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A single experiment was designed to investigate perceptual learning and the discrimination of 3-D object shape. Ninety-six observers were presented with naturally shaped solid objects either visually, haptically, or across the modalities of vision and touch. The observers' task was to judge whether the two sequentially presented objects on any given trial possessed the same or different 3-D shapes. The results of the experiment revealed that significant perceptual learning occurred in all modality conditions, both unimodal and cross-modal. The amount of the observers' perceptual learning, as indexed by increases in hit rate and d', was similar for all of the modality conditions. The observers' hit rates were highest for the unimodal conditions and lowest in the cross-modal conditions. Lengthening the inter-stimulus interval from 3 to 15 s led to increases in hit rates and decreases in response bias. The results also revealed the existence of an asymmetry between two otherwise equivalent cross-modal conditions: in particular, the observers' perceptual sensitivity was higher for the vision-haptic condition and lower for the haptic-vision condition. In general, the results indicate that effective cross-modal shape comparisons can be made between the modalities of vision and active touch, but that complete information transfer does not occur.

Two experiments were designed to examine the effect of aging on the strength of binocular rivalry suppression. To produce rivalry, orthogonally oriented sine-wave luminance gratings were presented dichoptically. The observers were then required either to discriminate the spatial location of a probe spot presented to the dominant or suppressed eye's view or to detect the presence or absence of the probe. The observers in the younger and older age groups exhibited typical rivalry suppression for both tasks (i.e., the probe was more difficult to detect or discriminate when presented to the suppressed eye), but the magnitude of the suppression was significantly larger in the older observers. This increased suppression that accompanies aging can be explained by a reduction in the inhibition produced by the binocular matching circuitry of S. R. Lehky and R. Blake's (1991) model., ((PsycINFO Database Record (c) 2007 APA, all rights reserved).)

The ability of observers to perceive three-dimensional (3-D) distances or lengths along intrinsically curved surfaces was investigated in three experiments. Three physically curved surfaces were used: convex and/or concave hemispheres (Experiments 1 and 3) and a hyperbolic paraboloid (Experiment 2). The first two experiments employed a visual length-matching task, but in the final experiment the observers estimated the surface lengths motorically by varying the separation between their two index fingers. In general, the observers' judgments of surface length in both tasks (perceptual vs. motoric matching) were very precise but were not necessarily accurate. Large individual differences (overestimation, underestimation, etc.) in the perception of length occurred. There were also significant effects of viewing distance, type of surface, and orientation of the spatial intervals on the observers' judgments of surface length. The individual differences and failures of perceptual constancy that were obtained indicate that there is no single relationship between physical and perceived distances on 3-D surfaces that is consistent across observers.