Complexity analysis of head movements in autistic toddlers

Abstract

Background: Early differences in sensorimotor functioning have been documented in young autistic children and infants who are later diagnosed with autism. Previous research has demonstrated that autistic toddlers exhibit more frequent head movement when viewing dynamic audiovisual stimuli, compared to neurotypical toddlers. To further explore this behavioral characteristic, in this study, computer vision (CV) analysis was used to measure several aspects of head movement dynamics of autistic and neurotypical toddlers while they watched a set of brief movies with social and nonsocial content presented on a tablet.

Methods: Data were collected from 457 toddlers, 17-36 months old, during their well-child visit to four pediatric primary care clinics. Forty-one toddlers were subsequently diagnosed with autism. An application (app) displayed several brief movies on a tablet, and the toddlers watched these movies while sitting on their caregiver's lap. The front-facing camera in the tablet recorded the toddlers' behavioral responses. CV was used to measure the participants' head movement rate, movement acceleration, and complexity using multiscale entropy.

Results: Autistic toddlers exhibited significantly higher rate, acceleration, and complexity in their head movements while watching the movies compared to neurotypical toddlers, regardless of the type of movie content (social vs. nonsocial). The combined features of head movement acceleration and complexity reliably distinguished the autistic and neurotypical toddlers.

Conclusions: Autistic toddlers exhibit differences in their head movement dynamics when viewing audiovisual stimuli. Higher complexity of their head movements suggests that their movements were less predictable and less stable compared to neurotypical toddlers. CV offers a scalable means of detecting subtle differences in head movement dynamics, which may be helpful in identifying early behaviors associated with autism and providing insight into the nature of sensorimotor differences associated with autism.

Keywords: Autism; complexity analysis; computer vision; head movements.

Figure 1.

Illustrative screenshots: social movies were (a) Blowing-Bubbles, (b) Spinning-Top, (c) Rhymes, and (d) Make-Me-Laugh; nonsocial movies were (e) Floating-Bubbles, (f) Mechanical-Puppy, and (g) Dog-in-the-Grass-RRL.

Figure 2.

Facial landmarks representation. Circular points illustrate the position of the set of landmarks extracted. Axes illustrate the 3D system of coordinates associated to the face, with angles of rotation. The red colored landmarks were used to compute head movement dynamics.

Figure 3.

(a - g) Represents rate of head movement (left) and Mean_accel_HM (right) for each of the movies. Solid lines represent the median, and the faded overline represents the 1^st and 3^rd quartile. The number of participants in the autism and neurotypical groups varies across the movies since we have considered only individuals having at least 40% of valid data for the stimuli. The last plot (h) shows the mean value of Mean_accel_HM using all the tasks for social and nonsocial movies.

Figure 4.

(a - g) Representation of the MSE (left) across scales and the Integrated_MSE_HM (right). The number of participants in the autism and neurotypical (NT) groups varies across the movies since we have considered only individuals having at least 40% of valid data (Symbol: Δ→ p<.05). The last plot (h) shows the mean value of Integrated_MSE_HM using all the tasks for social and nonsocial movies.

Figure 5.

ROC curves of isolation and combination of Mean_accel_HM and Integrated_MSE_HM for (a) Rhymes and (b) all the social movies. CI=Confidence interval. AUC of the ROC for other movies are: Blowing-Bubbles: Mean_accel_HM:AUC=0.71,CI=[0.60,0.82], Integrated_MSE_HM:AUC=0.68,CI=[0.53,0.75], both:AUC=0.73, CI=[0.62,0.85]; Spinning-Top: Mean_accel_HM:AUC=0.68,CI=[0.54,0.77], Integrated_MSE_HM:AUC=0.67,CI=[0.51,0.75], both: AUC=0.71,CI=[0.52,0.78], Make-Me-Laugh: Mean_accel_HM AUC=0.70,CI=[0.52,0.71], Integrated_MSE_HM AUC=0.69,CI=[0.52,0.76]), both: AUC=0.72,CI=[0.56,0.78].