Johnson (1994) Visual attention and the control of eye movements in early infancy

Experiments concerned with the development of volitional (endogenous) control of eye movements (overt orienting) in infants are described. This evidence indicates that infants are capable of the voluntary control of eye movements by around 4 months of age. Next , experiments that attempt to measure covert shifts of visual attention in early infancy are reviewed, and the results of a study involving the exogenous cueing of covert attention reported. These results indicate that 4-month-old infants, like adults, show both facilitation and subsequent inhibition of responding to a cued spatial location. In contrast, a group of 2-monthold infants did not show these effects within the temporal parameters studied. Finally, I speculate on the underlying neural basis of these developments, and on their implication for the relation between covert shifts of attention and eye movements. It has become evident in recent years that there are multiple brain pathways involved in the control of eye movements and visual attention in adults (Schiller 1985; Posner and Peterson 1990). Investigating the sequential development of these pathways, and the construction of the visual attention system during ontogeny, may be informative given the obvious difficulty inanalyzing the complex combinations of hierarchical and parallel systems found in adults (see Johnson 1990, 1994). In this chapter I review studies and present new evidence on the ontogeny of both overt and covert aspects of visual orienting, focusing in particular on the transition from exogenous to endogenous control. I conclude by assessing the implications of these experiments on development for the debate in adult literature about the role of covert shifts of attention in saccade execution and planning. While our understanding of visual attention and orienting in adults is far from complete, a number of distinctions have been proposed that will be helpful in our analysis of the ontogeny of attention (see fig. 11.1). Eye movements that shift gaze from one location to another may be referred to as overt orienting. In contrast, shifts of visual attention between spatial locations or objects that occur independently of eye and head movements are referred to as covert (Posner 1980). Only in the past few years has work on covert shifts of attention in infancy been performed, and much of that work is reviewed in this chapter. Although shifts of covert visual attention are, by definition, dissociable from eye and head movements, they may be clearly related to 11.