Head cocking in galagos

Abstract

Abstract. Contrary to an earlier report that galagos do not perform head cocking, which is a rotating movement of the head around its rostrocaudal axis while orienting in a fixed direction, this study documents frequent head cocking in galagos when viewing novel stimuli. Adult and infant lesser bushbabies, Galago moholi, were presented with a variety of stimuli. Frequencies and angles of head cocking were scored. The head-cock was characterized by a fast saccadic rotation of the head, usually to an angle of approximately 45° or 90° to the vertical, a brief period of fixation in the cocked position followed by a saccadic return. Head cocking to a 180° angle (inversion of the head) occurred occasionally. Adult females head-cocked more frequently than males, and infants more frequently than adults. The adults head-cocked most frequently to a live prey stimulus. A novelty effect of stimuli was suggested in that head cocking decreased in frequency from the first to the second presentation. The perceptual mechanisms served by head cocking are discussed. As galagos have ocular dominance columns in the visual cortex, the hypothesis that head cocking somehow compensates for their absence is clearly disproves. Alternative hypotheses relating head cocking to the presence of a cruciform-shaped area centralis in the retina or the shape of the pupil are outlined. The possible contribution of auditory perception is also discussed, and ear movements during head cocking are characterized.