Participants included toddlers with ASD (age
M = 22.39, SD = 3.02 months,
n = 112), DD (age
M = 21.71, SD = 3.38 months,
n = 36), and TD (age
M = 21.89, SD = 3.39 months,
n = 163). ASD participants were recruited at a university-based research clinic specializing in the early differential diagnosis of autism and other developmental disorders. The study of children with ASD at this early age afforded the examination of visual gaze strategies typically at the age of first diagnosis and therefore before the potential secondary effects of interventions would likely take hold. The TD and DD toddlers had no family history of autism in first or second degree relatives. Developmental skills were evaluated using Mullen Scales of Early Learning (MSEL, 1995 [
19]); (see Table
1). The MSEL captures developmental functioning in nonverbal (fine motor and visual reception) and verbal (receptive language and expressive language) domains. For this study, developmental quotients were computed for the verbal (VDQ) and nonverbal (NVDQ) scores. The severity of autism symptoms was measured using the Autism Diagnostic Observation Schedule-Generic Module 1 (ADOS-G [
20,
21]); (see Table
1). The ADOS-G provides scores in the domains of social affect (SA) and restrictive and repetitive behaviors (RRB), as well as a total score reflecting the sum of SA and RRB scores. The three groups did not differ with regard to age (
F(2, 308) = 1.00,
p = .37). The ASD group consisted of 85.7% males, as compared to 88.9% in DD and 59.5% in TD groups (
χ2(2) = 28.4,
p < .01). The ASD and DD groups were comparable with regard to MSEL NVDQ (
p = 0.25), and both had lower scores than the TD group (
ps < .001). The MSEL VDQ of the ASD group (
M = 55.8, SD = 2.4) was significantly lower than that of the TD (
p < .001) and DD groups (
p < .01). The VDQ of the DD group was also lower than that of the TD group (
p < .001). All ASD diagnoses were based on clinical best estimate (CBE). In 79.5% (
n = 89) of cases, CBE was conducted in a follow-up visit at 36 months (mean age at eye tracking 22.5 months; at CBE 38.7 months); in the remaining 20.5% (
n = 23) of cases, CBE was conducted at the time of eye tracking (mean age 22.2 months). CBE was based on the direct assessment of developmental, social, communication, and adaptive skills, as well as review of developmental and medical history, by a multidisciplinary team of expert clinicians. Standard measures included the ADOS-G [
20,
21], MSEL [
19], PLS-5 [
22], Vineland [
23], and ADI-R [
24]. Previous studies have indicated that CBE diagnoses of ASD in clinic-referred children are highly stable (~ 90%) between the second and third year of life [
25‐
27]. Given the large size of our samples, this is unlikely to significantly impact study results. The DD group included toddlers with a score less than 1.5 SDs below age-norms on one or more subscales of the MSEL and included toddlers with global developmental delays or language delays. Children in the TD group exhibited typical developmental profiles. This research was approved by the Yale University Institutional Review Board, and informed consent was obtained from the legal guardians of all participants enrolled in this study. Subsets of this data have been previously reported in [
3,
9,
28].
Table 1
Sample characterization
Male | 85.7% | 88.9% | 59.5% |
| N | Mean | SD | N | Mean | SD | N | Mean | SD |
Age (months) | 112 | 22.39 | 3.02 | 36 | 21.71 | 3.38 | 163 | 21.89 | 3.39 |
MSEL NVDQ | 110 | 82.70 | 16.67 | 36 | 85.86 | 11.81 | 161 | 109.96 | 13.00 |
MSEL VDQ | 110 | 55.84 | 30.97 | 36 | 69.76 | 16.89 | 154 | 111.34 | 21.23 |
ADOS SA | 109 | 13.35 | 4.66 | 35 | 5.83 | 3.97 | – | – | – |
ADOS RRB | 109 | 4.07 | 2.03 | 35 | 1.37 | 1.52 | – | – | – |
ADOS TOTAL | 109 | 17.42 | 5.69 | 35 | 7.20 | 4.52 | – | – | – |