Journal of Comparative Psychology 1999, Vol. 113, No. 2, 149-157 Copyright 1999 by the American Psychological Association, Inc. 0735-7036/99/$3.00 Hand Preference of the Common Marmoset (Callithrix jacchus)'. Problem Solving and Responses in a Novel Setting R. Cameron and L. J. Rogers University of New England Common marmosets (Callithrix jacchus) with a right-hand preference displayed shorter latencies to enter a novel room containing novel structures and objects, touched more objects, and performed more touches and more parallax movements than marmosets with a left-hand preference. These results are consistent with specialization of the right hemisphere (left hand) for fear and negative emotional states and specialization of the left hemisphere (right hand) for approach and positive emotional states. There were no effects of age or sex on any of these behaviors. This relationship between exploration and hand preference did not occur when the marmosets were tested in the home cage with a novel problem, although significant effects of both age and dominance were found in solving the problem. When an animal enters an unfamiliar environment, both approach and withdrawal behaviors are elicited (Verbeek, Drent, & Wiepkema, 1994). Although the same individual may approach some stimuli and withdraw from others, there is some evidence showing that individuals tend to show a predominance of either approach or withdrawal behavior (Misslin & Ropartz, 1981; Verbeek et al., 1994). There is no known reason why some members of a population display approach behavior and others avoidance behavior, but it is possible that these responses to novelty are associated with differential activation of the left and right hemispheres, as suggested by Davidson (1992) and Kinsbourne (1978). In humans, the right hemisphere is considered to be specialized for processing negative affective stimuli and the left hemisphere for positive affective stimuli (Bogen, 1985). Electroencephalographic procedures have indicated that in both adults and infants, positive emotions are associated with selective activation of the left frontal lobe of the cortex, and negative emotions are associated with selective activa- tion of the right frontal lobe (Davidson, 1992). Davidson further suggested that any relationship between hemispheric dominance and emotionality may be assessed by scoring approach-avoidance behavior, on the grounds that approach behavior is a positive affective state and avoidance behavior is a negative affective state. Involvement of the right hemisphere in controlling aggres- sive and fear responses has been documented in various nonhuman primates (Bogen, 1985; Silberman & Weingart- R. Cameron and L. J. Rogers, Division of Zoology, School of Biological Sciences, University of New England, Armidale, Australia. L. J. Rogers gratefully acknowledges support from the Austra- lian Research Council (Grant AO 9330984). This research formed part of R. Cameron's requirements for an honours degree at the University of New England. Correspondence concerning this article should be addressed to L. J. Rogers, Division of Zoology, School of Biological Sciences, University of New England, Armidale, NSW, 2351, Australia. Electronic mail may be sent to lrogers@metz.une.edu.au. ner, 1986). Gelada baboons have been shown to direct aggressive responses to conspecifics that they detect in their left lateral visual field (Casperd & Dunbar, 1996); this result indicates right-hemisphere activation of this response. In rhesus monkeys, there is evidence to suggest that the right hemisphere is specialized for the production and perception of facial expressions of fear (Hauser, 1993). Marmosets show a similar bias to express fear on the left side of the face (right hemisphere) and move the right side of the mouth (left hemisphere) more than the left side when making contact (approach) calls (Hook-Costigan & Rogers, 1998b). It is also known that the left hemisphere of the Japanese macaque is specialized for the perception of species-typical vocal signals (Peterson, Beecher, Zoloth, Moody, & Stebbins, 1978). Thus it would seem that for primates, as for humans, the left and right hemispheres might be specialized for approach and withdrawal (or fear) responses respectively. Hand preference is one form of the expression of the functional differences between the hemispheres, and the consistent use of one hand may reflect hemisphere domi- nance (Hellige et al., 1994; King, 1995; Ward, Milliken, Dodson, Stafford, & Wallace, 1990). On this basis, Hopkins and Bennett (1994) hypothesized that there may be a relationship between hand preference and responses to novel stimuli. They found evidence in support of this hypothesis by testing left- and right-hand-preferring chimpanzees with novel objects. Right-hand-preferring chimpanzees displayed a shorter latency to approach novel objects and touched more of them than non-right-hand-preferring chimpanzees. Thus, approach behavior and exploration appear to be associated with greater activation of the left hemisphere and avoidance behavior with greater activation of the right hemisphere. Watson and Ward (1996) found that left-hand-preferring bushbabies (Otolemur garnettii) are more active than right- hand-preferring bushbabies in a novel setting. This result confirms the association between hand preference and responding to novelty, but it is opposite to that of Hopkins and Bennett (1994), unless the higher activity level of the 149 This document is copyrighted by the American Psychological Association or one of its allied publishers. This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.