![]() ![]() Some recent studies have clearly demonstrated evidence of population-level hand preference in some species for certain measures, but the results have not always been consistent between laboratories or between species on which comparable or identical measures have been used. There have been a number of studies on hand preference for a host of behavioral measures in various nonhuman primate species (see Fagot & Vauclair, 1991 Hopkins, 1996 MacNeilage, Studdert-Kennedy, & Lindblom, 1987 Marchant & McGrew, 1991 Ward & Hopkins, 1993). Population-level handedness refers to instances in which a significant statistical majority of the subjects within a sample exhibit preference of the same hand for a specific task. Taken together, these data suggest that the left hemisphere is dominant for the planning and execution of motor processes involved in skilled movements.įrom a comparative perspective, the most common approach in evaluating whether nonhuman primates exhibit hemispheric specialization in motor functions has been to test for population-level handedness. Moreover, the application of TMS to the premotor cortex of humans has been shown to disrupt planned motor actions, particularly in the left hemisphere ( Schluter, Rushworth, Passingham, & Mills, 1998). Third, recent neurophysiological studies have reported that motor thresholds elicited by transcranial magnetic stimulation (TMS) in the primary motor cortex of the hemisphere contralateral to the preferred hand are lower than in the ipsilateral hemisphere ( Macdonell et al., 1991 Triggs, Calvanio, & Levine, 1997). ![]() Second, individuals with lesions to the left hemisphere show greater impairment (e.g., apraxia) on tasks assessing motor skill and planning ( Harrington & Haaland, 1994 Kimura, 1993 Kimura & Archibald, 1974). First, approximately 85–90% of humans report themselves as being right-handed ( Annett, 1985 Porac & Coren, 1981), and behavioral studies indicate that the right hand typically performs better than the left on tasks assessing motor skill ( Annett, 1992, 1998 Peters, 1991). There are three bodies of data that support this view. ![]() In humans, clinical and experimental studies indicate that the left hemisphere is specialized for the control of motor skill. 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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