Local and Global Face Identity Discrimination in Children, Adolescents and Adults with Autism Spectrum Disorder

Background:

Autism Spectrum Disorder (ASD) is differentiated from other neurodevelopmental disorders by its unique perceptual phenotype (Bertone et al, 2010), defined by a relative facility for processing non-social, spatial information with concurrent difficulty in perceiving complex, socially laden information exemplified by face perception (Simmons et al., 2009). Some suggest that atypical face perception in ASD has a perceptual origin, resulting from abnormally local or detailed processing strategies (Behrmann et al., 2006) that change with age (Guy et al., 2016). The ability of high-functioning autistics to discriminate facial identities is selectively decreased when access to local facial cues is minimized (Morin et al., 2015). However, these results, are based on autistics who score average or higher on IQ tests; therefore, little information is available for individuals who are ‘lower functioning’.

Objectives:

The objectives of this study were twofold:

1. When access to local cues are diminished, do autistics who are ‘low functioning’ exhibit an atypical performance profile?
2. Does identity discrimination ability differ as a function of age, and if so, are such differences related to the differential use of local vs. global facial processing?

Methods:

Nineteen autistics (17 male, 2 female), aged between 9 and 21 years, completed the Wechsler Abbreviated Scale of Intelligence (WASI-2) as well as the Social Responsiveness Scale (SRS-2). Participants then completed a simple, 2AFC facial identity discrimination task where they answered ‘same’ or ‘different’ to two synthetic face stimuli (Wilson et al, 2002) presented simultaneously on a computer screen. First, face pairs were presented front-facing, allowing for identity judgements to be based on local facial cues (e.g., comparing noses). The second condition presented a stimulus view-change, where face pairs had one front facing and one side facing stimulus (20 deg.), resulting in a decreased access to local information, and a greater reliance on a global analysis to complete the task.

Results:

A 3 x 3 ANOVA (condition x developmental group) revealed a significant effect of condition (F (2, 32) = 38.4, p <0.001), suggesting that autistics found the front-front condition (facilitating local strategies) significantly easier than the front-side condition (facilitating global strategies). A significant correlation was found between chronological age and performance in the front-front condition (r = 0.49, n = 19, p = 0.03) despite no significant correlation with IQ or SRS scores.

Conclusions:

Results reveal a similar performance profile for individuals on the ‘lower functioning’ spectrum of ASD compared to individuals who are ‘high-functioning’ (e.g. Guy et al 2016). Thus, this study contributes to understanding face perception in autistics with low IQ: a group who are less well defined in ASD visual perception research. Results indicate a divergent developmental trajectory, upon which, locally-oriented face perception improves as a function of age while global processing does not. Eye tracking data was also collected for this study and so future developments of this project will seek to assess whether atypical face perception in ASD may have a non-social origin by examining these data in conjunction with objective viewing strategies.