Manuel Varlet

Social postural coordination.

The goal of the current study was to investigate whether a visual coupling between two people can produce spontaneous interpersonal postural coordination and change their intrapersonal postural coordination involved in the control of stance. We examined the front-to-back head displacements of participants and the angular motion of their hip and ankle during a visual tracking task performed alone and paired. Our results showed that visually paired participants exhibited spontaneous coordination between the movements of their head, hip, and ankle. Moreover, the visual coupling modified the spontaneous intrapersonal ankle-hip coordination dynamics of participants and their performance during visual tracking. Generally, our findings demonstrated reciprocal relations between intrapersonal and interpersonal coordination during social interaction.

Getting Your Sea Legs

Sea travel mandates changes in the control of the body. The process by which we adapt bodily control to life at sea is known as getting ones sea legs. We conducted the first experimental study of bodily control as maritime novices adapted to motion of a ship at sea. We evaluated postural activity (stance width, stance angle, and the kinematics of body sway) before and during a sea voyage. In addition, we evaluated the role of the visible horizon in the control of body sway. Finally, we related data on postural activity to two subjective experiences that are associated with sea travel; seasickness, and mal de debarquement. Our results revealed rapid changes in postural activity among novices at sea. Before the beginning of the voyage, the temporal dynamics of body sway differed among participants as a function of their (subsequent) severity of seasickness. Body sway measured at sea differed among participants as a function of their (subsequent) experience of mal de debarquement. We discuss implications of these results for general theories of the perception and control of bodily orientation, for the etiology of motion sickness, and for general phenomena of perceptual-motor adaptation and learning.

Effects of movement stability and congruency on the emergence of spontaneous interpersonal coordination

The current project evaluated the relationship between the stability of intrapersonal coordination and the emergence of spontaneous interpersonal coordination. Participants were organized into pairs, and each participant was instructed to produce either an inphase or antiphase pattern of intrapersonal bimanual coordination using two hand-held pendulums, while simultaneously performing an interpersonal puzzle task. At issue was whether the emergence and stability of spontaneous interpersonal rhythmic coordination is influenced by (“Experiment 1”) the stability of the intrapersonal coordination patterns produced by co-actors and (“Experiment 2”) the congruency of the intrapersonal coordination patterns produced by co-actors. The stability of intrapersonal movement coordination did not affect the emergence of spontaneous interpersonal coordination. The degree of interpersonal coordination observed was similar when both participants in a pair produced either inphase or antiphase patterns of intrapersonal bimanual coordination. Moreover, the congruency of the intrapersonal coordination patterns only slightly affected the emergence of interpersonal coordination, with only marginally lower inphase interpersonal entrainment when participants produced incongruent patterns of intrapersonal coordination (e.g., inphase–antiphase). Interestingly, movement observation and the emergence of interpersonal coordination did not affect the stability of intrapersonal bimanual coordination. The results suggest that interlimb rhythmic bimanual coordination reflects a single intrapersonal perceptual-motor synergy and that these bimanual synergies (not individual limbs) are what become spontaneously entrained interpersonally.

Coordination dynamics in a socially situated nervous system

Traditional theories of cognitive science have typically accounted for the organization of human behavior by detailing requisite computational/representational functions and identifying neurological mechanisms that might perform these functions. Put simply, such approaches hold that neural activity causes behavior. This same general framework has been extended to accounts of human social behavior via concepts such as “common-coding” and “co-representation” and much recent neurological research has been devoted to brain structures that might execute these social-cognitive functions. Although these neural processes are unquestionably involved in the organization and control of human social interactions, there is good reason to question whether they should be accorded explanatory primacy. Alternatively, we propose that a full appreciation of the role of neural processes in social interactions requires appropriately situating them in their context of embodied-embedded constraints. To this end, we introduce concepts from dynamical systems theory and review research demonstrating that the organization of human behavior, including social behavior, can be accounted for in terms of self-organizing processes and lawful dynamics of animal-environment systems. Ultimately, we hope that these alternative concepts can complement the recent advances in cognitive neuroscience and thereby provide opportunities to develop a complete and coherent account of human social interaction.

Influence of stimulus amplitude on unintended visuomotor entrainment

Rhythmic limb movements have been shown to spontaneously coordinate with rhythmic environmental stimuli. Previous research has demonstrated how such entrainment depends on the difference between the movement periods of the limb and the stimulus, and on the degree to which the actor visually tracks the stimulus. Here we present an experiment that investigated how stimulus amplitude influences unintended visuomotor entrainment. Participants performed rhythmic forearm movements while visually tracking an oscillating stimulus. The amplitude and period of stimulus motion were manipulated. Larger stimulus amplitudes resulted in stronger entrainment irrespective of how participants visually tracked the movements of the stimulus. Visual tracking, however, did result in increased entrainment for large, but not small, stimulus amplitudes. Collectively, the results indicate that the movement amplitude of environmental stimuli plays a significant role in the emergence of unintended visuomotor entrainment.

Computation of continuous relative phase and modulation of frequency of human movement

Continuous relative phase measures have been used to quantify the coordination between different body segments in several activities. Our aim in this study was to investigate how the methods traditionally used to compute the continuous phase of human rhythmic movement are affected by modulations of frequency. We compared the continuous phase computed method with the traditional method derived from the position-velocity phase plane and with the Hilbert Transform. The methods were tested using sinusoidal signals with a modulation of frequency between or within cycles. Our results showed that the continuous phase computed with the first method results in oscillations in the phase time-series not expected for a sinusoidal signal and that the continuous phase is overestimated with the Hilbert Transform. We proposed a new method that produces a correct estimation of continuous phase by using half-cycle estimations of frequency to normalize the phase planes prior to calculating phase angles. The findings of the current study have important implications for computing continuous relative phase when investigating human movement coordination.

Difficulty leading interpersonal coordination: towards an embodied signature of social anxiety disorder

Defined by a persistent fear of embarrassment or negative evaluation while engaged in social interaction or public performance, social anxiety disorder (SAD) is one of the most common psychiatric syndromes. Previous research has made a considerable effort to better understand and assess this mental disorder. However, little attention has been paid to social motor behavior of patients with SAD despite its crucial importance in daily social interactions. Previous research has shown that the coordination of arm, head or postural movements of interacting people can reflect their mental states or feelings such as social connectedness and social motives, suggesting that interpersonal movement coordination may be impaired in patients suffering from SAD. The current study was specifically aimed at determining whether SAD affects the dynamics of social motor coordination. We compared the unintentional and intentional rhythmic coordination of a SAD group (19 patients paired with control participants) with the rhythmic coordination of a control group (19 control pairs) in an interpersonal pendulum coordination task. The results demonstrated that unintentional social motor coordination was preserved with SAD while intentional coordination was impaired. More specifically, intentional coordination became impaired when patients with SAD had to lead the coordination as indicated by poorer (i.e., more variable) coordination. These differences between intentional and unintentional coordination as well as between follower and leader roles reveal an impaired coordination dynamics that is specific to SAD, and thus, opens promising research directions to better understand, assess and treat this mental disorder.

Predicting the biological variability of environmental rhythms: Weak or strong anticipation for sensorimotor synchronization?

The internal processes involved in synchronizing our movements with environmental stimuli have traditionally been addressed using regular metronomic sequences. Regarding real-life environments, however, biological rhythms are known to have intrinsic variability, ubiquitously characterized as fractal long-range correlations. In our research we thus investigate to what extent the synchronization processes drawn from regular metronome paradigms can be generalized to other (biologically) variable rhythms. Participants performed synchronized finger tapping under five conditions of long-range and/or short-range correlated, randomly variable, and regular auditory sequences. Combining experimental data analysis and numerical simulation, we found that synchronizing with biologically variable rhythms involves the same internal processes as with other variable rhythms (whether totally random or comprising lawful regularities), but different from those involved with a regular metronome. This challenges both the generalizability of conclusions drawn from regular-metronome paradigms, and recent research assuming that biologically variable rhythms may trigger specific strong anticipatory processes to achieve synchronization.

Social motor coordination in unaffected relatives of schizophrenia patients: a potential intermediate phenotype.

Intermediate endophenotypes emerge as an important concept in the study of schizophrenia. Although research on phenotypes mainly investigated cognitive, metabolic or neurophysiological markers so far, some authors also examined the motor behavior anomalies as a potential trait-marker of the disease. However, no research has investigated social motor coordination despite the possible importance of its anomalies in schizophrenia. The aim of this study was thus to determine whether coordination modifications previously demonstrated in schizophrenia are trait-markers that might be associated with the risk for this pathology. Interpersonal motor coordination in 27 unaffected first-degree relatives of schizophrenia patients and 27 healthy controls was assessed using a hand-held pendulum task to examine the presence of interpersonal coordination impairments in individuals at risk for the disorder. Measures of neurologic soft signs, clinical variables and neurocognitive functions were collected to assess the cognitive and clinical correlates of social coordination impairments in at-risk relatives. After controlling for potential confounding variables, unaffected relatives of schizophrenia patients had impaired intentional interpersonal coordination compared to healthy controls while unintentional interpersonal coordination was preserved. More specifically, in intentional coordination, the unaffected relatives of schizophrenia patients exhibited coordination patterns that had greater variability and in which relatives did not lead the coordination. These results show that unaffected relatives of schizophrenia patients, like the patients themselves, also present deficits in intentional interpersonal coordination. For the first time, these results suggest that intentional interpersonal coordination impairments might be a potential motor intermediate endophenotype of schizophrenia opening new perspectives for early diagnosis.

Influence of stimulus velocity profile on rhythmic visuomotor coordination.

Every day, we visually coordinate our movements with environmental rhythms. Despite its ubiquity, it largely remains unclear why certain visual rhythms or stimuli facilitate such visuomotor coordination. The goal of the current study was to investigate whether the velocity profile of a rhythmic stimulus modulated the emergence and stability of this coordination. We examined both intended (Experiment 1) and unintended or spontaneous coordination (Experiment 2) between the rhythmic limb movements of participants and stimuli exhibiting different velocity profiles. Specifically, the stimuli oscillated with either a sinusoidal (harmonic), nonlinear Rayleigh, or nonlinear Van der Pol velocity profile, all of which are typical of human or biological rhythmic movement. The results demonstrated that the dynamics of both intended and unintended visuomotor coordination were modulated by the stimulus velocity profile, and that the Rayleigh velocity profile facilitated the coordination, suggesting a crucial role of the slowness to the endpoints or turning points of the stimulus trajectory for stable coordination. More generally, these findings open promising research directions to better understand and improve coordination with artificial agents and people with social deficits.