In terms of artificial communication systems, both language-trained chimpanzees and dolphins have been reported to exhibit a left-hemisphere asymmetry in the processing of meaningful as opposed to nonmeaningful symbols or signs ( Hopkins, Morris, & Savage-Rumbaugh, 1991 Morrel-Samuels, Herman, & Bever, 1989). These findings were interpreted as evidence of a left-hemisphere asymmetry in the processing of species-specific vocalizations. In a subsequent study, Hauser and Andersson (1994) reported a fight-sided sound localization bias in the perception of conspecific calls but not heterospecific calls (i.e., bird calls) in free-living rhesus monkeys. These results were interpreted as evidence of a right-hemisphere asymmetry in the production of facial expressions by rhesus monkeys. Using a more ethological approach, Hauser (1993) recorded the movements of the mouth and face when rhesus monkeys were vocalizing and reported that the left half of the mouth and face moved before the fight half. In Japanese macaques, Peterson, Beecher, Zoloth, Moody, and Stebbins (1978) reported a right-ear advantage in the acquisition of a vocalization discrimination task. In female mice, Ehret (1987) found that the processing of ultrasonic pup sounds were better processed by the left than the fight hemisphere. Notwithstanding, whether communicative behaviors represent a unique class of lateralized behavior similar to that observed in humans remains relatively unstudied but warrants investigation given the inherent interest in linking the evolution of communication with organizational properties of the central nervous system (see Falk, 1987 Hewes, 1973 Kimura, 1993 Passingham, 1982). In fact, the complete absence of evidence for hemispheric specialization of any form in animals led some to speculate that language and hemispheric specialization evolved de novo in humans ( Corballis, 1991 Hamilton, 1977 Warren, 1980). With the exception of data on bird song ( Nottebohm, 1977), early studies in a variety of animal species failed to report any evidence of hemispheric specialization in communicative functions. Specifically, whether animals exhibit similar forms of hemispheric specialization either in their natural communication or in the use of artificial communication systems has been a topic of interest since the earliest reports of laterality in humans ( Harris, 1993). One area of investigation in the study of hemispheric specialization has been communication. Contrary to the historical accounts ( Warren, 1980), recent evidence suggests that hemispheric specialization is not unique to humans and can be found for a variety of tasks in numerous species ( Bradshaw & Rogers, 1993 Fagot & Vauclair, 1991 Hopkins, 1996b MacNeilage, Studdert-Kennedy, & Lindblom, 1987 Ward & Hopkins, 1993).
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