Dynamic Object Recognition in Pigeons and Humans

Article excerpt

We investigated the role of dynamic information in human and pigeon object recognition. Both species were trained to discriminate between two objects that each had a characteristic motion, so that either cue could be used to perform the task successfully. The objects were either easy or difficult to decompose into parts. At test, the learned objects could appear in their learned motions, the reverse of the learned motions, or an entirely new motion, or a new object could appear in one of the learned motions. For humans, any change in the learned motion produced a decrement in performance for both the decomposable and the nondecomposable objects, but participants did not respond differentially to new objects that appeared in the learned motions. Pigeons showed the same pattern of responding as did humans for the decomposable objects, except that pigeons responded differentially to new objects in the learned motions. For the nondecomposable objects, pigeons used motion cues exclusively. We suggest that for some types of objects, dynamic information may be weighted differently by pigeons and humans.

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Rapid and accurate recognition of objects in the environment can be critical for survival of humans and nonhumans alike, and hence the existence of cognitive processes necessary for object recognition should be widespread throughout the animal kingdom. Nevertheless, the nature of these processes could differ across species, making object recognition an interesting ability to investigate in comparative work. The visual and cognitive processes by means of which objects are recognized by shape information alone have been the subject of intensive investigation and theorizing in humans (e.g., Biederman, 1987; BuIthoff & Edelman, 1992; Edelman, 1999; Tarr & Pinker, 1989) and recently in pigeons (e.g., Friedman, Spetch, & Ferrey, 2005; Peissig, Wasserman, Young & Biederman, 2002; Spetch & Friedman, 2003; Spetch, Friedman, & Reid, 2001; Wasserman etal., 1996). Pigeons provide an interesting comparison with humans because they are highly visual creatures, but they differ substantially from humans both in their visual experiences and in the morphology of their visual system (see Husband & Shimizu, 2001; Zeigler & Bischof, 1993), each of which might impact object recognition. For example, birds, through flight, may require a different set of processes for rapid comprehension of the 3-D world than do humans. Pigeons also have two fovea-like specialized retinal areas, each of which is similar to the human fovea. One appears to be specialized for near frontal vision and presumably facilitates detection and selection of grain. The other area appears to serve more distant monocular lateral vision, and may allow navigation, approach and avoidance of objects during flying, and monitoring of predators (see Blough, 2001). Recent studies on recognition of static objects have suggested that there are interesting similarities and differences between the cognitive processes underlying the bird's eye view of the world and those that underlie our own (reviewed by Spetch & Friedman, 2006).

More recently, researchers have begun to focus on the role that motion plays in object recognition, both in pigeons and in humans. Although motion is not the only source of visual changes in the environment, it is a prominent source of dynamic information. Some important objects are frequently viewed while they are in motion, such as an approaching predator or a fleeing prey. Such dynamic information could serve an important role in object recognition. On the one hand, dynamic information could facilitate the perception of shape information by allowing the detection and recovery of structure from motion (Wallach & O'Connell, 1953). At the same time, dynamic information could provide a characteristic motion or spatiotemporal signature of the moving object that captures the manner in which shape information changes overtime (Cavanagh, Labianca, &Thornton, 2001; Stone, 1998; Vuong & Tarr, 2006). …