Multiple measures of laterality in Garnett's bushbaby (Otolemur garnettii)

Abstract

Behavioral laterality, a common measure of hemispheric specialization of the brain, has been examined in multiple tasks across several species of prosimian primates; however, there is inconsistency among findings between and within species that leaves many questions about laterality unanswered. Most studies have employed few measures of laterality, most commonly handedness. This study examined multiple measures of laterality within subjects in 17 captive-born Garnett's bushbabies (Otolemur garnettii) to assess the consistency of lateralized behaviors and to examine possible influences such as age, posture, novelty, and arousal to elucidate the relations between direction and strength of laterality. We measured reaching, turning bias, scent marking, tail wrapping, leading foot, side-of-mouth preference, and hand use in prey capture. Because autonomic arousal has been invoked as a determinant of strength of lateralization, we included multiple tasks that would allow us to test this hypothesis. All subjects were significantly lateralized on simple reaching tasks (P<0.01) and tail wrapping (P<0.01). Moreover, the number of animals lateralized on turning (P<0.01), leading limb (P<0.05), mouth use (P<0.01), and prey capture (P<0.01) was greater than would be expected by chance alone. There was consistency in the strength and direction of hand biases across different postures. Tasks requiring hand use were more strongly lateralized than tasks not involving hand use (P<0.001). The data do not support the assumption that arousal (as subjectively categorized) or novelty strengthens lateralized responding. The results of this study are discussed in terms of the effects of arousal, posture, and age on lateralized behavior.