A fundamental problem in the study of spatial perception concerns whether and how vision might acquire information about the metric structure of surfaces in three-dimensional space from motion and from stereopsis. Theoretical analyses have indicated that stereoscopic perceptions of metric relations in depth require additional information about egocentric viewing distance; and recent experiments by James Todd and his colleagues have indicated that vision acquires only affine but not metric structure from motion-that is, spatial relations ambiguous with regard to scale in depth. The purpose of the present study was to determine whether the metric shape of planar stereoscopic forms might be perceived from congruence under planar rotation. In Experiment 1, observers discriminated between similar planar shapes (ellipses) rotating in a plane with varying slant from the frontal-parallel plane. Experimental conditions varied the presence versus absence of binocular disparities, magnification of the disparity scale, and moving versus stationary patterns. Shape discriminations were accurate in all conditions with moving patterns and were near chance in conditions with stationary patterns; neither the presence nor the magnification of binocular disparities had any reliable effect. In Experiment 2, accuracy decreased as the range of rotation decreased from 80°to 10°. In Experiment 3, small deviations from planarity of the motion produced large decrements in accuracy. In contrast with the critical role of motion in shape discrimination, motion hindered discriminations of the binocular disparity scale in Experiment 4. In general, planar motion provides an intrinsic metric scale that is independent of slant in depth and of the scale of binocular disparities. Vision is sensitive to this intrinsic optical metric.Everyday human experience and performance in perceiving constant object shapes from changing perspectives in varying contexts indicate that vision acquires information about the spatial structure of environmental objects with impressive speed, reliability, precision, and generality. Despite the familiarity and functional importance of these visual achievements, we lack a theoretical understanding of the optical information and visual mechanisms on which they are based.Indeed, the specific geometric relations that might be used by vision to perceive shape have seldom been directly evaluated by psychophysical techniques. Sperling, Landy, Dosher, and Perkins (1989) recently criticized the literature on perceiving three-dimensional (3-D) structure from motion for having failed to provide such evidence. The apparent 3-D shape constancy of perceived environmental objects, however, suggests that vision usually provides information about the metric structure of environmental This research was supported in part by NIH Grants EY05926 and P30EY08126. Experiments 1-3 were conducted by S. R. Love as part of the honors program in psychology at Vanderbilt. We are grateful to Farley Nonnan and John Kuster for their help in conducting Ex...

A time delay procedure was used to increase spontaneous verbalizations of 3 autistic children. Multiple baseline across behaviors designs were used with target responses, selected via a social validation procedure, of two spontaneous responses ("please" and "thank you") and one verbally prompted response ("you're welcome"). The results indicate gains across target behaviors for all children, with occurrence across other stimuli and settings. These gains were validated socially with 10 adults. Furthermore, increases in appropriate language had no effect on levels of inappropriate speech.

Two autistic children were treated for specific fears. A three-component participant modeling procedure was implemented within a multiple baseline design across subjects. Children were exposed gradually to fearful situations, with mothers serving as therapists and reinforcers. Dependent measures were (a) number of approach steps completed, (b) frequency of verbalizations and vocalizations of fear, and (c) overall appearance of fear. Following treatment, the children functioned effectively in previously fearful situations without verbalizations or appearance of fear. Five-month and 1-year follow-up assessments with 1 child showed maintenance of treatment effects.

A cluster analytic study was conducted to empirically derive behaviorally homogeneous subtypes of pervasive developmental disorders (PDD). Subjects were clustered based on a broad range of behavioral symptoms which characterize autism. Behavioral variables were measured using several of the standardized psychometric instruments most commonly employed in assessing autistic individuals. The cluster solution indicated the presence of four distinct groups. Validity checks generally confirmed significant between-group differences on independent measures of social, language, and stereotyped behaviors. In addition, the four-group cluster solution was compared to previously developed typological systems of PDD (i.e., subcategories based on IQ early onset, styles of social interaction, and DSM-III-R diagnosis). Results generally supported both the behavioral homogeneity of the four subgroups and also several important between-group differences. The potential utility of using cluster analyses to explore subtypes of PDD is discussed.

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