Age and the Egocentric Constraint on Coordination Stability: An Exploratory Report

The stability of coordinated rhythmic movements is primarily affected by the target relative phase. Relative phase can be identified in each of two frames of reference (an external, allocentric frame and a body-centred, egocentric frame) and both constrain stability. In the allocentric frame, coordinations that involve isodirectional movement (0° mean relative phase) are more stable than those that do not. In the egocentric frame, coordinations that involve simultaneous use of homologous muscles (in-phase) are more stable than those that do not. The origin of the allocentric constraint is the visual perception of relative phase. The origin of this egocentric frame of reference is still unclear, although it is typically discussed in terms of neural crosstalk. Pickavance, Azmoodeh & Wilson (2018) proposed that the egocentric constraint is also perceptual, based in the haptic perception of relative phase. As an initial step in pursuing this hypothesis, this exploratory report examines some data from two recent studies on the effect of ageing on performing and learning coordinated rhythmic movements. We show that participants in their 20s show a strong egocentric effect in their coordination production, while this disappears in participants in their 60s. Participants in their 50s show an intermediate effect. We propose that a perceptual hypothesis is the best explanation of this age-related change, and lay out how to pursue hypothesis-driven tests in the future.

Virtual/Real Transfer in a Large-Scale Environment: Impact of Active Navigation as a Function of the Viewpoint Displacement Effect and Recall Tasks

The purpose of this study was to examine the effect of navigation mode (passive versus active) on the virtual/real transfer of spatial learning, according to viewpoint displacement (ground: 1 m 75 versus aerial: 4 m) and as a function of the recall tasks used. We hypothesize that active navigation during learning can enhance performances when route strategy is favored by egocentric match between learning (ground-level viewpoint) and recall (egocentric frame-based tasks). Sixty-four subjects (32 men and 32 women) participated in the experiment. Spatial learning consisted of route learning in a virtual district (four conditions: passive/ground, passive/aerial, active/ground, or active/aerial), evaluated by three tasks:wayfinding,sketch-mapping,andpicture-sorting. In thewayfinding task, subjects who were assigned the ground-level viewpoint in the virtual environment (VE) performed better than those with the aerial-level viewpoint, especially in combination with active navigation. In thesketch-mapping task, aerial-level learning in the VE resulted in better performance than the ground-level condition, while active navigation was only beneficial in the ground-level condition. The best performance in thepicture-sorting taskwas obtained with the ground-level viewpoint, especially with active navigation. This study confirmed the expected results that the benefit of active navigation was linked with egocentric frame-based situations.

Effects of head orientation and lateral body tilt on egocentric coding: Cognitive and sensory-motor accuracy

A major issue in motor control studies is to determine whether and how we use spatial frames of reference to organize our spatially oriented behaviors. In previous experiments [2,16] we showed that simulated body tilt during off-axis rotation affected the performance in verbal localization and manual pointing tasks. It was hypothesized that the observed alterations were at least partly due to a change in the orientation of the egocentric frame of reference, which was indeed centered on the body but aligned with the gravitational vector. The present experiments were designed to test this hypothesis in a situation where no inertial constraints (except the usual gravitational one) exist and where the orientation of the body longitudinal z-axis was not aligned with the direction of the gravity. Eleven subjects were exposed to real static body tilt and were required to verbally localize (experiment 1) and to point as accurately as possible towards (experiment 2) memorized visual targets, in two conditions, Head-Free and Head-Fixed conditions. Results show that the performance was only affected by real body tilt in the localization task performed when the subject's head was tilted relative to the body. Thus, dissociation between gravity and body longitudinal z-axis alone is not responsible for localization nor for pointing errors. Therefore, the egocentric frame of reference seems independent from the orientation of the gravity with regard to body z-axis as expected from our previous studies. Moreover, the use of spatial referentials appears to be less mandatory than expected for pointing movements (motor task) than for localization task (cognitive task).

Erratum

Anthony Marcel, Christian Dobel, 2005 “Structured perceptual input imposes an egocentric frame of reference—pointing, imagery, and spatial self-consciousness” Perception 34 429 – 451 The last sentence of paragraph 3 on page 443 reads: (iv) “What is the angle between your arms or draw the shape made by your two arms”. It should read: (iv) “What is the angle between your arms? Or draw the shape made by your two arms.” The heading of column 6 of table 1 on page 444 reads: Number/total subjects showing confusion It should read: Number/total number of subjects showing confusion

Structured Perceptual Input Imposes an Egocentric Frame of Reference—Pointing, Imagery, and Spatial Self-Consciousness

Perceptual input imposes and maintains an egocentric frame of reference, which enables orientation. When blindfolded, people tended to mistake the assumed intrinsic axes of symmetry of their immediate environment (a room) for their own egocentric relation to features of the room. When asked to point to the door and window, known to be at mid-points of facing (or adjacent) walls, they pointed with their arms at 180° (or 90°) angles, irrespective of where they thought they were in the room. People did the same when requested to imagine the situation. They justified their responses (inappropriately) by logical necessity or a structural description of the room rather than (appropriately) by relative location of themselves and the reference points. In eight experiments, we explored the effect on this in perception and imagery of: perceptual input (without perceptibility of the target reference points); imaging oneself versus another person; aids to explicit spatial self-consciousness; order of questions about self-location; and the relation of targets to the axes of symmetry of the room. The results indicate that, if one is deprived of structured perceptual input, as well as losing one's bearings, (a) one is likely to lose one's egocentric frame of reference itself, and (b) instead of pointing to reference points, one demonstrates their structural relation by adopting the intrinsic axes of the environment as one's own. This is prevented by providing noninformative perceptual input or by inducing subjects to imagine themselves from the outside, which makes explicit the fact of their being located relative to the world. The role of perceptual contact with a structured world is discussed in relation to sensory deprivation and imagery, appeal is made to Gibson's theory of joint egoreception and exteroception, and the data are related to recent theories of spatial memory and navigation.