Abstract
Spatial memory is mainly studied through the visual sensory modality: navigation tasks in humans rarely integrate dynamic and spatial auditory information. In order to study how a spatial scene can be memorized on the basis of auditory and idiothetic cues only, we constructed an auditory equivalent of the Morris water maze, a task widely used to assess spatial learning and memory in rodents. Participants were equipped with wireless headphones, which delivered a soundscape updated in real time according to their movements in 3D space. A wireless tracking system (video infrared with passive markers) was used to send the coordinates of the subject's head to the sound rendering system. The rendering system used advanced HRTF-based synthesis of directional cues and room acoustic simulation for the auralization of a realistic acoustic environment. Participants were guided blindfolded in an experimental room. Their task was to explore a delimitated area in order to find a hidden auditory target, i.e., a sound that was only triggered when walking on a precise location of the area. The position of this target could be coded in relationship to auditory landmarks constantly rendered during the exploration of the area. The task was composed of a practice trial, 6 acquisition trials during which they had to memorize the localization of the target, and 4 test trials in which some aspects of the auditory scene were modified. The task ended with a probe trial in which the auditory target was removed. The configuration of searching paths allowed observing how auditory information was coded to memorize the position of the target. They suggested that space can be efficiently coded without visual information in normal sighted subjects. In conclusion, space representation can be based on sensorimotor and auditory cues only, providing another argument in favor of the hypothesis that the brain has access to a modality-invariant representation of external space.
Highlights
We perceive the world around us through multiple senses
Spatial cognition has mainly been studied in experimental situations without auditory information: View-based approaches for spatial memory are the most common
The following three familiar and distinct sound samples were used as constantly active auditory landmarks: a melody played on a piano, a text read by a male voice, and a cicada
Summary
We perceive the world around us through multiple senses. When we explore an environment, we produce idiothetic information through vestibular receptors, muscle and joint receptors, and efference copy of commands that generate movement. As in the water maze, participants are required to find a platform (hidden target) surrounded by a set of landmarks. We asked participants to actively explore this scene in order to learn to locate the target on the basis of cues provided by the auditory-motor loop. It is known that to localize sound requires the integration of multisensory information and the processing of self-generated movements, a stable representation of an auditory source has to be based on acoustic inputs and their relation to motor states (Aytekin et al, 2008). We devised tests to ascertain which aspects of the organization of the landmarks were involved in determining the locus of search and to understand whether the principles of spatial cognition that have been largely developed on the basis of vision hold as general principles independent of the sensory modality or, are completely dependent on the stimulated sensory modality. We expected that the difficulties the participants encountered would be different in function of modifications of the geometrical configuration of the landmarks (like in test 1—Removal and test 2—Rotation), the identity of the landmarks (as in test 3—Switch), or the boundary of the surface layout (as in test 4—Perimeter)
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