Hand preferences and dexterities of captive patas monkeys

Evidence of Laterality in the Lowland Gorilla

The description of hand preference in the primates is at present sadly incomplete. In the lowland gorilla the consistency of the dextral preference across all tests is amazing and comparable to the human data. Similar analysis of the behavior of the orang-utan and a reexamination of the chimpanzee might present a coherent picture of homologous behaviours for the hominoidea.

Hand preference in unimanual and bimanual tasks and postural effect on manual laterality in captive red-capped mangabeys (Cercocebus torquatus torquatus)

Hand preference in 11 captive red-capped mangabeys (Cercocebus torquatus torquatus) was examined under different conditions: a free situation during spontaneous food processing, three different postural conditions (brachiating, and bipedal and tripedal standing), and a situation involving bimanual processing. Generally, individual laterality was found regardless of the task and behavior involved. However, the number of monkeys with hand preferences and the strength of the preference increased with the complexity of the tasks. The monkeys exhibited a significantly higher and positive mean manual preference index (HI) when they were hanging than when they were quadrupedal or sitting. The strength of manual preference (ABS-HI) was in turn higher when the monkeys were hanging or bipedal than when they were quadrupedal. The strength of manual preference was higher for both the bimanual and experimental tasks than for unimanual tasks and spontaneous activities. Although our sample was too small to allow us to make any generalizations concerning lateral preferences in red-capped mangabeys, we propose some hypotheses about the influence of posture stability and task complexity.

Hand preferences of rhesus monkeys on differing tasks

In a replication study, monkeys were tested for hand preference on three differing tasks: simple reaching for food presented on a board, choice of hand during a visual discrimination task and retrieval of food pellets from a row. Both laterality and degree of hand preference correlated significantly on two of the three tasks. Extremely little correlation was found across the other task combinations. Consistency of hand preference was greater within repetitions of a task than between any two tasks. The implication of these findings upon the search for a cerebral dominance underlying hand preference in the monkey is discussed.