Peripheral nonlinearities (Walt Jesteadt )

Subject: Peripheral nonlinearities
From:    Walt Jesteadt  <JESTEADT(at)BOYSTOWN.ORG>
Date:    Fri, 5 Jul 1996 13:45:37 CST

I have a general question about the order of events in the peripheral auditory system and it occurred to me that it would be worthwhile to ask those of you on the auditory list. If you send responses directly to me rather than to the list as a whole, I will put together a summary and send it out. I will couch this discussion in terms of a 1995 paper in Hearing Research by Oxenham and Moore, which I think I have read and have remembered correctly. My apologies to them if I have not. They present a black box model of peripheral processing consisting of auditory filters, followed by a nonlinearity, followed by a temporal window, then a decision device. They cite other examples of similar models. Other examples exist where the filter or excitation pattern segment of peripheral models is assumed to have linear input, but later processing is not defined. There are a few others (Zwicker's specific loudness model, for example), where the filter or excitation pattern process is assumed to have nonlinear input, or to be nonlinear itself. I am curious as to what the current consensus is regarding the location of the nonlinearity and implications of that for models at the psychoacoustic level. Oxenham and Moore note two sources of assumed nonlinearity, basilar membrane mechanics and hair cell transduction. For their purposes, they lump these sources together. Only the latter source, however, clearly comes after the filter. They chose their conditions to avoid any role of the filter, so the possibility of a nonlinearity before the filter would have no impact on their particular study, but it would in many other cases. Given nonlinearity as well as frequency selectivity in the basilar membrane response, and stimuli of unequal level presented within the frequency range of a given auditory filter, should I just sum the power across frequency, as the roex program does, and assume a nonlinear transform afterwards, or should I incorporate a nonlinear transform ahead of the auditory filter, or should I do both? I would appreciate people's opinions and supporting data if such exist. If there appears to be any interest in this question, I will get a summary out to people as soon as possible. Walt Jesteadt INTERNET: jesteadt(at)BoysTown.ORG Boys Town National Research Hospital 555 North 30th Street PHONE: (402) 498-6704 Omaha, NE 68131 FAX: (402) 498-6351

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