The posterior visual spatial attention system involves a number of separable computations that allow orienting to visual locations. We have studied one of these computations, inhibition of return, in 3-, 4-, 6-, 12-, and 18--month-old infants and adults. Our results indicate that this computation develops rapidly between 3 and 6 months, in conjunction with the ability to program eye movements to specific locations. These findings demonstrate that an attention computation involving the mid-brain eye movement system develops after the third month of life. We suggest how this development might influence the infant's ability to represent and expect visual objects.

Three aspects of the development of visual orienting in infants of 2, 3, and 4 months of age are examined in this paper. These are the age of onset and sequence of development of (1) the ability to readily disengage gaze from a stimulus, (2) the ability to consistently show “anticipatory” eye movements, and (3) the ability to use a central cue to predict the spatial location of a target. Results indicated that only the 4--month-old group was easily able to disengage from an attractive central stimulus to orient toward a simultaneously presented target. The 4--month-old group also showed more than double the percentage of “anticipatory” looks than did the other age groups. Finally, only the 4--month-old group showed significant evidence of being able to acquire the contingent relationship between a central cue and the spatial location (to the right or to the left) of a target. Measures of anticipatory looking and contingency learning were not correlated. These findings are, in general terms, consistent with the predictions of matura-tional accounts of the development of visual orienting.

Spontaneous alternation is a reduced tendency to return to the same location on successive trials. It is measured in rats in a T maze and is thought to depend on an intact hippocampus. In human infants, we measured alternation in the tendency to reach toward one of two identical toys placed in locations to the left and right of midline. Infants at 6 months returned to the same side as frequently as they alternated, but 18--month-old infants showed a significant alternation pattern. At 6 months, infants show inhibition of return, but do not show alternation in motor behavior; at 18 months, infants show both, but they are negatively related. These data suggest that preference for novelty may rest on different internal mechanisms even in quite similar tasks, and suggest that whereas inhibition of return is related to control by the posterior attention network, spontaneous alternation may be related to inhibitory control by the anterior attention network.