Spatial Uncertainty and Information Processing Speed in Infants and Adults: Age Differences in Saccadic Reaction Time Sensitivity.

Speed of information processing (SIP) as determined by response to spatial uncertainty is an important, perhaps limiting factor for cognitive development. With adults, although their manual response RTs for spatial uncertainty increase linearly with increasing choices, their saccadic RTs do not. In contrast, 7-month-old infants' saccadic RTs have been shown to increase with more target choices. What is the developmental course that enables this saccadic RT discrepancy between 7-month-oldsand adults? To address this question, the present study assessed adults' and 5- and 9-month-old infants' reactive saccades in a comparable choice reaction time task that varied spatial uncertainty. Both 5- and 9-month-olds' saccadic RTs increased linearly with more choice alternatives and uncertainty. Nine-month-olds' saccadic RTs increased at a shallower rate, however, approaching the slope of adults' saccadic RT function, which did not exhibit an increase with more uncertainty. Thus, there is a developmental trend for assessing spatial SIP with saccadic RTs. As infants age, saccadic responses become less sensitive to spatial uncertainty and approach adult-like performance. Decreasing saccade sensitivity may be due to developmental changes in the influence of response selection or in the functioning of inhibitory mechanisms.