Individuals diagnosed with autism spectrum disorders (ASD) not only demonstrate language, social and sensory impairments but also movement abnormalities (DSM-IV, 2000
). In fact, movement abnormalities may be the hallmark of many diagnoses as restricted, repetitive, and stereotypical movements are commonly observed in individuals with ASD. Motor impairments of children/adults with autism may include gross motor coordination (e.g., Calhoun et al., 2011
), fine motor coordination (e.g., Gernsbacher et al., 2008
), motor stereotypies (e.g., Loh et al., 2007
), postural control (e.g., Molloy et al., 2003
; Minshew et al., 2004
), and/or motor apraxia (e.g., Ming et al., 2007
). A recent meta-analysis concluded that motor impairments are present across the spectrum with deficiencies reported in motor planning, sensorimotor integration, and motor execution (Fournier et al., 2010
). Inquiry into these movement aberrations appears warranted as these motor impairments may exceed other ability areas and influence both language and social integration (Piek and Dyck, 2004
Sensory processing deficiencies are commonly associated with ASD (Tomchek and Dunn, 2007
) with prevalence estimates ranging from 30 to 100% of respective study participants (Dawson and Watling, 2000
). Following a meta-analysis of 14 relevant studies, Ben-Sasson et al. (2008
) concluded that “under-responsivity,” delayed or muted response to a stimuli, was reported more by parents of children with ASD than either “over-responsivity” or “seeking” out of stimuli. Several recent reports point to the processing deficiencies of visual, auditory, tactile and proprioceptive stimuli in individuals with autism (Jasmin et al., 2008
; Orekhova et al., 2012
; Paton et al., 2012
). These hypo-responses may actually be the result of increased sensitivity to stimuli rather than the opposite (Rinaldi et al., 2008
). Through various work on a valproic acid rat model of autism, Markram et al. (2007
) suggests that both increased response to stimuli and increased plasticity of neuronal circuits may explain altered responses observed in ASD. While it could be argued whether these sensory processing deficits are a core feature of ASD or a co-morbidity, it is apparent that they are present in a large percentage of individuals with ASD and they impact communication, social interaction, and movement qualities.
Propioceptive deficits in individuals with ASD have received less inquiry than other sensory types, although proper joint and limb positioning is critical for movement precision. Afferent proprioceptive feedback is primarily afforded from golgi tendon organs, muscle spindles, joint receptors, and skin receptors. This feedback is critical during all forms of human location (e.g., running, walking, hopping) as the leg acts as a tuned spring that can store and return a certain percentage of energy (Farley et al., 1991
; Ferris and Farley, 1997
). During landing the leg spring is compressed storing energy and during propulsion the leg spring rebounds as the joints (hip, knee, ankle) extend. Leg spring stiffness is actively controlled as both a factor of locomotion speed and ground surface compliance in order to minimize overall energetic cost. Propioceptive feedback is necessary to essentially “tune” leg spring stiffness and maximize the amount of returned energy. When children with autism learn a novel task, there is a stronger association between proprioceptive feedback and self-generated motor commands than seen in typically developing children (Haswell et al., 2009
). Haswell et al. (2009
) speculate that overexpression of cortical connections between the somatosensory cortex and primary motor cortex may explain the increased reliance on proprioceptive feedback in their generalized motor internal model. Altered proprioceptive feedback has also been cited as a potential cause of motor dyspraxia observed in individuals with Asperger syndrome (Weimer et al., 2001
In contrast to these findings in Asperger syndrome, Fuentes et al. (2011
) recently showed children with ASD displayed motor impairment without any deficits in proprioception during a simple upper extremity elbow flexion-extension task. These are compelling results because they may indicate that proprioceptor sensors are neither hyper- or hypo-sensitive in individuals with ASD and it is the rather the integration of proprioceptive information with other sensory inputs (e.g., visual, auditory, vestibular-proprioceptive information) that may be impaired. High functioning individuals with autism have previously demonstrated a delayed motor anticipation response and an inability to decrease reaction time when presented with a visual cue during a button pressing task (Rinehart et al., 2001
). This increased temporal processing seems to be exacerbated in individuals with ASD during conditions of multisensory input (Kwakye et al., 2011
Synchronizing motor output with an auditory cue, sensorimotor synchronization, has been studied extensively via a finger-tapping model (e.g., Kelso, 1984
; Ivry and Keele, 1989
; Sheridan and McAuley, 1997
) but whole body rhythmicity has received much less attention (Rousanoglou and Boudolos, 2006
). Timing of rhythmic movement has been explained via a (1) two-stage timing model (Wing and Kristofferson, 1973
) and a (2) dynamic system model (Schöner, 2002
). Utilizing the two-stage model of synchronization, Ivry and Keele (1989
) discovered that individuals with cerebellar lesions had disruptions of their internal clock variance but not motor error variance during an auditory-cued finger tapping task. Similarly, Sheridan and McAuley (1997
) reported that ASD children were less accurate and more variable with finger tapping precision than control groups. Although the two-stage timing model has been used to explain timing and motor errors during finger tapping, Rousanoglou and Boudolos (2006
) found that timing control during an auditory-cued two-legged hopping in place task could be explained via a dynamic systems model. The authors speculate that alteration of joint stiffness may modify the rate of ground reaction force development (RFD) during the landing phase and that RFD may serve as a timing regulator. No previous work has examined whole body sensorimotor synchronization in ASD.
It is also noteworthy that the most extreme differences or disorders of movement regulation and/or regulation of proprioceptive feedback may correlate with the “severity” of ASD. Donnellan et al. (2010
) present evidence that disorders of sensory processes and movement are endemic to all forms of ASD. However, the evidence that they present raises the inquiry of whether individuals who have the most compromised forms of “self advocacy” such as significant expressive language challenges also present with more profound differences in a range of sensory-movement anomalies (Hill and Leary, 1993
; Donnellan et al., 2006
). Furthermore, there remains the need to differentiate the developmental presentations across the range of individuals who have differing forms of an ASD diagnosis.
Therefore, the purpose of this study was to investigate whether individuals with ASD with expressive language impairments (ELI-ASD) could modify their motor control strategy during a multi-joint gross motor activity (two-legged hopping in place) to match an auditory cue (temporal synchrony). It was hypothesized that:
H(1) The individuals with ELI-ASD would be able to successfully complete a two-legged hopping in place task at a self-selected cadence.
H(2) The individuals with ELI-ASD population would not match their hopping cadence to an external auditory cue while all control participants would be within 5% of the cue.
H(3) There would be a range of responses within the ELI-ASD population.
The results of this study may potentially further our understanding of sensory processing deficits in this population and provide a basis for a quantitative movement assessment screening tool that could be used to evaluate intervention efficacies and better classify individuals with ASD.