Biomedical subjects

Thomas A Stoffregen

Publications and source records attributed to Thomas A Stoffregen.

4 recordsLinked to original sources

PubMed2004

Task-specific stabilization of postural coordination during stance on a beam.

Surfaces shorter in extent than the feet elicit multi-joint coordination that differs from what is elicited by stance on extensive surfaces. This well-known effect arises from the mechanics of the actor-environment interaction. Multi-joint control of stance is also known to be influenced by non-mechanical aspects of a situation, including participants' task or intention. Intentional constraints do not originate in mechanics, and for this reason one might suppose that constraints imposed by mechanics would dominate constraints imposed by intentions, when the two were in conflict. We evaluated this hypothesis by varying participants' supra-postural task during stance on a short surface. While standing on a 10-cm wide beam, participants were exposed to optic flow generated by fore-aft oscillations of a moving room. Participants faced a target attached to the front wall of the moving room and were asked either to look at the target (with no instruction to move) or intentionally to track it with their head (i.e., to keep the target-head distance constant). Within trials, we varied the frequency of room (and target) motion, from 0.15 to 0.75 Hz, in steps of 0.05 Hz. In both conditions, ankle and hip rotations exhibited anti-phase coordination, but behavior was not identical across conditions. Coupling between motion of the room and the head was stronger for the tracking task than for the looking task, and the stability of ankle-hip coordination was greater during tracking than during looking. These results indicate that the influence of support surface mechanics did not eliminate the influence of the supra-postural task. Environment-based and task-based constraints interacted in determining the coordination of hips and ankles during stance.

Adaptation, Physiological↗

PubMed2002

Postural coordination in looking and tracking tasks.

Participants stood in a moving room and looked at a target that was attached to the front wall of the room. They were instructed either to look at the target or to track it, that is, to move so as to maintain a constant distance between the target and their head. Previous research (e.g. Bardy, Oullier, Bootsma, & Stoffregen, Journal of Experimental Psychology: Human Perception and Performance, 2002) has documented stable modes of coordination of the hip and ankle joints that emerge during the tracking task. In the present study our main goal was to determine the effects of task variation (tracking versus looking) on these postural coordination modes. Within trials, we varied the frequency of room motion between 0.10 and 0.75 Hz. The results revealed that in both the tracking and looking tasks, posture was characterized by the emergence of in-phase and anti-phase modes, although the modes were more prominent in the tracking task. For both tasks the coordination mode adopted depended on the frequency of motion of the moving room. Coupling between motion of the room and motion of the head was stronger in the tracking task than in the looking task. Overall, the dynamics of hip-ankle coordination were qualitatively similar during the looking and tracking tasks. This similarity has consequences for the development of a general theory of the visual regulation of stance.

Adolescent↗

PubMed2002

Visually induced motion sickness predicted by postural instability.

We investigated whether postural instability can predict motion sickness and studied relations among instability, motion sickness, and vection. Nine men and 4 women (mean age = 19.85 years) were exposed, while standing, to an optical simulation of body sway. Head motion was recorded using a magnetic tracking system. Postural instabilities were observed prior to the onset of motion sickness. Vection was reported by most participants, including all who became ill. A discriminant analysis revealed that parameters of postural motion accurately predicted motion sickness. The results confirm that postural instability precedes motion sickness and suggest that measures of postural motion may serve as reliable predictors of motion sickness. Potential applications of this research include the development of on-line diagnostic tools that will allow for the prevention of motion sickness in operational and training settings.

Adolescent↗

PubMed2002

Dynamics of human postural transitions.

In the present study, the authors examined transitions between postural coordination modes involved in human stance. The analysis was motivated by dynamical theories of pattern formation, in which coordination modes and transitions between modes are emergent, self-organized properties of the dynamics of animal-environment systems. In 2 experiments, standing participants tracked a moving target with the head. Results are consistent with the hypothesis that changes in body coordination follow typical nonequilibrium phase transitions, exhibiting multistability, bifurcation, critical fluctuations, hysteresis, and critical slowing down. The findings suggest that posture may be organized in terms of dynamical principles and favor the existence of general and common principles governing pattern formation and flexibility in complex systems.

Adult↗