Reduced Spatial Suppression in ASD Children

Background: Paradoxically, as stimuli size increases the motion perception of high-contrast gratings deteriorates. This phenomenon is called “spatial suppression” and is believed to reflect center-surround neural inhibition (Tadin et al., 2003). The abnormal excitation/inhibition (E/I) balance has been implicated in Autism Spectrum Disorder (ASD), predicting the reduced spatial suppression in this population. To the best of our knowledge only one study examined spatial suppression in ASD individuals (Foss-Fieg et al., 2013).  Although the reduction of spatial suppression in high-contrast stimuli was not found in this study, the authors suggested that reduction of spatial suppression in ASD can be masked by attenuated gain control, an inhibitory mechanism that underlies saturation of neural responses at high contrast, which characterize their ASD subjects. Additionally, the general enhanced sensitivity to motion of high-contrast stimuli in ASD was reported. Noteworthy, this study comprised only high-functioning ASD children with extremely high IQ scores (116.7±12.4), questioning the generalizability of the results into broader ASD sample.

Objectives: The aim of our study was to examine the spatial suppression and gain control in a broader sample of ASD children with wider range of IQ scores. 

Methods: Subjects were 22 ASD boys and 32 TD boys, aged between 6 and 15 years with IQ ranging from 62 to 136: intellectual ability was assessed by the Kauffman Assessment Battery (Kauffman&Kauffman, 2004). Experimental groups did not differ by chronological age, but mean IQ score was higher in TD than ASD children (117.5±12.0 and 90.9±19.8, respectively). The experimental procedure was similar to those used by Foss-Feig et al., 2013. The stimuli were the drifting vertical sine wave gratings of either small (2°) or big (12°) size, presented in high- (100%) or low- (1%) contrasts. The duration of stimuli presentation was adjusted using two interleaved one up two down staircases that converged on 71% correct performance. Participants were asked to judge the direction of motion. The logarithm of the obtained threshold was taken as a dependent variable for ANOVA analysis performed separately for high- and low- contrast condition with stimuli Size as within-subject factor and Group as between subject factor. To examine for gain control ANOVA with Contrast as within-subjects factor was applied to the thresholds for small stimuli obtained in low and high contrast blocks. 

Results: In high-contrast condition the was significant Size by Group interaction (F(1,52) = 5.49, p = 0.023, η2 = 0.094), with ASD children having smaller difference between thresholds obtained for small and big stimuli (spatial suppression) as compared to TD boys (log scaled: 0.18±0.19 and 0.30±0.19, respectively for ASD and TD). No group difference in low-contrast condition was found. The group also did not differ either in gain control or in general sensitivity to motion.  

Conclusions: Our study provides evidence for a reduced spatial suppression in a representative sample of ASD boys comparing to their TD peers.