Extended visual fixation in young infants: look distributions, heart rate changes, and attention.

Visual fixation in infants from 3 to 6 months of age was examined for its fit to the theory of "attentional inertia." This theory posits that during the progression of a look there is increasing attention toward the stimulus and an "inertia" to continue looking. An extended audiovisual stimulus was presented for 20 min to infants while fixation was videotaped and heart rate (HR) was recorded. Consistent with the attentional inertia theory, look duration toward the stimulus had a lognormal distribution. Hazard functions describing these distributions showed a decreasing conditional probability of looking away with increases in look duration. Look onset and stimulus changes that occurred within a look were accompanied by HR deceleration. The average HR level continued to decrease over the duration of a look and returned to prestimulus level immediately prior to the fixation offset. Infant fixation has characteristics similar to fixation in children and adults, and attention appears to increase over the course of a look in young infants.