Lateral Preferences in Monkeys

Abstract

AbstractHand preferences have been observed in a group of 48 monkeys. It is found that practice in manipulation increases the proportion of animals showing strong and consistent preferences and reduces the initial predominance of left preferences in this sample of animals to near equality with right. The proportion of animals showing strong and consistent preferences is low during initial somatosensory discrimination testing in the dark. The various kinds of change in preference observed on up to ten consecutive tests are analysed in some detail. Thus a full reversal is common in animals changing from a strong preference, whereas a strengthening of the same preference is common in animals changing from a weak preference. 45% of animals change their preference between the first and second test, but this proportion is progressively reduced, for example to 13% changing between tests 3 and 4. Finally the effects of various neurosurgical procedures on the preferences in 30 animals are tabulated. These comprise frontal, temporal or parietal cortical ablations and also section of one optic tract. Only the latter procedure gives rise to changes in hand preferences. It is concluded that the nature of the sensory control (whether visual or somatosensory, or if visual, whether confined to one half visual field) of a manual manipulation is another major determinant of hand preference.