Does Proprioception Influence Human Spatial Cognition? A Study on Individuals With Massive Deafferentation.

When navigating in a spatial environment or when hearing its description, we can develop a mental model which may be represented in the central nervous system in different coordinate systems such as an egocentric or allocentric reference frame. The way in which sensory experience influences the preferred reference frame has been studied with a particular interest for the role of vision. The present study investigated the influence of proprioception on human spatial cognition. To do so, we compared the abilities to form spatial models of two rare participants chronically deprived of proprioception (GL and IW) and healthy control participants. Participants listened to verbal descriptions of a spatial environment, and their ability to form and use a mental model was assessed with a distance-comparison task and a free-recall task. Given that the loss of proprioception has been suggested to specifically impair the egocentric reference frame, the deafferented individuals were expected to perform worse than controls when the spatial environment was described in an egocentric reference frame. Results revealed that in both tasks, one deafferented individual (GL) made more errors than controls while the other (IW) made less errors. On average, both GL and IW were slower to respond than controls, and reaction time was more variable for IW. Additionally, we found that GL but not IW was impaired compared to controls in visuo-spatial imagery, which was assessed with the Minnesota Paper Form Board Test. Overall, the main finding of this study is that proprioception can influence the time necessary to use spatial representations while other factors such as visuo-spatial abilities can influence the capacity to form accurate spatial representations.

Spatial Cues Provided by Sound Improve Postural Stabilization: Evidence of a Spatial Auditory Map?

It has long been suggested that sound plays a role in the postural control process. Few studies however have explored sound and posture interactions. The present paper focuses on the specific impact of audition on posture, seeking to determine the attributes of sound that may be useful for postural purposes. We investigated the postural sway of young, healthy blindfolded subjects in two experiments involving different static auditory environments. In the first experiment, we compared effect on sway in a simple environment built from three static sound sources in two different rooms: a normal vs. an anechoic room. In the second experiment, the same auditory environment was enriched in various ways, including the ambisonics synthesis of a immersive environment, and subjects stood on two different surfaces: a foam vs. a normal surface. The results of both experiments suggest that the spatial cues provided by sound can be used to improve postural stability. The richer the auditory environment, the better this stabilization. We interpret these results by invoking the "spatial hearing map" theory: listeners build their own mental representation of their surrounding environment, which provides them with spatial landmarks that help them to better stabilize.

Reaching nearby sources: comparison between real and virtual sound and visual targets.

Sound localization studies over the past century have predominantly been concerned with directional accuracy for far-field sources. Few studies have examined the condition of near-field sources and distance perception. The current study concerns localization and pointing accuracy by examining source positions in the peripersonal space, specifically those associated with a typical tabletop surface. Accuracy is studied with respect to the reporting hand (dominant or secondary) for auditory sources. Results show no effect on the reporting hand with azimuthal errors increasing equally for the most extreme source positions. Distance errors show a consistent compression toward the center of the reporting area. A second evaluation is carried out comparing auditory and visual stimuli to examine any bias in reporting protocol or biomechanical difficulties. No common bias error was observed between auditory and visual stimuli indicating that reporting errors were not due to biomechanical limitations in the pointing task. A final evaluation compares real auditory sources and anechoic condition virtual sources created using binaural rendering. Results showed increased azimuthal errors, with virtual source positions being consistently overestimated to more lateral positions, while no significant distance perception was observed, indicating a deficiency in the binaural rendering condition relative to the real stimuli situation. Various potential reasons for this discrepancy are discussed with several proposals for improving distance perception in peripersonal virtual environments.

The influence of horizontally rotating sound on standing balance.

Postural control is known to be the result of the integration and processing of various sensory inputs by the central nervous system. Among the various afferent inputs, the role of auditory information in postural regulation has been addressed in relatively few studies, which led to conflicting results. The purpose of the present study was to investigate the influence of a rotating auditory stimulus, delivered by an immersive 3D sound spatialization system, on the standing posture of young subjects. The postural sway of 20 upright, blindfolded subjects was recorded using a force platform. Use of various sound source rotation velocities followed by sudden immobilization of the sound was compared with two control conditions: no sound and a stationary sound source. The experiment showed that subjects reduced their body sway amplitude and velocity in the presence of rotating sound compared with the control conditions. The faster the sound source was rotating, the greater the reduction in subject body sway. Moreover, disruption of subject postural regulation was observed as soon as the sound source was immobilized. These results suggest that auditory information cannot be neglected in postural control and that it acts as additional information influencing postural regulation.

Rapid head-related transfer function adaptation using a virtual auditory environment.

The paper reports on the ability of people to rapidly adapt in localizing virtual sound sources in both azimuth and elevation when listening to sounds synthesized using non-individualized head-related transfer functions (HRTFs). Participants were placed within an audio-kinesthetic Virtual Auditory Environment (VAE) platform that allows association of the physical position of a virtual sound source with an alternate set of acoustic spectral cues through the use of a tracked physical ball manipulated by the subject. This set-up offers a natural perception-action coupling, which is not limited to the visual field of view. The experiment consisted of three sessions: an initial localization test to evaluate participants' performance, an adaptation session, and a subsequent localization test. A reference control group was included using individual measured HRTFs. Results show significant improvement in localization performance. Relative to the control group, participants using non-individual HRTFs reduced localization errors in elevation by 10° with three sessions of 12 min. No significant improvement was found for azimuthal errors or for single session adaptation.

Perceptually based head-related transfer function database optimization.

In the context of binaural audio rendering, choosing the best head-related transfer function (HRTF) for an individual from large databases poses several problems. This study proposes a method to reduce the size of a given HRTF database. Participants, 45 in total, were asked to rate the quality of binaural synthesis for 46 HRTFs. The lack of reciprocity in the ratings was noted. Results were used to create a perceptually optimized HRTF subset which satisfied all participants' judgments. The subset was validated using localization tests on a separate group of subjects with results showing reduced errors when subjects were given their best choice, rather than their worst choice HRTF.