Individual differences in the visual attention of human infants: further evidence for separate sensitization and habituation processes.

How many and what kinds of processes mediate infant visual attention? Are they influenced by stimulus "complexity?" Analyses were performed on visual fixation data from ninety 4-month-old infants; the time each infant spent looking at a black and white checkerboard pattern containing either 4 x 4, 12 x 12, or 20 x 20 checks per picture was measured for eight 10-s trials, with 10-s interstimulus intervals (Kaplan & Werner, 1986). Correlational and factor analyses revealed one significant source of individual variability (or factor) in the 4 x 4 data, and two significant sources in the 12 x 12 and 20 x 20 data. One factor gained strength over progressive trials and accounted for decreases in looking time. A second factor gained strength over the first few trials, then lost strength over the remaining trials, and accounted for initial increments in looking time. The two factors are consistent with a dual-process model of infant response dynamics; the first may represent habituation, a decremental process, and the second may represent sensitization, an incremental process that is activated by "complex" stimuli.