Differences in distortion product otoacoustic emission phase recorded from human neonates using two popular probes

Abstract

DPOAE (2f(1)-f(2)) phase was measured across a 3-octave frequency range from two groups of newborns using ER10B+ and ER10C probe microphones. A marked phase shift was noted in the mid-to-high frequency range for newborn data recorded with the ER10C only. In contrast, the ER10B+ produced phase that was approximately invariant as a function of frequency for most of the range. Probe-related phase shifts can be effectively eliminated by correcting for variations in the phases of the primary tones. Results highlight the importance of detecting and correcting for system-related phase shifts so they are not misinterpreted as cochlear in origin.

Figure 1

Mean DPOAE phase (±1 SD) averaged into 1/8 octave frequency bins for two groups of newborns: 13 infants tested with the ER10C probe (squares) and a second group of 14 newborns tested with the ER10B+ probe (circles). NOTE: DPOAE phase was unwrapped starting at 500 Hz though only data points >800 Hz are displayed due to poor SNR at the lowest frequencies.

Figure 2

An example of four individual DPOAE phase vs. frequency functions from newborns tested with the ER10C probe.

Figure 3

The newborn phase data displayed in Fig. 1 are shown again in this graphic. The stippled region represents the corrected phase derived by subtracting 2ϕ₁-ϕ₂ from the estimated phase of the DPOAE, where ϕ₁, ϕ₂ are the measured phases of the two primary tones. The shaded region represents the uncorrected phase values. Because of the significant overlap, the two regions are staggered slightly for display purposes in the lower panel.

Figure 4

Mean DPOAE phase vs. frequency functions from 8 normal-hearing adults recorded with the ER10C probe (±1 SD). Data are shown corrected for variations in stimulus tone phases (stippled region) and in uncorrected form (shaded region).