Spontaneous Oculomotor Movement and Stereotyped and Rigid Behaviors: Results from the ABC-CT Feasibility Study

Background: Individual variability in oculomotor movements such as blinks and saccades has been noted between individuals with autism spectrum disorder (ASD) and typically developing peers (TD) and can reflect variability in underlying biological systems. Characteristics of blinks and saccades, such as frequency and regularity, may be linked to processes and behaviors relevant to ASD, including motor stereotypies, cognitive rigidity, and attentional processing. However, there is scant research linking variability in spontaneous eye-movements and clinically meaningful individual differences. Examining the relationships among these traits and individual variation in the properties of blinks and saccades may contribute to understanding of oculomotor features in ASD and cognitive processing more generally. Features that are strongly differentiated by group or degree of stereotyped and rigid behaviors may serve as potential stratification biomarkers.

Objectives: This study examines relationships among oculomotor characteristics, such as spontaneous blink rate and saccadic rhythmicity, and stereotyped and rigid behaviors in children with ASD and their TD peers.

Methods: Remote eye-tracking data were collected from 51 participants (ASD: n=25, 20 male; TD: n=26, 17 male; ages 4-11, mean age = 7.17) using an SR Eyelink 1000+ while participants freely viewed static images. Blink rate was calculated as the average number of blinks per second across all stimuli. Rhythmicity of eye movements was examined in the frequency domain; power spectra were generated from 250ms segments of data and amplitude was extracted for frequencies between 4 and 10 Hz based on prior studies of saccadic rhythmicity. Stereotypy and rigidity were measured using the stereotypy subscore of the ADOS-2, the frequency of restricted behavior subscale of the Autism Impact Measure (AIM), and the Behavior Assessment System for Children (BASC-3) adaptability and attentional control subscales.

Results: One-way ANOVA indicated a statistically significant difference in blink rate between diagnostic groups (F(1,49)=6.097, p=0.017), such that individuals with ASD blinked more than TD controls. However, no main effects of stereotypy or rigidity were seen in multiple regression models examining the effect of diagnosis, behavioral measures, and their interactions on blink rate. Saccadic rhythmicity was associated with frequency of restricted behavior as measured by the AIM, such that, among individuals with ASD, those with more regular eye movements scored higher on the AIM (β=45.57, p=.034). No independent effect of restricted behavior on saccadic rhythmicity was seen across diagnostic groups. A one-way ANOVA showed a significant difference in the power of the 4-10Hz frequency component between diagnostic groups (F(1,49)=25.67, p<0.01) suggesting that individuals with ASD exhibited a higher frequency of saccadic eye movements.

Conclusions: Preliminary analyses suggest that blink rate and frequency dynamics of spontaneous eye movements differ in children with ASD and their TD peers. Among children with ASD, saccadic rhythmicity exhibited a stronger frequency component from 4-10 Hz, which was further modulated by the degree of restricted behavior they display. Further research linking these measures to other measures of cognitive processes and to stereotyped behaviors may extend understanding of ways spontaneous eye-movements underlie stereotypical movement and rigidity of cognition and behavior in ASD.