Intra-and interpersonal inter]imb coordination of pendulums swung from the wrist was investigated. For both kinds of coordination, the steady state and breakdown of bimanual rhythmic coordination as indexed by the time series of the relative phase angle it were studied under the manipulation of coordination mode, frequency of oscillation, and the difference in the eigenfrequencies (preferred tempos) of the individual oscillating limbs. The properties observed for both intra-and interpersonal coordination were those predicted by a dynamical model of rhythmic coordination that considers the coordinated limbs coupled to be nonlinear oscillators. Using a regression method, the coupling strengths of the coupled system were recovered. As predicted by the dynamical model, the strength of the dynamic was generally greater for the in-phase than the anti-phase mode and decreased with increasing frequency. Further, the strength of the interpersonal interlimb coupling was weaker than that of intrapersonal interlimb coupling.Much research over the past decade has demonstrated that stable patterns of interlimb coordination and their dissolution can be modeled by assuming that the nervous system and concomitant metabolic machinery manifest dynamical processes of self-organization (Haken, Kelso, & Bunz, 1985;Kelso, 1990;Kugler, Kelso, & Turvey, 1980;Kugler & Turvey, 1987;Turvey, 1990). The methodological tactic of this research has been to demonstrate that the patterns of rhythmic coordination observed in single (Feldman, 1980;Kay, Saltzman, & Kelso, 1991) and multilimb (Beek, 1989;Kelso & Jeka, 1992;Schmidt, Shaw, & Turvey, 1993) movements are just those expected if the neuromuscular systems involved are governed by the dynamics of nonlinear oscillators. Interestingly, research has also demonstrated that patterns of coordination similar to those found in withinperson interlimb coordination occur in rhythmic movements optically coordinated across two people (Schmidt, Carello, & Turvey, 1990;Schmidt & Turvey, 1994). These latter findings demonstrate the generality and abstract incorporeal nature of the organizing principles involved in biological rhythmic coordination: The same control processes seem to be at work regardless of whether the coordination involves one nervous system or two or whether the coupling medium is the optic array or neural tissue. In two experiments we further compared the coordination dynamics found in intraand interpersonal interlimb rhythmic movements, particularly the strength of those dynamics and their patterns of coordination breakdown. We did this using a methodology that manipulated the frequency of oscillation and the dynamical similarity (i.e., the preferred frequency or eigenfrequency difference) of the rhythmic units being coordinated. We also present a new method of measuring the strength of the coupled oscillatory dynamic.The research on the dynamics underlying interlimb rhythmic coordination has used the relative phase angle (

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Social interactions typically involve movements of the body that become synchronized over time and both intentional and spontaneous interactional synchrony have been found to be an essential part of successful human interaction. However, our understanding of the importance of temporal dimensions of social motor synchrony in social dysfunction is limited. Here, we used a pendulum coordination paradigm to assess dynamic, process-oriented measures of social motor synchrony in adolescents with and without autism spectrum disorder (ASD). Our data indicate that adolescents with ASD demonstrate less synchronization in both spontaneous and intentional interpersonal coordination. Coupled oscillator modeling suggests that ASD participants assembled a synchronization dynamic with a weaker coupling strength, which corresponds to a lower sensitivity and decreased attention to the movements of the other person, but do not demonstrate evidence of a delay in information transmission. The implication of these findings for isolating an ASD-specific social synchronization deficit that could serve as an objective, bio-behavioral marker is discussed.

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Perception of the extents of occluded rods was examined under conditions in which a rod was held as steadily as possible. A given rod was held horizontally, on one side of its center of mass, with one upward ((.') and one downward (D) force. Extent was perceived when D and U were distributed over the surfaces of 1 hand. 2 hands, and a hand and a knee and if only D or only U was provided anatomically, the other being provided by an environmental support. Increasing the distance between D and U decreased perceived extent when both contact points were anatomical and when only I was anatomical. The first moment of the mass distribution, a constant, affected perceived extent more than gravitational torque, a variable. Rods of different lengths but of the same first moment were not distinguished. Results are discussed in terms of functionally equivalent, haptic perceptual instruments and the detection of invariants.

Children with Autism Spectrum Disorder (ASD) suffer from numerous impairments in social interaction that affect both their mental and bodily coordination with others. We explored here whether interpersonal motor coordination may be an important key for understanding the profound social problems of children with ASD. We employed a set of experimental techniques to evaluate not only traditional cognitive measures of social competence but also the dynamical structure of social coordination by using dynamical measures of social motor coordination and analyzing the time series records of behavior. Preliminary findings suggest that children with ASD were equivalent to typically developing children on many social performance outcome measures. However, significant relationships were found between cognitive social measures (e.g., intentionality) and dynamical social motor measures. In addition, we found that more perceptually-based measures of social coordination were not associated with social motor coordination. These findings suggest that social coordination may not be a unitary construct and point to the promise of this multi-method and process-oriented approach to analyzing social coordination as an important pathway for understanding ASD-specific social deficits.