Twelve participants were trained to be experts at identifying a set of 'Greebles', novel objects that, like faces, all share a common spatial configuration. Tests comparing expert with novice performance revealed: (1) a surprising mix of generalizability and specificity in expert object recognition processes; and (2) that expertise is a multi-faceted phenomenon, neither adequately described by a single term nor adequately assessed by a single task. Greeble recognition by a simple neural-network model is also evaluated, and the model is found to account surprisingly well for both generalization and individuation using a single set of processes and representations.

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Research by D. L. L. A. Cooper (e.g.. Schacter cl al.. 1990. 1991) has shown that certain variables can dissociate explicit and implicit memory on recognition and object decision tests. If the same type of implicit memory representation is used in the affective preference test as in the object decision test, similar dissociations should occur for recognition and affect judgments. In 3 experiments the authors found a number of dissociations. However, unlike previous research that found object decision priming only for possible figures, a mere exposure effect was observed for possible and impossible figures. The authors conclude that the mere exposure effect is based on implicit memory, but it can be based on a different type of implicit memory representation than that used for object decision priming. D. L. Schacter and L. A. Cooper's conception of a structural description system was used to describe the findings and to provide a new interpretation of the mere exposure effect.

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Previous investigations have shown that participants are biased to respond "possible" to studied items when asked to decide whether objects could or could not exist in an object possibility test. The present study clarified and extended the concept of bias in implicit memory research in two ways. First, the authors showed that participants were biased to respond "possible" (rather than "impossible") on the object possibility test because structural processing was facilitated by prior study of possible, but not impossible, portions of objects. Second, the authors demonstrated that bias in this context was a form of, not an alternative to, implicit memory, by showing priming effects in response times when accuracy scores for studied and unstudied items were equated. The authors concluded by comparing proceduralist and memory-systems accounts of implicit memory effects and suggested that the two approaches could be seen as complementary rather than conflicting.

In an attempt to reconcile results of previous studies, several theorists have suggested that object recognition performance should range from viewpoint invariant to highly viewpoint dependent depending on how easy it is to differentiate the objects in a given recognition situation. The present study assessed recognition across depth rotations of a single general class of novel objects in three contexts that varied in difficulty. In an initial experiment, recognition in the context involving the most discriminable object differences was viewpoint invariant, but recognition in the least discriminable context and recognition in the intermediate context were equally viewpoint dependent. In a second experiment, utilizing gray-scale versions of the same stimuli, almost identical viewpoint-cost functions were obtained in all three contexts. These results suggest that differences in the geometry of stimulus objects, rather than task difficulty, lie at the heart of previously discrepant findings.

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