Abnormal Size-Dependent Modulation of Motion Perception in Children with Autism Spectrum Disorder (ASD)

Abstract

Excitation/Inhibition (E/I) imbalance in neural networks is now considered among the core neural underpinnings of autism psychopathology. In motion perception at least two phenomena critically depend on E/I balance in visual cortex: spatial suppression (SS), and spatial facilitation (SF) corresponding to impoverished or improved motion perception with increasing stimuli size, respectively. While SS is dominant at high contrast, SF is evident for low contrast stimuli, due to the prevalence of inhibitory contextual modulations in the former, and excitatory ones in the latter case. Only one previous study (Foss-Feig et al., 2013) investigated SS and SF in Autism Spectrum Disorder (ASD). Our study aimed to replicate previous findings, and to explore the putative contribution of deficient inhibitory influences into an enhanced SF index in ASD-a cornerstone for interpretation proposed by Foss-Feig et al. (2013). The SS and SF were examined in 40 boys with ASD, broad spectrum of intellectual abilities (63 < IQ < 127) and 44 typically developing (TD) boys, aged 6-15 years. The stimuli of small (1°) and large (12°) radius were presented under high (100%) and low (1%) contrast conditions. Social Responsiveness Scale and Sensory Profile Questionnaire were used to assess the autism severity and sensory processing abnormalities. We found that the SS index was atypically reduced, while SF index abnormally enhanced in children with ASD. The presence of abnormally enhanced SF in children with ASD was the only consistent finding between our study and that of Foss-Feig et al. While the SS and SF indexes were strongly interrelated in TD participants, this correlation was absent in their peers with ASD. In addition, the SF index but not the SS index correlated with the severity of autism and the poor registration abilities. The pattern of results is partially consistent with the idea of hypofunctional inhibitory transmission in visual areas in ASD. Nonetheless, the absence of correlation between SF and SS indexes paired with a strong direct link between abnormally enhanced SF and autism symptoms in our ASD sample emphasizes the role of the enhanced excitatory influences by themselves in the observed abnormalities in low-level visual phenomena found in ASD.

Keywords: autism spectrum disorders (ASD); children; excitation/inhibition balance; motion perception; spatial facilitation; spatial suppression.

Figure 1

Experimental trial. Type of stimuli, used in the experiment (A) and schematic representation of the experimental trial timeline (B).

Figure 2

Size-dependent modulation of motion direction discrimination thresholds. The mean thresholds for ASD (red) and TD (blue) groups, obtained under high (A) and low-contrast conditions (B). Note that for demonstration purpose, threshold values are represented on y-axis in milliseconds along the log-transformed scale.

Figure 3

Relation between spatial suppression and spatial facilitation indexes in TD (A) and ASD (B) children. Note that although the average indexes of contextual modulation assessed under high and low-contrast conditions respectively are expected to be of opposite signs, for both conditions equally the greater values signified a shift of a balance toward relatively stronger suppression and weaker facilitation, and, vice versa, the lower individual indices reflected enhanced facilitation and reduced suppression. Therefore, positive correlation between spatial suppression and spatial facilitation found in TD children indicates that on the individual level stronger spatial suppression under high contrast is associated with weaker facilitation under low contrast condition.

Figure 4

Spatial facilitation and ASD symptoms. Correlation between SF index and SRS scores (A) and sensory processing abnormalities—low registration scores (B) in ASD children. Note that lower SF scores indicate stronger spatial facilitation. Since higher scores on SRS and lower scores on low registration correspond to higher symptoms severity, the direction of their relationships with SF is the same, despite an opposite sign of their correlations.