A method to induce swapped binaural hearing

This paper describes the application of a small hearing aid that precisely fits into a subject's ear canal (complete-in-canal, or CIC). The bandwidth of the device is about 7 kHz. The system allows for selective manipulation of the different acoustic cues used for sound localization. The potential of the system is illustrated by robustly interchanging the input of the left and right ear, and consequently changing the sign of the binaural difference cues (both interaural phase and intensity) that are used for horizontal sound localization. As a result, left-right perception is reversed, while high-frequency pinna cues are sufficiently preserved to maintain up-down localization. As the hearing condition is well-defined, the auditory system could in principle remap these cues into a new representation of sound azimuth by relating the modified cues to veridical sound locations. The hearing aids were applied in four human subjects. Swapped binaural hearing was tested in two of the subjects. Swapped localization experiments for an extended period indicated stable performance of both subjects. Interestingly, an adaptive response to the reversed interaural cues was not observed. The current system may prove useful for psychophysical studies that concern the independent processing of sound localization cues, as well as in long-term developmental and plasticity studies with animals. (C) 2002 Elsevier Science B.V. All rights reserved.