This article examines individual and group manual lateralization in nonhuman primates as a function of task's demands. It is suggested to distinguish low- from high-level manual activities with respect to the novelty variable and to the spatiotemporal scale of the movements. This review shows that low-level tasks lead to (a) symmetrical distributions of hand biases for the group and (b) manual preferences that are not indicative of the specialization of the contralateral hemisphere. In contrast, behaviors expressed in high-level tasks (a) show asymmetrical distribution of hand biases for the group and (b) seem to be related to a specialization of the contralateral hemisphere. Two types of lateralization, handedness and manual specialization, correspond to the 2 levels of tasks that are distinguished.

This study examined hand preference in baboons in a sample of 94 subjects for a unimanual task and in a sample of 104 subjects for a bimanual task. For the unimanual task, handedness was assessed by observing simple reaching for grains. For the bimanual task, tubes lined with peanut butter inside were presented to the baboons. The hand and the finger used to remove peanut butter were recorded. Population-level right-handedness was found for the bimanual but not the unimanual task. In addition, test-retest correlations showed consistency in hand use across time for the coordinated bimanual task but not the simple reaching task. No significant effects of age and sex on the direction and strength of hand preferences were found for either task. These are the first evidences of population-level handedness in baboons and the results are discussed in the context of evolutionary theories of cerebral dominance.

Three experimental designs were implemented in day nurseries in order to elicit imperative, declarative expressive, and declarative informative pointing gestures (Tomasello, Carpenter, & Liszkowski, 2007) among a population of 48 toddlers aged 15-30 months. Several features were recorded for each situation, including gesture form, gaze direction, and vocalizations. A unimanual reaching task was also administered, in order to compare laterality patterns for each type of gesture. Main results revealed that imperative gestures were associated with whole-hand pointing, whereas declarative gestures were more frequently characterized by an extended index finger. Moreover, declarative gestures were more frequently accompanied by vocalizations than imperative gestures were. Finally, different degrees of manual preference were observed, especially for informative pointing gestures, which tended to be more right-handed than reaching actions. Results of the study are discussed in relation to the nature and development of each kind of pointing gesture.

Rhesus monkeys (Macaca mulata) were subjected to a place finding task in a rectangular room perfectly homogeneous and without distinctive featural information. Results of Experiment 1 show that monkeys rely on the large-scale geometry of the room to retrieve a food reward. Experiments 2 and 3 indicate that subjects use also nongeometric information (colored wall) to reorient. Data of Experiments 4 and 5 suggest that monkeys do not use small angular cues but that they are sensitive to the size of the cues (Experiments 6, 7, and 8). Our findings strengthen the idea that a mechanism based on the geometry of the environment is at work in several mammalian species. In addition, the present data offer new perspectives on spatial cognition in animals that are phylogenetically close to humans. Specifically, the joint use of both geometric and landmark-based cues by rhesus monkeys tends to demonstrate that spatial processing became more flexible with evolution.

Within the evolutionary framework about the origin of human handedness and hemispheric specialization for language, the question of expression of population-level manual biases in nonhuman primates and their potential continuities with humans remains controversial. Nevertheless, there is a growing body of evidence showing consistent population-level handedness particularly for complex manual behaviors in both monkeys and apes. In the present article, within a large comparative approach among primates, we will review our contribution to the field and the handedness literature related to two particular sophisticated manual behaviors regarding their potential and specific implications for the origins of hemispheric specialization in humans: bimanual coordinated actions and gestural communication. Whereas bimanual coordinated actions seem to elicit predominance of left-handedness in arboreal primates and of right-handedness in terrestrial primates, all handedness studies that have investigated gestural communication in several primate species have reported stronger degree of population-level right-handedness compared to noncommunicative actions. Communicative gestures and bimanual actions seem to affect differently manual asymmetries in both human and nonhuman primates and to be related to different lateralized brain substrates. We will discuss (1) how the data of hand preferences for bimanual coordinated actions highlight the role of ecological factors in the evolution of handedness and provide additional support the postural origin theory of handedness proposed by MacNeilage [MacNeilage [2007]. Present status of the postural origins theory. In W. D. Hopkins (Ed.), The evolution of hemispheric specialization in primates (pp. 59-91). London: Elsevier/Academic Press] and (2) the hypothesis that the emergence of gestural communication might have affected lateralization in our ancestor and may constitute the precursors of the hemispheric specialization for language.

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The aim of this study was to measure the pattern of hand preferences for pointing gestures as a function of object-manipulation handedness in 123 infants and toddlers (10-40 months). The results showed that not only right-handers but also left-handers and ambidextrous participants tended to use their right hand for pointing. There was a significant correlation between manual preferences and pointing lateralization. Further analyses showed that the correlation between these two indexes was at its strongest during two key phases of language development (i.e. vocabulary spurt and syntax improvement) and weakened to become nonsignificant in the interim. These findings support the view that humans have a specialized area for communicative gestures and language in the left cerebral hemisphere that may be independent of the system controlling the purely motor functions of hand use.

a b s t r a c tThis study investigated the development of hand preference for bimanual manipulative activities and pointing gestures in toddlers observed longitudinally over a 5-month period, in relation to language acquisition. The lexical spurt was found to be accompanied by an increase in the right-sided bias for pointing but not for manipulation. Moreover, results revealed a significant correlation between hand preference for imperative pointing gestures and manipulative activities in children who did not experience the lexical spurt during the observational period. By contrast, measures of handedness for declarative pointing were never correlated with those of handedness for manipulation. This study illustrates the complex relationship between handedness and language development and emphasizes the need to take the different functions of pointing gestures into account.Ó 2011 Elsevier Inc. All rights reserved. IntroductionA small body of research has described the development of hand preference in relation to language development, although this topic represents a significant source of information for assessing developmental changes of these two main functional asymmetries. Because the use of one hand for a specific activity mostly reflects the predominant involvement of the contralateral hemisphere, this measure provides an innovative means for investigating its relations with the cerebral control of speech during development. Moreover, different measurements of handedness may allow us to determine whether manipulative activities and communicative gestures are linked to speech at varying degrees. In the Contents lists available at ScienceDirectJournal of Experimental Child Psychology jo urnal homepage: www.elsevier.co m/locate/jecp current study, language level and hand preference for both bimanual manipulation and pointing gestures were measured longitudinally in toddlers between 13 and 21 months of age in an attempt to unravel the complex relationships between language acquisition and the development of handedness. We focused on a key period of language development, namely the lexical spurt, whose onset was expected to be more closely linked to hand preference for pointing than to handedness for noncommunicative actions in the course of development. Moreover, speech-gesture relationships were expected to vary depending on the function served by pointing gestures.