ESTIMATING COCHLEAR FILTER RESPONSE PROPERTIES FROM DISTORTION-PRODUCT OTOACOUSTIC EMISSION (DPOAE) PHASE DELAY MEASUREMENTS IN NORMAL-HEARING HUMAN ADULTS

This study examined cochlear filter response properties derived from f (1)- and f(2)-sweep phase delay difference measures in 60 normal heari ng human adults. Seven different f(2) frequencies ranging from 1.1 to 9.2 kHz were presented (f(2)/f(1) ratios of 1.1-1.3). F-2 intensity le vel was varied in 5 dB steps from 30 to 50 dB SPL (the level of f(1) w as 15 dB above the level of f(2)). DPOAE delay estimates in a f(2)-swe ep paradigm are longer than in a f(1)-sweep paradigm at the same frequ ency and intensity. This indicates that the f(2)-sweep DPOAE phase del ay is composed of a greater proportion of the filter response time at the site of DPOAE generation than the f(1)-sweep delay. This proportio n was isolated by subtracting f(1)-sweep DPOAE delays from f(2)-sweep delays at similar f(2) frequencies and intensities. Under the assumpti on of linearity and minimum phase the impulse response of the filter a t each f(2) stimulus level was calculated from the mean phase delay di fference. Frequency response properties were calculated by Fourier tra nsformation of the impulse response at each f(2) frequency and intensi ty. High frequency low intensity impulse responses had longer response times and narrower frequency bandwidths than low frequency high inten sity responses. The Q(10dB) values of DPOAE derived tuning curves rang ed from 2.4 (1.5 kHz) to 7.3 (8.5 kHz). (C) 1998 Elsevier Science B.V.