THE PLASTIC EAR: COPING WITH A LIFETIME OF CHANGE

The shape of the pinna results in spectral cues to sound location. Over a life time the pinna shape changes. Previous work has demonstrated that, over several weeks, subjects can learn new spectral cues for locations in the audio-visual (AV) region of space. In this study we examined the extent and time course of relearning for spatial locations inside and outside the AV region. Silicon moulds were worn in the pinnae of 8 subjects for up to 62 days and auditory localization performance was measured for 76 locations surrounding the listener. There was a significant increase in the cone-of-confusion errors and decreased elevation accuracy when the moulds were first inserted consistent with the disruption of spectral cues. Performance improved significantly for all subjects over accommodation periods of 30 to 62 days but remained significantly above control. During the accommodation, localisation performance did not show a linear improvements but was characterised by cyclic changes with a period of many days. Performance error at the end of accommodation period can be attributed in part to reduced spectral information in the “new” spectral cues and/or to re-learning beyond 5 weeks.