Allocentric Constraints Research Articles

The effects of feedback format, and egocentric & allocentric relative phase on coordination stability

The stability of coordinated rhythmic movement is primarily affected by the required mean relative phase. In general, symmetrical coordination is more stable than asymmetrical coordination; however, there are two ways to define relative phase and the associated symmetries. The first is in an egocentric frame of reference, with symmetry defined relative to the sagittal plane down the midline of the body. The second is in an allocentric frame of reference, with symmetry defined in terms of the relative direction of motion. Experiments designed to separate these constraints have shown that both egocentric and allocentric constraints contribute to overall coordination stability, with the former typically showing larger effects. However, separating these constraints has meant comparing movements made either in different planes of motion, or by limbs in different postures. In addition, allocentric information about the coordination is either in the form of the actual limb motion, or a transformed, Lissajous feedback display. These factors limit both the comparisons that can be made and the interpretations of these comparisons. The current study examined the effects of egocentric relative phase, allocentric relative phase, and allocentric feedback format on coordination stability in a single task. We found that while all three independently contributed to stability, the egocentric constraint dominated. This supports previous work. We examine the evidence underpinning theoretical explanations for the egocentric constraint, and describe how it may reflect the haptic perception of relative phase.

Handing a tool to someone can take more time than using it

Jax and Buxbaum [Jax and Buxbaum (2010). Response interference between functional and structural actions linked to the same familiar object. Cognition, 115, 350–355] demonstrated that grasp-to-transport actions (handing an object to someone, i.e., a receiver) are initiated more quickly than grasp-to-use actions. A possible interpretation of these findings is that grasp-to-transport actions do not require activation of long-term representations. In Jax and Buxbaum’s study, participants positioned their hand on the object as they would to transport/use it in a conventional way. So, movement planning was based only on egocentric relationships (individual-object) and not on allocentric relationships (object–object or object-“receiver”). It is likely that participants may not have activated long-term social representations about how to hand an object to someone in the transport task. In Experiment 1, we replicated J&B’s results by asking participants to position their hand on familiar tools as they would to hand them to someone (grasp-to-transport)/use them in a non-conventional way (i.e., to hit a ball, grasp-to-use). In Experiment 2, participants had to actually perform the actions. We found the opposite pattern in that grasp-to-use actions were initiated more quickly than grasp-to-transport actions. These findings indicate that the modulation of allocentric constraints might induce activation of long-term representations in transport actions. This suggests that, under certain circumstances, long-term representations might be necessary not only for use actions but also for transport actions.

Coordinative constraints in bimanual tool use

This study investigates coordinative constraints when participants execute discrete bimanual tool use actions. Participants moved two levers to targets that were either presented near the proximal parts of the levers or near the distal tips of the levers. In the first case, the tool transformation (i.e. the relationship between hand movement direction and target direction) was compatible, whereas in the second case, it was incompatible. We hypothesized that an egocentric constraint (i.e. a preference for moving the hands and tools in a mirror-symmetrical fashion) would be dominant when targets are presented near the proximal parts of the levers because in this situation, movements can be coded in terms of body-related coordinates. Furthermore, an allocentric constraint (i.e. a preference to move the hands in the same (parallel) direction in extrinsic space) was expected to be dominant when one of the targets or both are presented near the distal parts of the levers because in this condition, movements have to be coded in an external reference frame. The results show that when both targets are presented near the proximal parts of the levers, participants are faster and produce less errors with mirror-symmetrical when compared to parallel movements. Furthermore, the RT mirror-symmetry advantage is eliminated, when both targets are presented near the distal parts of the levers, and it is reversed, when the target for one lever is presented near its distal part and the target for the other lever is presented near its proximal part. These results show that the dominance of egocentric and allocentric coordinative constraints in bimanual tool use depends on whether movements are coded in terms of body-related coordinates or in an external reference frame.

The role of directional compatibility in assembling coordination patterns involving the upper and lower limb girdles and the head

The role of directional compatibility was investigated during the production of in-phase and anti-phase coordination patterns involving the four limbs as well as the head. Our first aim was to compare the quality of interlimb coordination between concordant and discordant coordination patterns across girdles at different cycling frequencies. Concordant implied adoption of either the in-phase or anti-phase coordination mode across both girdles whereas discordant implied a combination of both modes. The second aim was to study the effect of periodic head movements upon the assembling of a coordinative synergy among the limbs. Findings revealed that concordant coordination modes were produced with higher accuracy and consistency than discordant coordination modes and this effect was more distinct at higher cycling frequencies. Inclusion of head movements was found to destabilize in-phase coordination but stabilize anti-phase coordination patterns, particularly during discordant conditions at higher cycling frequencies. This observation contrasts with previous findings in which anti-phase modes have invariably been shown to be more vulnerable to experimental perturbations than in-phase modes. The findings are discussed within the context of the coalition of egocentric and allocentric constraints during multilimb coordination and the role of direction as an organizing principle in movement control.

Head movements destabilize cyclical in-phase but not anti-phase homologous limb coordination in humans

The present study addressed the role of head movements in the coordination of the homologous upper or lower limbs in supine normal subjects. Consistent with previous research, in-phase mirror symmetrical movements were performed more accurately and consistently than anti-phase movements. However, inclusion of head movements destabilized in-phase but not anti-phase homologous limb coordination, in contrast to previous work demonstrating a higher vulnerability of anti-phase than in-phase coordination to various experimental perturbations. It was observed that the head moved in the same direction as the limbs during anti- but not during in-phase coordination. Furthermore, the interlimb patterns also affected the head rotations that were lower in spatiotemporal consistency and less consistently coupled with the limbs during in-phase than during anti-phase coordination. These findings provide new insights into the coalition of egocentric and allocentric constraints during interlimb coordination.

Exploring interlimb constraints during bimanual graphic performance: effects of muscle grouping and direction

Past studies on bimanual coordination have revealed a general preference to move the limbs in a symmetrical fashion, also denoted as the in-phase mode. Its counterpart, the asymmetrical or anti-phase mode, is performed with lower degrees of accuracy and stability. This ubiquitous tendency to activate the homologous muscle groups is referred to as the muscle grouping constraint (egocentric constraint). The present study confirmed the generalizability of this constraint across various coordination patterns, performed in the horizontal plane. In addition, evidence was generated that movement direction in extrinsic space also constrains bimanual coordination (allocentric constraint). Overall, the present observations suggest that direction is an important movement parameter that is encoded in the central nervous system and that is subject to interactions between the neural specifications of both limbs.

Egocentric and Allocentric Constraints in the Expression of Patterns of Interlimb Coordination

Tasks that are easy when performed in isolation become difficult when performed simultaneously in the upper and/or lower limbs. This observation points to basic CNS constraints in the organization of patterns of interlimb coordination. The present studies provide evidence for the existence of two basic coordinative constraints whose effects may be additive under certain conditions. On one hand, the egocentric constraint denotes a general preference for moving the limbs toward or away from the longitudinal axis of the body in a symmetrical fashion and is of primary importance during the coordination of homologous limbs. On the other hand, the allocentric constraint refers to a general preference to move the limbs in the same direction in extrinsic space and pertains to the coordination of nonhomologous limbs (eg., various combinations of the upper and lower limbs). In the present context, constraints are considered as expressions of basic features of CNS operation that give way to preferred coordination patterns to which the system is naturally drawn or biased. The identification and description of these constraints is considered of critical importance to obtain a better understanding of the control of coordination patterns.