Behavioural Lateralization in the Marmoset ('Callithrix jacchus')

Abstract

Lateralization of 21 common marmosets ('Callithrix jacchus') belonging to the colony at the University of New England was determined on a range of tasks. Hand preferences were measured during feeding. The hand preferred by subjects to hold food and take it to the mouth (simple food holding) was scored. Hand preferences were also measured on tests of visuospatial reaching that varied in the postural and spatial demands that they placed on the subjects. Leading-limb preferences (hand and foot) were recorded for walking, leaping arid landing. Two types of mouth function were examined: side-of-mouth preferences for chewing, on tests in which hand use was or was not required, and asymmetries of mouth opening in the production of a fear expression and species-specific vocalizations. The marmosets' eye preferences for viewing various stimuli were also determined. The presence or absence of hemispheric specialization, indicated by a group bias in the direction of lateralization, was determined for each function. Also, relationships between individual preferences displayed on the separate tasks were examined with a view to understanding factors influencing the development and evolution of lateralization. Individuals displayed strong hand preferences for simple food holding. These preferences developed by 5-8 months of age and remained consistent throughout the duration of this study, until 22 months of age for most subjects. However, there was no evidence of a group bias for simple food holding and therefore no handedness. Instead, preferences were bimodally distributed. Individuals also showed hand preferences on all of the tests of visuospatial reaching but, as for simple food holding, there was no group bias. Despite the absence of handedness on all tasks, it was found that most marmosets used one hand for simple food holding and the other for visually guided reaching. Thus, differential specialization of the hemispheres was present at an individual level, one hemisphere controlling simple food holding and the other visuospatial reaching.