The acoustic environment around us often contains multiple sounds: the voices of people speaking nearby, the murmur of a distant conversation, the background noise of a fan or the sound of a television. Our brain manages to unravel this complex acoustic scene thanks to the differences perceived between one sound and another (a male voice or a female voice) and to the capacity to locate each sound in a different position in space. Hearing impairment changes the perception of the acoustic scene, making it difficult or impossible to distinguish sounds. For this reason people with hearing loss feel uncomfortable in noisy environments, and frequently choose to limit their social life. Even though today we have better options than ever before for improving hearing – such as digital hearing aids or cochlear implants – in clinical practice the evaluation of acoustic spatial perception is rare; it is measured using instruments that do not reflect the complexity of the auditory scene, and even when this evaluation is done, it is not accompanied by targeted rehabilitation plans.
A collaboration between CIMeC (Center for Mind/Brain Sciences) of the University of Trento and the Lyon Neuroscience Research Center (France) has led to the development of a system for the three-dimensional mapping of acoustic space in people with hearing loss. The system, named SPHERE, uses the technologies of virtual reality and of recording movement in real time to guide the positioning of a loudspeaker in the three-dimensional space surrounding the person, to monitor with precision the visual information provided by an immersive virtual reality visor, to present acoustic stimuli in specific positions in the space around the head of the participant, and to measure the complexity of the motor response by simultaneously tracking the movement of the eyes, the head and the hands. The results are presented through intuitive multiplatform analysis software, which shows the distortions of the acoustic space caused by the hearing loss, concisely quantifying the difficulties of the person in perceiving the acoustic scene.
SPHERE builds 3D maps of the acoustic space using technologies that were originally developed for the entertainment industry (e.g., virtual reality for video games), and are affordable and designed to be particularly stable. Having accurate measurements, together with the monitoring of the other multisensory and motor information, allows the use of SPHERE to be extended into the area of rehabilitation. Studies are under way at the Cognition Across the Senses laboratory, based in Rovereto and Lyon, to test the potential for training the perception of acoustic space. The aim is to define the optimal strategies and parameters to implement future protocols for the rehabilitation of acoustic space perception, and to improve the ability to distinguish sounds.
