Peripheral stimulus localization by infants: attention, age, and individual differences in heart rate variability.

The effect of attention to a focal stimulus on 3- to 6-month-old infants' peripheral stimulus localization was examined. Fixation was engaged on a central visual stimulus, and a stimulus was presented in the periphery after discrete time intervals (0 to 12 s) or until changes in heart rate (HR) occurred. Peripheral stimulus localization occurred less frequently when a significant HR deceleration had occurred (sustained attention) than when HR had returned to its prestimulus level (attention termination). A signal detection analysis showed that response bias was altered by attention and that during inattention infants with high HR variability were more likely to shift fixation away from the central stimulus independently of the presence of the peripheral stimulus. These data suggest that infant attention affects decision processes for continuing focal stimulus fixation rather than peripheral stimulus discriminability.