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.
