Introduction

Over the last two decades, it has been well established that there are a variety of forms of structural and functional lateralization in a number of avian species, including chicks (reviewed by Andrew, 1988, 1991; Rogers, 1995, 1996), pigeons (Güntürkün, 1997b), canaries (Nottebohm, 1977), zebra finches (Alonso, 1998) and marsh tits (Clayton and Krebs, 1994). Among these avian species, the chick, Gallus gallus domesticus, has been used as a model to study how hormones and early experience interact to influence the development of brain lateralization. In this chapter we review a number of studies that have examined the influence of light exposure prior to hatching and of steroid hormones on the development of asymmetry of the visual pathways and lateralization of visual behaviour.

Although the chick has been used extensively in studies of learning, memory formation, visual lateralization and visual neurone development, knowledge of the organization of the visual pathways in the chick is limited. Until recently, most knowledge of the organization of avian visual pathways came only from studies of the pigeon (reviewed by Güntürkün et al., 1993; Bischof and Watanabe, 1997), and it was generally assumed that the visual system of chicks had the same organization as that of the pigeon or one very similar to it. However, our recent studies have shown there are some clear differences between the chick and the pigeon in the organization of the central visual pathways (Deng and Rogers, 1998a, 1998b).