The influence of food material properties on jaw kinematics in the primate, Cebus.

OBJECTIVE: To quantify the impact of food material properties on temporal and spatial variables of chewing kinematics at the level of the feeding sequence, gape cycle, and gape cycle phases.
DESIGN: Three-dimensional kinematics were quantified from two adult, male capuchin monkeys (genus Cebus) while chewing on foods grouped by material properties into two categories, foods of high toughness and foods of low toughness.
RESULTS: Total sequence duration and the total number of chews in a sequence are significantly influenced by food material properties, with foods of high toughness having shorter sequence durations and lower total chew numbers per sequence. Mean cycle duration is not impacted by food material properties at the level of the sequence, but food group differences are found when each cycle is compared independently by food group. Prior to chew fifteen, foods of low toughness elicit significantly lower gape cycle durations and significantly lower vertical displacements of M(1). At the level of the chew phase, variance in slow close explains the majority of variance in chew cycle duration prior to chew thirteen, with foods of low toughness eliciting shorter slow close durations and smaller vertical displacements of M(1). The vertical displacement of M(1) throughout the chewing sequence is the primary spatial determinant of variance in the duration of slow close.
CONCLUSIONS: These data reveal that chewing behaviour in Cebus is temporally stereotyped at the level of the gape cycle, but temporally and spatially flexible within the cycle, at least partly due to central mechanisms of motor control.