Neuropsychologio, Vol. 27, No. 7, pp. 937-948, 1989. Printed in Great Britain. 0028~3932/89 s3.ca+o.o0 0 1989 Maxwell Pergamon Macmillan plc RIGHT HEMISPHERE ADVANTAGE FOR TOPOGRAPHICAL ORIENTATION IN THE DOMESTIC CHICK N. RASHID* and R. J. ANDREW School of Biological Sciences, University of Sussex, Brighton BNl 9QG, U.K. (Received 23 August 1988; accepted 19 December 1988) Abstract-When male chicks have to choose whether to orient by distant or proximal cues, chicks using the left eye (and so the right hemisphere) orient far better and make more use of distant cues than do right-eyed chicks. When both eyes are in use, left eye systems are mainly responsible for orientation, whereas right eye systems may concentrate on identifying food. Brief bias towards control of behaviour by the right eye system on day 8 allows it temporarily to be used successfully by the chick for orientation; apparently interference from the left eye system is reduced at this time. INTRODUCTION RIGHT HEMISPHERE ADVANTAGE in spatial analysis is generally accepted in human beings, and has been shown to affect ability to orient by, and recognize topographical features, as well as many other tasks involving spatial relations [lo]. Recent demonstrations of left visual field advantage in analysis of stimuli affected by blurring [13], which are compatible with asymmetries at a relatively peripheral level, nevertheless appear to be superimposed upon a right hemisphere advantage in higher level processing [S]. Some asymmetry of “spatial function” has been claimed for the rat on the basis of differential effects of right and left hemisphere insult on direction of turn [9]. BIANKI and FILIPPOVA [6] found a task depending on extrapolation of movement of an object in space to be more disturbed by right, than by left hemisphere inactivation in adult rats. It is then possible that some aspects of human spatial lateralization may occur in the rat. We report here left eye advantage in orientation by topographical features in the young domestic chick in a task which has the double advantage that it is a relatively natural one, and that it can be compared directly with similar human tasks. Decussation at the optic chiasma is virtually complete in birds, and it is likely (Discussion) that during independent scanning by the two eyes the input from the left eye is confined to structures of the right hemisphere and right brain stem (the “left eye system” (LES)). Specialization of the right hemisphere/LES for the analysis of spatial relations was suggested for the chick by earlier evidence [2] but this is to the best of our knowledge the first evidence for right hemisphere involvement in orientation by topographical features in a bird (or any vertebrate other than mammals). The basic properties of vertebrate lateralization and its course of evolution are likely to become clear only if they are studied in vertebrates lacking mammalian specializations such as obligate conjugate eye movements [S]. Our *Present address: Department of Zoology, University of Malaya, 59100 Kuala Lumpur, Malaysia 937