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Kinematic studies of reaching in human infants using two-dimensional (2-D) and three-dimensional (3-D) recordings have complemented behavioral studies of infant handedness by providing additional evidence of early right asymmetries. Right hand reaches have been reported to be straighter and smoother than left hand reaches during the first year. Although reaching has been a popular measure of handedness in primates, there has been no systematic comparison of left and right hand reach kinematics. We investigated reaching in infant rhesus monkeys using the 2-D motion analysis software MaxTRAQ Lite+ (Innovision Systems). Linear mixed-effects models revealed that left hand reaches were smoother, but not straighter, than right hand reaches. An early left bias matches previous findings of a left hand preference for reaching in adult rhesus monkeys. Additional work using this kind of kinematic approach will extend our understanding of primate handedness beyond traditional studies measuring only frequency or bouts of hand use. © 2011 Wiley Periodicals, Inc. Dev Psychobiol 54:460-467, 2012. [ABSTRACT FROM AUTHOR]

In human and chimpanzee infants, neonatal rightward supine head orientation bias predicts later right hand use preference. In an evolutionarily older primate species such as the rhesus monkey, a left hand preference has been reported, but there are no data on head orientation biases. Supine head orientation bias was measured experimentally in 16 rhesus monkey neonates and compared with prone head orientation bias as well as with various measures of hand use preference. A group-level leftward supine head bias was found that corresponded to greater activity in the left hand while supine; however, supine head orientation did not predict later hand preference as measured by reaching or manipulation on a coordinated bimanual task. These data suggest that a trajectory for handedness in rhesus monkeys may be different from that of humans and chimpanzees. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 53:246-255, 2011. [ABSTRACT FROM AUTHOR]