To explore whether effects observed in human object recognition represent fundamental properties of visual perception that are general across species, the authors trained pigeons (Columba livia) and humans to discriminate between pictures of 3-dimensional objects that differed in shape. Novel pictures of the depth-rotated objects were then tested for recognition. Across conditions, the object pairs contained either 0, 1, 3, or 5 distinctive parts. Pigeons showed viewpoint dependence in all object-part conditions, and their performance declined systematically with degree of rotation from the nearest training view. Humans showed viewpoint invariance for novel rotations between the training views but viewpoint dependence for novel rotations outside the training views. For humans, but not pigeons, viewpoint dependence was weakest in the 1-part condition. The authors discuss the results in terms of structural and multiple-view models of object recognition.

Pigeons and humans were required to discriminate coherent from random motion in dynamic random dot displays. Coherence and velocity thresholds were determined for both species, and both thresholds were found to be substantially higher for pigeons than for humans. The results are discussed with reference to differences in motion processing in mammals and birds. It is suggested that the inferior motion sensitivity of pigeons can be attributed to poorer spatiotemporal motion integration.

Pigeons were trained to discriminate pictures of intact objects from pictures of objects in which both depth from shading and depth from perspective cues were manipulated. Depth from shading was manipulated either by scrambling or by removing three-dimensional shading cues. Depth from perspective was manipulated either by presenting pictures of objects with a two-dimensional outline (l.e., a square) or with a three-dimensional outline (Le., a cube). Transfer tests with novel images suggest that pigeons perceive and utilize both types of pictorial depth cues. The implications ofthese results for our understanding of picture perception in pigeons are discussed.Numerous studies in which the perceptual and cognitive abilities of pigeons were investigated have used pictorial displays (categorization: Edwards & Honig, 1987;Hernstein & Loveland, 1964;Wasserman, Kiedinger, & Bhatt;1988; object recognition: Kirkpatrick-Steger, Wasserman, & Biederman, 1996;Wasserman et al., 1996;White, Alsop, & Williams, 1993; and spatial relations: Spetch, Kelly, & Lechelt, 1998;Spetch & Wilkie, 1994;Wilkie, Willson, & MacDonald, 1992). Much of this research is predicated on the assumption that similar cognitive processes underlie responding to both two-dimensional (2-D) and three-dimensional (3-D) stimuli and that the third dimension is adequately represented by pictorial depth cues. However, the question of whether pictorial stimuli do in fact adequately represent 3-D objects and scenes for nonhuman animals has received comparatively little empirical investigation.Evidence from object-picture equivalence studies suggests that pigeons perceive pictures as representations of real objects. Pigeons trained to discriminate simple geometric objects transfer responding to photographs oftraining objects (Cabe, 1976;Lumsden, 1977), and pigeons trained to categorize real objects (food and junk items) transfer categorical responding to photographs of both training and novel objects (Deli us, 1992;Watanabe, 1993Watanabe, , 1997. Furthermore, birds have been shown to recognize pictures of conspecifics (Trillmich, 1976). Together, these studies suggest that, under certain conditions, nonhuman animals are capable of recognizing the equivalence between 3-D objects and their 2-D pictorial representations.Although object-picture equivalence studies are able to demonstrate transfer between objects and pictures, it is not certain to what extent these findings reflect a capacityThe research presented in this paper was also presented at the International Conference on Comparative Cognition in Melbourne, FL (March 1997). This research was supported by an operating grant from the Natural Sciences and Engineering Research Council of Canada to M.L.S. We thank D. Kelly for assistance with the research. Correspondence concerning this article should be addressed to M. L. Spetch, Department of Psychology, University of Alberta, Edmonton, AB, T6G 2E9 Canada (e-mail: mspetch@psych.ualberta.ca).to perceive three-dimensionality in 2-D displays, as compared with 2-D fe...

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