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Typical and Atypical Development of the Kinesthetic Percept: Noisy, Random and Restricted Proprioception in Autism

Typical and Atypical Development of the Kinesthetic Percept: Noisy, Random and Restricted Proprioception in Autism

In 78 participants (34 with a diagnosis of ASD) we studied the stochastic patterns of velocity-dependent behavioral variability, where the minute fluctuations in hand pointing movements (micro-motions) were treated as a form of re-afferent proprioceptive input. Subjects ranged from 3 years of age to 61 years of age. This is the empirical estimation of each individual's probability distribution as a member of the 2-parameter continuous Gamma family of probability distributions. Each point is an estimate using Maximum Likelihood Estimation of the shape and scale parameters of the Gamma probability distribution plotted as points on the Gamma plane. This plot localizes each individual uniquely. The scatter from the normalized peak velocity parameter (properly normalized to avoid limb-size-difference effects) revealed a scaling power law with self-emerging clusters that shifted with age (see legends). In the typical course of development humans go from random, noisy and restricted proprioception to a stable kinesthetic percept with highly reliable and predictive power as attested by the Fano Factor (variance to mean ratio) and the location to the right of the Gamma plane. This is not the case in autism spectrum disorders where the proprioception remains at the level of a three year old typically developing infant: random, noisy and restricted. Under these conditions they cannot use proprioceptive input to help with movement self-regulation and volitional control, nor can they anticipate the consequences of impending actions and weigh the risks and benefits of impending decisions. They must live in the "here and now" barely relying on the restricted proprioceptive information that they receive from the external input, the statistics of which they cannot embody. No wonder about their extreme reliance on sameness. Every new information most bring more uncertainty to an already corrupted signal and amplify the sensory-motor noise of their system. Typical proprioception turns predictive and can be used to anchor and modulate new contextual variations but in autism proprioception does not undergo the maturation required to acquire a "kinesthetic prior". The regulatory mechanism is broken. We are changing that with a new generation of therapeutic interventions and objective metrics to dynamically track progress. At the behavioral level our empirical results lend support to a contemporary theory of the neurobiology of autism presenting an alternative view that connects the system across levels from molecules to behavior and offers testable predictions (Markram & Markram 2010). We offer a new statistical platform to probe the system's noise and signal at various functional levels and use spontaneous behavioral variability as a proxy to induce intentionality in their actions.

Keywords: autism, Autism Spectrum Disorder, objective metrics, Proprioception, kinesthetic perception, Statistical Distributions, Statistical Mechanics, power-law, scaling exponents, typical development, Atypical Development, Movement Disorders, sensory motor integration, sensory motor learning, sensory motor training, Diagnosis, Computer-Assisted, Diagnosis, Differential, Clustering analysis, Automatic Data Processing, Movement, reaching movements, speed control, peak velocity, velocity dependent parameters

Posted by: Elizabeth B Torres

Posted on: 19 Mar 2013

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