In 2 experiments exploring memory for unfamiliar 3-dimensional objects, Ss studied drawings under conditions that encouraged encoding of global object structure. Implicit memory for objects was assessed by a judgment of structural possibility; explicit memory was assessed by recognition. The principal manipulation was the relationship between the sizes or the left-right parities of the studied and tested objects. Priming was observed on the possible-impossible object decision task despite transformations of size or reflection. Recognition, by contrast, was significantly impaired by the transformations. These results suggest that a structural description system constructs representations of objects invariant over size and reflection, whereas a separable episodic system encodes these transformations as properties of an object's distinctive representation in memory.

In three experiments we tried to mask the motions of human gait. We represented human walkers as a set of 11 computer-generated elements on a display monitor, moving as a nested hierarchy of motions that mimicked the motions of the head and major joints. The walker was seen in sagittal view, facing either right or left.and walking as if on a treadmill. On the walker was superimposed a simultaneous mask composed of elements with the same brightness, shape, and subtense as those of the walker. We varied the mask parameters-particularly the number of elements and style of motion-to discern what masks best camouflaged the walker's direction. In general, many kinds of masks impeded viewer performance at durations of 200 msec, but only relatively complex masks continued to impede performance to 400 m.sec and beyond. Four results stand out concerning the concurrent perceptual organization of target and mask. First, if the mask is easily divided into groups by its motion parameters, viewer performance with respect to the stimulus is generally impeded by increasing the number of groups in the mask. Second, the most successful masks are those composed of scrambled parts of walkers. Third, given a sufficient number of scrambled-walker elements, viewer performance does not improve above chance even at 800 m.sec. And fourth, this lack of improvement appears to be confined to scrambledwalker masks that share the particular gait parameters of the walker target.Those who study the perception of certain types of events often use the term biological motion for patterns of movement generated by living forms. By far the most frequently studied biological motion is human gait (e.g

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When comparing psychological models a researcher should assess their relative selectivity, scope, and simplicity. The third of these considerations can be measured by the models' parameter counts or equation length, the second by their ability to fit random data, and the first by their differential ability to fit patterned data over random data. These conclusions are based on exploration of integration models reflecting depth judgments. Replication of Massaro's (1988a) results revealed an additive model , and Massaro's fuzzy-logical model of perception (FLMP) fit data equally well, but further exploration showed that the FLMP fit random data better. The FLMP's successes may reflect not its sensitivity in capturing psychological process but its scope in fitting any data and its complexity as measured by equation length.Good scientific theories are usually thought to have several properties: They are accurate, simple, broad in scope, internally consistent, and have the ability to generate new research (Kuhn, 1977). When models can be used to instantiate theories, they might reflect these same properties. For our purposes the two key concepts in this set are simplicity and scope. Simplicity can be measured in several ways. We measure it in two: by the number of parameters in a model and, in a way not customary to experimental psychology, by the length of the equation that instantiates a model. Scope can also be measured in various ways, but here we consider how theory or model accounts for all possible data functions, where those functions are generated by a reasonably large sample of random data sets. Under this construal, broad scope is a mixed blessing. A model with greater scope than another may fit more data functions of interest to the researcher, but simultaneously it may also fit more functions of no interest. Thus, we propose a new criterion for testing and comparing models: selectivity. We define selectivity as the relative ability of a This research was supported by National Science Foundation Grant BNS-8818971 to James E. Cutting. Results without modeling or simulations were reported briefly at the 28th annual meeting of the Psychonomic Society, Seattle, Washington, November 1987.We thank Dominic W. Massaro for helping us understand and implement the fuzzy-logical model of perception; Michael S. Landy and Mark J. Young for insights into implementing other models; James L. McClelland for a general discussion about modeling; William Epstein, James A. Ferwerda, and Mary M. Hayhoe for random discussions related to the topics presented here; Carol L. Krumhansl, Michael S. Landy, Geoffrey R. Loftus, Dominic W. Massaro, and an anonymous reviewer for comments on previous versions of this article; and Nan E. Karwan for sustained interest in and discussions about the project.Correspondence concerning this article should be addressed to James E. Cutting, Department of Psychology, Uris Hall, Cornell University, Ithaca, New York 14853-7601. model to fit data functions of interest with its ability to fit random da...

Projection of a 3D scene onto the 2D retina necessarily entails a loss of information, yet perceivers experience a world populated with volumetric objects. Using simultaneous behavioral and neural (fMRI) measures, we identify neural bases of volume perception. Neural activity in the lateral occipital cortex increased with presentation of 3D volumes relative to presentation of 2D shapes. Neural activity also modulated with perceived volume, independent of image information. When behavioral responses indicated that observers saw ambiguous images as 3D volumes, neural response increased; when behavioral data revealed a 2D interpretation, neural response waned. Crucially, the physical stimulus was identical under both interpretations; only the percept of volume can account for the increased neural activity.