However, for motor functions such as hand skill or hand preference, there remains considerable debate over whether animals and, in particular, nonhuman primates exhibit hemispheric specialization ( Ettlinger, 1988 Hook-Costigan & Rogers, 1997 Hopkins, 1999a McGrew & Marchant, 1997 Warren, 1980).
On the whole, these data indicate that language is not a necessary condition for the expression of hemispheric specialization in animals, at least as it pertains to perceptual, cognitive, or emotional processing. In nonhuman primates, there is also good evidence of right hemisphere specialization in individual recognition and discrimination of species-specific facial expressions ( Hamilton & Vermeire, 1988 Vermeire & Hamilton, 1998). For example, in nonhuman primates, studies suggest a left hemisphere specialization in the processing of auditory stimuli including pure tones and species-specific vocalizations ( Dewson, 1977 Hauser & Andersson, 1994 Heffner & Heffner, 1984 Petersen, Beecher, Zoloth, Moody, & Stebbins, 1978 Pohl, 1983, 1984). Recent studies in a host of vertebrates suggest that there is evidence of left and right hemispheric specialization for some perceptual, emotional, and cognitive functions ( Bisazza, Rogers, & Vallortigara, 1998 Hopkins & Fernandez-Carriba, 2002 Rogers & Andrews, 2002 Vallortigara, Rogers, & Bisazza, 1999). Therefore, whether nonhuman animals exhibit hemispheric specialization for any abilities has been a topic of considerable historical and contemporary interest in psychology, neuroscience, and a host of other scientific disciplines ( Harris, 1993). Hemispheric specialization in humans has been linked to the evolution of a variety of complex skills including tool use, handedness, gestural communication, and language ( Boesch & Boesch, 1993 Bradshaw & Rogers, 1993 Hewes, 1973 Marzke, 1997). Although clearly an oversimplification, in humans, the left hemisphere has been reported to be dominant for speech and language processing as well as for motor skills, whereas the right hemisphere is specialized for processing visual–spatial problems as well as affective valence and emotions ( Hellige, 1993). Hemispheric specialization refers to the extent to which either the left or right hemisphere is dominant for specific motor, cognitive, perceptual, or emotional processing ( Springer & Deutsch, 1998).
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