Object Recognition and Object Categorization in Animals

One of the most important attributes of cognitive activities in both human and nonhuman animals is the ability to recognize individual objects and to categorize a variety of objects that share some properties. Wild-living spider monkeys, for example, individually recognize their partners and a large number of other conspecifics quickly and accurately regardless of their highly variable spatial attitudes and also discriminate them from other species (T. Delius, personal observation). Object recognition and object categorization are both equally vital for most of the advanced animals. The retinal image of an object varies as a function of orientations, distances, lighting conditions, background scenes, and so forth at the time of viewing. Invariance operations are required for animals to identify objects despite variability of retinal stimulation. Observers may recognize the differences in orientation, location, size, and other aspects, but these differences do not obscure the identity of the objects. On the other hand, animals categorize a large number of individual objects into the same classes. There is little or no doubt that animals categorize natural objects sharing some properties, such as edible, water-offering, mateable, threatening, and so forth. The ability for animals to categorize objects enables them to learn about their environments economically with a drastic decrease in the stimulus information that they have to cope with. The processes that underlie object recognition and object categorization may well differ, but both require a common response to a variety of visual inputs. Pooling of a plurality of sensory inputs into fewer but more comprehensive signals is of great ecological relevance for animals. How and to what extent is such information pooling accomplished by animals?