The use of outline shape in recognizing objects was investigated in four experiments. In Experiment 1, subjects matched a shaded image to either another shaded image or a silhouette. In Experiment 2, subjects initially named shaded images; later they named either shaded images or silhouettes. Performance in both experiments was predicted by changes in the outline shape of the stimuli. The same matching (Experiment 3) and priming (Experiment 4) paradigms were then used to investigate recognition with objects that were rotated between presentations so as to change the outline shape of the object. Recognition was predicted by changes to outline shape. These results place constraints on models of object recognition, and are most compatible with viewpoint-dependent models of recognition.

In this report we present a general introduction to object recognition. We begin with brief discussions of the terminology used in the object recognition literature and the psychophysical tasks that are used to investigate object recognition. We then discuss models of shape representation. We dispense with the idea that shape representations are like the 3-D models used in computer aided design and explore instead models of shape representation that are based on feature descriptions. As these descriptions encode only the features that are visible from a particular viewpoint, they are generally viewpoint-specific. We discuss various means of achieving viewpoint-invariant recognition using such descriptions, including reliance on diagnostic features visible from a wide range of viewpoints, storage of multiple descriptions for each object, and the use of transformation mechanisms. Finally, we discuss how differences in viewpoint dependence that are often observed for within-category and b...

The identification of human actions and body postures viewed from different viewpoints was examined in four long-term priming experiments with static pictures of a human model. In Experiments 1 and 2 participants had to name or describe the pictures, and in Experiments 3 and 4 participants had to decide whether the pictures showed a possible or impossible body pose. Reliable priming effects were obtained only when priming and primed action or pose shared the same in-depth orientation (Experiments 1 and 4) and left–right reflection (Experiments 2 and 3). Having seen the same action or pose in a different orientation did not reliably facilitate identification performance later on. Also, there was no priming for poses that are impossible to perform with a human body, not even when an identical same-view prime was used. These findings suggest that the stored representations that mediate the identification of human actions and postures are viewpoint specific. One kind of stimulus that virtually all human observers encounter numerous times in their lives is other human beings, engaged in many different actions, resulting in an even greater variety of body postures. Identifying these actions and body postures must therefore be a major task of the human visual system. This task is not straightforward, though. Depending on the orientation and position of the acting body relative to the observer, different instances of a Requests for reprints should be addressed to A. Daems, Laboratory of Experimental

Epistemic actions are physical actions people take more to simplify their internal problem-solving processes than to bring themselves closer to an external goal state. In the video game Tetris, for instance, players routinely over-rotate falling shapes, presumably to make recognition or placement decisions faster or less error-prone. Along these lines, an experimental study was performed to test the hypothesis that it is easier to recognize a two-dimensional shape if it is presented in two different orientations than if it is presented in only one. In particular, we tested whether performance on a shape-based video game task was facilitated by multiple views of a shape, and whether game performance (an indirect test of memory) differed from a direct test of memory for previously presented shapes. Results show that indeed task performance is both faster and more accurate when participants see two views of a shape than when they see one, but that more than two views do not improve performance further. In addition, multiple views lead to faster performance on the video game than on the memory test, but only in the earliest stages of training. We conclude that Tetris players may rotate falling shapes manually to see the shapes in more than one orientation, which leads to faster and more accurate placement decisions.

Epistemic actions are physical actions people take more to simplify their internal problem-solving processes than to bring themselves closer to an external goal. Consider how when playing the video game Tetris, experts routinely rotate falling twodimensional shapes more than is necessary to place the shapes. One reason for such apparently unnecessary actions is that they actually help the player make placement decisions. Such actions might facilitate placement decisions if additional previews of the shape afforded by rotating it provide information about the board, particularly when there is no direct perceptual match between the shape and the board at the time of decision. The study presented here tests the hypothesis that several distinct previews of a two-dimensional shape can improve a person’s ability to recognize and use that shape when it is not correctly oriented at the time of decision. Results show that indeed task performance and recognition are faster with two different orientations than with only one. Thus, it is possible that Tetris players rotate two-dimensional Tetris shapes manually to see them in more than one orientation, as this can lead to faster decisions.

We conducted three experiments to examine whether the anterior portion of the inferior temporal (IT) lobe is involved in the processing of visual objects in humans. In the monkey, damage to this region results in severe deficits in perception and in memory for visual objects. Our study was designed to examine both these processes in a patient (DM) with bilateral damage to the anterior portion of the inferior temporal lobe. Neuropsychological examination revealed a significant semantic impairment, and a mild deficit in the discrimination of familiar objects from nonobjects. Despite these difficulties, the results of several studies indicated that DM was able to form and retain descriptions of the structure of objects. Specifically, DM showed normal perceptual priming for familiar and novel objects on implicit memory tests, even when the objects were transformed in their size and left/right orientation. These results suggest that the anterior IT is not involved in (a) the storage of pre-...