Visual Sensitivity In Adolescents with Autism Spectrum Disorders: Faces, Objects, and Contrast Sensitivity

Background: Children, adolescents and adults diagnosed with Autism Spectrum Disorders (ASD) generally display impaired face processing, both in perceptual and neural imaging studies (see Schultz, 2005 for review). Whether individuals with ASD exhibit typical face inversion effects is controversial (Teunisse & de Gelder, 2003, Webb et al., 2009).  In addition, there has been speculation that subcortical Magnocellular (M) vs. Parvocellular (P) pathways may be atypical in ASD (see Koldewyn and Rivera, 2005).  Recent research from our laboratory looking at these pathways in adolescents with ASD suggested heightened P pathway functioning in unaffected siblings as a possible protective factor for this group (Koh, Milne, & Dobkins, 2010).

Objectives: In the current study, we 1) collected discrimination thresholds for faces vs. non-face objects (cars), and 2) measured M vs. P pathway sensitivities, to determine whether they could account for group differences in face vs. object discrimination.

Methods: Our study included 20 typically developed adolescents (TD), 7 unaffected adolescent siblings of individuals with ASD (SIBS), and 12 adolescents with ASD. We obtained discrimination thresholds for upright and inverted faces and non-face objects (cars) by asking participants to match a test morph to one of two images (A vs. B), while an adaptive staircase varied the percent of A vs. B in the test morph. We also obtained contrast sensitivities for luminance (light/dark, M pathway) and chromatic (red/green, P pathway) sinusoidal gratings (0.27 cycles/degree, 4.2 Hz), by using an adaptive staircase.  The diagnosis of ASD was confirmed with the ADOS, SRS and SCQ.

Results: A two-factor ANOVA including just the TD and ASD groups showed a main effect of subject group in the face/object discrimination task (the ASD group underperformed the TD group, p = 0.008), but this was driven by a significant difference between TD and ASD for face discrimination only (TD vs. ASD: faces, p = 0.003; objects, p = 0.308; subject group x stimulus type interaction, p = 0.042). On the luminance/chromatic contrast sensitivity task, the ASD group underperformed the TD group (p = 0.044). However, there was no interaction between subject group and stimulus type, indicating that the group difference was the same for luminance and chromatic stimuli. In both experiments, there were no significant differences between SIBS and TD or SIBS and ASD.

Conclusions: gTo our knowledge, this is the first well-controlled demonstration of deficits in face discrimination in adolescents with ASD.  Because this deficit was selective for faces, and not objects, we believe the effect cannot be accounted for by the overall deficient contrast sensitivity in the ASD group (which would have predicted impairments in both face and object discrimination), and thus we believe the face deficit represents atypical functioning in face processing regions of the brain. Although we found no evidence of a protective factor for the P pathway in SIBS (i.e. no superiority in chromatic sensitivity, as in Koh et al., 2010), our sample size (n=7) was quite small.  Thus we may lack the power necessary to detect an effect at this time.