Sensitization during visual habituation sequences: procedural effects and individual differences.

Although individual differences in visual habituation have long been interpreted in terms of processes derived from comparator theory, research over the last decade has suggested that arousal or arousability as manifest in sensitization may contribute to infants' attentional profiles, and thus, to individual differences in those profiles. We explored this possibility by habituating 4-month-old infants to 4 x 4, 10 x 10, or 20 x 20 checkerboards in a fixed-trial paradigm. The first specific aim was to examine the attentional characteristics of infants with habituation patterns showing sensitization versus those that did not. The second specific aim was to determine whether patterns of attention suggestive of sensitization effects reported in past research might be attributable to the use of illuminated interstimulus intervals (ISIs). Trends were observed for sensitization to occur more frequently with more complex than with less complex checkerboards. Infants who showed looking patterns characteristic of sensitization looked longer and did not habituate as readily as infants who did not show sensitization. Finally, different ISIs did not engender different levels of sensitization, but dark ISIs significantly increased infants' looking times to stimuli during trials.