ON THE ROLE OF THE OLIVOCOCHLEAR BUNDLE IN HEARING - 16 CASE-STUDIES

Earlier we presented data (Scharf et al. (1994) Hear. Res. 75, 11-26) from a young patient (S.B.) who had undergone a vestibular neurotomy, during which the olivocochlear bundle (OCB) was severed. Those data ar e complemented by measurements on 15 other patients - some like S.B. w ith normal audiometric thresholds, none with a loss greater than 35 dB at experimental frequencies. Comparisons of performance for the same ear before and after surgery or between the operated and healthy ears do not provide evidence that the lack of OCB input impairs the followi ng psychoacoustical functions: (I) detection of tonal signals, (2) int ensity discrimination, (3) frequency selectivity, (4) loudness adaptat ion, (5) frequency discrimination within a tonal series, (6) in-head l ateralization. Data on single-tone frequency discrimination are equivo cal. These mostly negative results apply to listening both in the quie t and, where relevant, in noise. The only clear change in hearing afte r a vestibular neurotomy is that most patients detect signals at unexp ected frequencies better than before. This change suggests an impaired ability to focus attention in the frequency domain. Although limited in scope, our finding that human hearing without OCB input is essentia lly normal agrees with much of the relevant literature on animal behav ior and with the patients' self-reports.