| Current theories of mature selective attention include an inhibitory component which limits attention paid to distracting stimuli. Although strides have been made in understanding selective attention in infants, little research has focused on the development of the inhibitory aspects of attention, especially in infants under 6 months. Current models of visual attention development posit that the neurological substrates known to underlie endogenous visual attention control are not functionally mature until sometime between 3.5 and 6 months. However, infants as young as 2 months can make anticipatory saccades, which require endogenous attention control. Current models also postulate that the same substrates that underlie voluntary attention inhibition also play a role in releasing infants from sticky fixation. The present study sought to determine the age at which infants are first able to exercise voluntary inhibition of shifts of visual attention, and whether the onset of this ability is associated with the decline of sticky fixation. In the first experiment, 2-, 3-, and 4-month-olds were reinforced for sustaining visual fixation of a stimulus in the presence of a distractor. Only the 4-month-olds succeeded. Experiment 2 applied the same procedure to a longitudinal sample and found no evidence of inhibitory attention control at 2 months, mixed evidence at 3 months, and clear evidence of inhibitory attention control at 4 months. Correlation analyses found no association between sticky fixation and attention control. Examination of the developmental trajectory of attention control found substantial individual differences among trajectories. In both experiments, infants reduced total fixation of distractors mainly by reducing the duration of individual fixations of the distractor rather than by reducing the number of fixations. Instead of inhibiting eye movements, these infants may have regulated the quality of attention paid to each stimulus by prolonging sustained attention to reinforced stimuli and curtailing sustained attention to distractors. These results suggest that the bases for generating endogenous shifts of visual attention may be different from those that allow the endogenous inhibition of shifts of visual attention. |
