1 ± 6.5 years old; exposure time = 10.4 ± 5.0 years; time away from the exposure source = 6.8 ± 4.6 years) and controls (n = 18; 46.1 ± 8.4 years old) were examined using two arrangement tests, D‐15 and D‐15d, in the traditional way, and also in a triadic procedure. From each subject’s ‘odd‐one‐out’ choices, matrices of inter‐cap subjective dissimilarities were derived and processed by non‐metric multidimensional scaling (MDS). D‐15d results differed significantly between the Hg‐group and the control group (p < 0.05), with the impairment predominantly along the tritan axis. 2D perceptual color spaces, individual and group, were reconstructed, with the dimensions interpreted as the red‐green (RG) and the blue‐yellow (BY) systems. When color configurations from the Hg‐group were compared to those of the controls, they presented more fluctuations along both chromatic dimensions, indicating a statistically significant difference along the BY axis. In conclusion, the present findings confirm that color vision impairments persist in subjects that have received long‐term occupational exposure to Hg‐vapor although, at the time of testing, they were presenting mean urinary concentration within the normal range for non‐exposed individuals. Considering the advantages of the triadic procedure in clinical evaluation of acquired color vision deficiencies, further studies should attempt to verify and/or improve its efficacy.