Adaptive Reweighting of Auditory Localization Cues in Response to Chronic Unilateral Earplugging in Humans

Abstract

Localizing a sound source involves the detection and integration of various spatial cues present in the sound waves at each ear. Previous studies indicate that the brain circuits underlying sound localization are calibrated by experience of the cues available to each individual. Plasticity in spatial hearing is most pronounced during development but can also be demonstrated during adulthood under certain circumstances. Investigations into whether adult humans can adjust to reduced input in one ear and learn a new correspondence between interaural differences cues and directions in space have produced conflicting results. Here we show that humans of both sexes can relearn to localize broadband sounds with a flat spectrum in the horizontal plane after altering the spatial cues available by plugging one ear. In subjects who received daily training, localization accuracy progressively shifted back toward their pre-plug performance after 1 week of earplugging, whereas no improvement was seen if all trials were performed on the same day. However, localization performance did not improve on a task that used stimuli in which the source spectrum was randomized from trial to trial, indicating that monaural spectral cues are needed for plasticity. We also characterized the effects of the earplug on sensitivity to interaural time and level differences and found no clear evidence for adaptation to these cues as the free-field localization performance improved. These findings suggest that the mature auditory system can accommodate abnormal inputs and maintain a stable spatial percept by reweighting different cues according to how informative they are.

Relearning Auditory Spectral Cues for Locations Inside and Outside the Visual Field

“…While this work has also suggested that training over a period of days can accelerate accommodation to changes in auditory localization cues, this does not seem to involve a recalibration of the binaural cues (Kumpik et al 2010).…”

“…More recent work using unilateral earplugs to perturb binaural rather than monaural (spectral) cues has demonstrated the capacity for moderate levels of accommodation in mature ferrets (Kacelnik et al 2006) and humans (Kumpik et al 2010). While this work has also suggested that training over a period of days can accelerate accommodation to changes in auditory localization cues, this does not seem to involve a recalibration of the binaural cues (Kumpik et al 2010).…”

Auditory Spatial Perception: Auditory Localization

“…The available data (e.g., Kumpik et al, 2010;Nabelek et al, 1980) indicate that people can quickly re-learn natural localization cues after the cause of the altered cues has been removed, indicating that the natural neural traces in the brain are not significantly altered by learning the new cues.…”

Adaptation of Binaural Processing in the Adult Brainstem Induced by Ambient Noise

“…Behavioral studies in adult ferrets showed that unilateral earplugs produced long-term but reversible effects on binaural unmasking (Moore et al, 1999). Follow-up studies investigated the process of relearning to localize sounds after reversible occlusion of one ear, and showed that ferrets and humans improved their localization ability after a training period of only 1 week (Kacelnik et al, 2006;Kumpik et al, 2010).…”