Friday, May 18, 2012
Sheraton Hall (Sheraton Centre Toronto)
3:00 PM
J. L. Haworth1,2, W. Fisher
3, S. Vallabhajosula
1 and N. Stergiou
1,2, (1)Nebraska Biomechanics Core Facility, University of Nebraska at Omaha, Omaha, NE, (2)College of Public Health, University of Nebraska Medical Center, Omaha, NE, (3)Center for Autism Spectrum Disorders, Munroe-Meyer Institute, University of Nebraska Medical Center, Omaha, NE
Background: Preference for biological motion is characteristic of typically developing children but not for individuals with autism spectrum disorder (ASD) (Blake et al., 2003). However, this does not appear to be due to a sensory deficit in individuals with ASD, as they remain responsive to non-social, physical contingencies of object motion (Klin et al., 2009). These observations suggest that some underlying property of object motion must be salient or relevant to observers without ASD (but not those with ASD) that facilitates differentiation between biological and non-biological sources. Much work has sought to elucidate this property, as summarized in depth by Dakin and Frith (2005), including such factors as signal-to-noise interference and first/second order properties of stimulus motion. However, a definitive underlying characteristic of biological motion providing such visual salience has not been identified. Work in biomechanics has revealed that the kinematics resultant from biological sources of motion can be characterized by specific nonlinear measures of temporal structure of the movement variability; including entropy and local stability (Stergiou, et al., 2003). In fact, the health of a biological system is related to an optimal state of this variability; characterized by the presence of mathematical chaos examined in the movement over time. Contrastingly, stereotypic/rigid or noisy movements are not desirable. We hypothesize that the underlying deficit in the perception or identification of this variability may be characteristic of ASD, and the functional basis for the lack of discrimination of biological motion.
Objectives: To evaluate the perception and motor replication of visual stimulus movement variability; in adults with and without ASD.
Methods: Five adults without, and 2 with, ASD stood quietly on a force platform (AMTI, Accusway) and viewed an oscillating point-light, under two conditions. The motion of the point-light was driven either by sinusoidal (SN, stereotypic movement condition) or chaotic rhythm (CH, chaotic movement condition). Measures of postural sway and gaze (via eye-tracking) were collected during each condition for 1 minute at 50 Hz. Sample entropy was used to quantify the temporal structure of the variability in each measure.
Results: Individuals with ASD exhibited significantly different gaze response to both stimulus conditions, compared to those without ASD (SN, p=0.009; CH, p=0.013). Although this finding is clearly interesting and potentially important, our primary hypothesis was that individuals without ASD would show clear differentiation between the two conditions whereas those with ASD would not; which is what we observed. That is, adults without ASD exhibited greater complexity of their gaze behavior towards the more complex motion (CH, p=0.016), whereas adults with ASD did not differ in their gaze towards the two types of motion (p=0.544). Finally, results indicate that posture was not condition-responsive for persons with or without ASD.
Conclusions: This study provides preliminary evidence that the perception of the structure of movement variability differs for adults with ASD when compared with adults without ASD. This finding has potentially important implications relative to the lack of perception and motor response to biological motion reported for individuals with autism in prior research.
