Subject: Re: sounds too loud From: Martin Braun <nombraun(at)POST.NETLINK.SE> Date: Sun, 21 Jan 2001 14:10:51 +0100Jont Allen wrote: > Does anybody know of a condition where a person complains that sounds a= re too loud. > Does this condition have a name? > Is it a physiological condition, with a known cause? There is a large clinical survey on this issue: Hallpike and Hood (1959) measured recruitment and over-recruitment in 200 patients with unilateral Meni=E8re's disease. The applied audiological technique was the "alternate binaural loudness balance" (Fouler test). Al= l 200 patients showed recruitment in the affected ear, no matter if this ea= r had any significant hearing loss or not. Most importantly, two-thirds of these ears also showed over-recruitment. Over-recruitment means (as correctly reported to this list on Jan 19 by Brent Edwards) that above a certain sound level, say 80 dB, the affected ear hears louder than the healthy ear. Hallpike, C.S. and Hood, J.D. (1959) Observations upon the neurological mechanism of the loudness recruitment phenomenon. Acta Otolaryngol. (Stockh.) 50, 472-486. [The discussion of possible causes is no longer useful today, but the empirical data are classical.] Because Meni=E8re's disease is a cochlear-vestibular disease, hyperacusis= in these patients is assumed to have cochlear origins. Hair cell damages can not be a necessary element, because even affected ears without hearing lo= ss often have hyperacusis. The only plausible hypothesis is a mechanical one. Expansion of the inner ear endolymph (called "endolymphatic hydrops"), wh= ich is present in all cases of Meni=E8re's disease, displaces various cochlea= r components and reduces the normal cochlea's capacity of absorbing high-le= vel acoustic energy. The loss of inner-ear dampening leads to an increased ha= ir cell excitation, and thus increased loudness sensation, at medium and hi= gh sound levels. A large amount a experimental and clinical evidence on the relation of hyperacusis and inner ear mechanics was reviewed by Braun (1996). Braun, M. (1996) Impediment of basilar membrane motion reduces overload protection but not threshold sensitivity: evidence from clinical and experimental hydrops. Hear Res 97, 1-10. Martin Martin Braun Neuroscience of Music Gansbyn 14 S-671 95 Kl=E4ssbol Sweden nombraun(at)post.netlink.se