## 4pPP8. New evoked cochlear responses: Double chirp-evoked distortion products and double click-evoked otoacoustic emissions.

### Session: Thursday Afternoon, May 16

**Author: Douglas H. Keefe**

**Location: Boys Town Natl. Res. Hospital, 555 N. 30th St., Omaha, NE 68131**

**Abstract:**

A novel family of evoked OAE responses controls probe distortion using a
stimulus presentation method well-suited to research and clinical applications.
The family allows a complementary representation between DP measurements and
double click-evoked OAE measurements. Each stimulus sequence includes three,
equal-duration sub-sequences defined as follows: s[inf 1](t) is a single chirp
or click, s[inf 2](t)=(epsilon)s[inf 1](t-(tau)) is a copy of s[inf 1] with
relative amplitude (epsilon) and delay (tau) (0-5 ms), and their superposition
s[inf 12](t)=s[inf 1](t)+s[inf 2](t). The pressure response to each sub-sequence
is p[inf 1], p[inf 2], and p[inf 12], respectively. The double chirp-evoked
distortion product (2ChDP) and double click-evoked OAE (2CEOAE) are defined by
p[inf D]=p[inf 12]-p[inf 1]-p[inf 2]. This subtraction of click respones is
similar to Kemp et al. (1986) in eliminating the linear response, but differs in
that particular choices of {s[inf 1](t),(tau),(epsilon)} improve measurements of
2CEOAEs at high frequencies by eliminating time-gating, and at low frequencies
by reducing probe distortion, especially when two acoustic sources are used.
With a 16 kHz sample rate, 2ChDP and 2CEOAE responses have been obtained from
350-7900 Hz. A 2CEOAE special case is (tau)=0, resulting in a wide bandwidth,
single click-evoked OAE measurement without time-gating. Methodological
refinements in real-time artifact rejection and nonlinear coherence help reduce
noise. [Work supported by NIH Grant No. P01 DC00520.]

from ASA 131st Meeting, Indianapolis, May 1996