Amplitude of distortion product otoacoustic emissions in the guinea pig in f1- and f2-sweep paradigms

Abstract

The amplitude versus frequency relations of distortion product otoacoustic emissions (DPOAEs) were studied in the guinea pig, using both the f 1- and the f 2-sweep paradigms to vary the primary frequency separation. The amplitude of the DPOAEs 2 f 1− f 2, 3 f 1−2 f 2, 4 f 1−3 f 2, and 2 f 2− f 1, plotted as a function of DP frequency, exhibited a bandpass structure. The separation of the primaries for which the DPOAE level is maximum is referred to as the optimum ratio f 2/ f 1. For the lower sideband DPOAEs ( f dp< f 1, f 2), the optimum ratio varies non-monotonically with the primary frequency region. At an f 2 around 4.4 kHz, the optimum ratio for 2 f 1− f 2 reaches a maximum of about 1.46 while elsewhere it is in the more commonly found 1.2–1.3 range. The width of the amplitude profiles was studied by determining their Q 10 dB. The f 2-sweep yielded significantly larger Q 10 dB than f 1-sweep, for the lower sideband DPOAEs. The amplitude versus frequency functions of the lower sideband DPOAEs approximately line up. Upon closer inspection, however, with f 1-sweep the 2 f 1− f 2 DPOAE has its maximum at a slightly smaller DP frequency than the higher order DPOAEs. With f 2-sweep, on the contrary, the 2 f 1− f 2 tends to peak at a higher DP frequency than the other lower sideband distortion products. When the amplitude is considered as a function of the ratio between f dp and f 2, the difference between f 1- and f 2-sweep with respect to the width and the alignment of the amplitude functions disappears. The amplitude profiles of the lower sideband DPOAEs are a function of the DPOAE frequency f dp relative to f 2.