Lateral preferences in food reaching and whole-body turning were assessed in 24 prosimian primates: 16 galagos (Galago moholi) and 8 mouse lemurs (Microcebus murinus). Reach and turn preference in the galago were examined using a single testing procedure; separate procedures were used to evaluate reach and turn preferences in the mouse lemur. The motoric requirements for both species were 1) reach into a Plexiglas container with a single hand for a food item and 2) execution of a whole-body rotation about the long axis of the body. Twenty-three of the subjects tested had a reach preference (15 right, 8 left preferent) and 22 a turn preference (1 right and 21 left preferent). No correlation between the direction of reach and turn preference was found for either species; however an association between right reach preference and female gender was found for the galagos. A species difference in the strength of lateralization was found, with the more bipedal species, the galago, more strongly lateralized in both measures. This result supports the hypothesis that the assumption of upright posture was an important factor in the phylogenetic development of primate lateralization.

Despite clear functional significance, understanding of exploratory behavior is hampered by the lack of a careful descriptive account. This article reports extensive descriptions of rats' behavior in a stable environment and after environmental change. For 7 nights, 12 male Long-Evans rats (Rattus norvegicus) were given access to a large arena. Subjects budgeted session time differently across days, spending less time in the home cage and more time interacting with objects. Locomotion and general activities were typically unchanged over days. Several measures of object interaction showed systematic changes across sessions for the nonmanipulable object but not for the manipulable object. Finally, exploratory and spatial locomotor patterns were modified in response to the addition or removal of objects. These results indicate that exploratory and investigatory behaviors are lawful and orderly expressions of spontaneous behavioral organization.

Laterality was assessed in 100 human (Homo sapiens) subjects through the use of five measures of motoric behavior in three categories: locomotor, manual, postural. Locomotor measures included leading limb for initiation of walking and whole-body turning. Performance and questionnaire measures were used to assess lateral hand bias. Postural bias was assessed as the weight distribution in quiet standing. Population-level biases on the manual and leading limb measures were to the right; on posture and turning, to the left. Locomotor measures were found to be altered by marching experience. Only the manual measures were correlated. We compare the results with those of nonhuman primate studies that have used similar measures and discuss some patterns of laterality common to human and nonhuman primates.

We thank Allyson J. Bennett and Peter J. Pierre for assistance with data transcription and many helpful comments and discussions and David R. Widman for his helpful criticisms of an earlier version of this article.

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