Dot Prototype Formation in Infants: A Comparison of Infants At High- and Low-Risk for Autism Spectrum Disorder

Background:  Categorization is a critical cognitive ability that reduces demands on memory and allows individuals to focus on important aspects of objects while ignoring irrelevant details. Critical to categorization is the ability to abstract prototypes.  Infants are able to form categories and prototypes of dots, objects, and faces within the first year of life (de Haan et al., 2001; Strauss, 1979; Younger 1990; Younger & Gotlieb, 1988). However, there is growing evidence suggesting that individuals with autism spectrum disorders (ASDs) have difficulty with aspects of categorization and prototype formation (Gastgeb et al., 2006, 2009, in press; Klinger & Dawson, 1995, 2001; Vladusich et al., 2010).  Despite this, little is known about the origin of these difficulties.

Objectives:  To examine the origin of prototype formation difficulties by investigating dot prototype formation ability in 6-, 11-, and 16-month-old infants who were at either high- or low-risk for developing ASD.

Methods:  Infant siblings of children with ASD (high-risk infants; HR) and infant siblings of typically developing children (low-risk infants; LR) matched on verbal, nonverbal, and total DQ scores on the Mullen were tested using a procedure modeled after Younger & Gotlieb (1988). Infants were shown six familiarization stimuli from a dot pattern category and then four test stimuli.  Familiarization stimuli consisted of two paired dot patterns.  First, two within category test trials were presented (prototype paired with a previously seen dot pattern), then two between category test trials were presented (prototype paired with a dot pattern from a novel category).  Eye-tracking was used to determine the infants’ fixation times.

Results:  For within category trials, neither LR nor HR infants showed evidence of prototype formation at 6 months.  However, LR infants demonstrated a novelty preference for the previously seen dot patterns at 11 and 16 months, indicating that they formed a prototype. HR infants did not demonstrate a novelty preference for either dot pattern at any age.  For between category trials, all infants at all ages demonstrated a novelty preference for novel dot patterns, indicating that even though HR infants did not show evidence of prototype formation, they formed a category of dot patterns.  The eye-tracking data indicated that group differences were not due to the amount of time spent looking at the familiarization dot patterns or differences in how extensively the infants scanned the dot patterns during test trials.

Conclusions:  Results are consistent with previous studies that found deficits in prototype formation in individuals with ASD and extend these deficits to HR infants.  Since the HR infants are yet not old enough to be diagnosed with respect to ASD, it is unknown whether prototype formation difficulties will be predictive of an ASD diagnosis or whether they represent difficulties present in the broader autism phenotype.  It is possible that the results are reflective of a general difficulty with implicit learning and reduction of information into a statistical summative or central representation in HR individuals and/or individuals with ASD.