The handedness of rhesus monkeys: II. Concurrent reaching.

Of 171 monkeys tested for handedness, 60 were found to make occasional bilateral concurrent reaches. These reaches accounted for only 1.3% of the total of 600 reaches observed for each animal. Younger animals were observed to make such reaches more frequently than older animals. Concurrent reaching was characterized by a lower degree of preference for the overall preferred hand than unilateral reaches made by the same animals at comparable periods of testing.