Objectives: To determine whether the infant siblings of children with autism have enhanced visual search relative to typically developing infants. Such an examination can enrich our understanding of the broader autism phenotype, and can help pinpoint when enhanced search abilities first emerge in autism.
Methods: We observed 22 infant siblings of children with autism (five 6-month-olds, nine 12-month-olds, and eight 18-month-olds) and 24 typically developing infants (five 6-month-olds, nine 12-month-olds, and ten 18-month-olds).
Each stimulus consisted of a “plus” sign target among “L” distractors; targets were equidistant from the center. In the Random condition, 7, 13, or 26 distractors were distributed randomly around the screen; in the Circle condition, 4, 7 or 13 distractors were distributed in a circle. All Random condition stimuli were presented before Circle condition stimuli.
Before each 2 sec stimulus, an attention-getter attracted the infant’s attention to the center of the screen. Infants’ gaze (onset and duration of fixations) was measured with Tobii eye-trackers. ANOVAs and independent-samples t-tests were conducted on accuracy (number of targets found) and time-to-target (time before the infant fixated the target). Data from trials lacking an adequate central fixation were excluded.
Results: The ANOVAs found no significant differences between the groups; with a Bonferroni correction, the t-tests also did not find significant differences. For each group, accuracy in both Random and Circle conditions increased with age and with fewer distractors (p < .01). In an overall ANOVA with the groups taken together, in the Circle condition, time-to-target decreased with fewer distractors (p = .009). Accuracy in the Circle condition showed a trend towards interaction between age and risk category (p = .07), such that typically developing infants were worse than infant siblings at 6 months but better at 18 months. An unexpected result was a positive correlation in infant siblings at 12 months between average time-to-target in the Circle condition and total scores on the Autism Observation Scale for Infants (12month), r = .718, p < .05, N=10.
Conclusions: In this preliminary data, there were no significant differences between the two groups. This may be because enhanced visual search is specific to autism rather than to the broader autism phenotype, because it develops after 18 months, because it is not evident in implicit visual search paradigms or with the measures used, or because of the small sample size. Ongoing data collection will include 24-month-olds and additional participants in all conditions, data analysis will include additional measures such as latency to target when that is the infant’s first fixation.