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Comparative Study
. 2011 May;129(5):3104-14.
doi: 10.1121/1.3569737.

The breaking of cochlear scaling symmetry in human newborns and adults

Carolina Abdala  1 , Sumitrajit Dhar, Srikanta Mishra
Affiliations
Comparative Study

The breaking of cochlear scaling symmetry in human newborns and adults

Carolina Abdala et al. J Acoust Soc Am. 2011 May.

Abstract

Scaling symmetry appears to be a fundamental property of the cochlea as evidenced by invariant distortion product otoacoustic emission (DPOAE) phase above ∼1-1.5 kHz when using frequency-scaled stimuli. Below this frequency demarcation, phase steepens. Cochlear scaling and its breaking have been described in the adult cochlea but have not been studied in newborns. It is not clear whether immaturities in cochlear mechanics exist at birth in the human neonate. In this study, DPOAE phase was recorded with a swept-tone protocol in three, octave-wide segments from 0.5 to 4 kHz. The lowest-frequency octave was targeted with increased signal averaging to enhance signal-to-noise ratio (SNR) and focus on the apical half of the newborn cochlea where breaks from scaling have been observed. The results show: (1) the ear canal DPOAE phase was dominated by the distortion-source component in the low frequencies; thus, the reflection component cannot explain the steeper slope of phase; (2) DPOAE phase-frequency functions from adults and infants showed an unambiguous discontinuity around 1.4 and 1 kHz when described using two- and three-segment fits, respectively, and (3) newborns had a significantly steeper slope of phase in the low-frequency portion of the function which may suggest residual immaturities in the apical half of the newborn cochlea.

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Figures

Figure 1
Figure 1
Individual DPOAE SNR in each octave segment for all adult (left column) and newborn (right column) subjects. The mean SNR for each condition is shown in red for adults and blue for newborns.
Figure 2
Figure 2
IFFT-derived DPOAE component magnitude for the distortion- and reflection-source components in three, octave-wide intervals: 0.5–1 kHz, 1–2 kHz, and 2–4 kHz. The black lines display distortion-component levels and the gray lines, reflection. Dashed lines represent ±1 SD.
Figure 3
Figure 3
DPOAE phase in octave 1 (0.5–1 kHz) and octave 2 (1–2 kHz) is shown for two newborn subjects (out of five) tested with a suppressor tone. The gray line shows phase recorded with an ipsilateral suppressor tone presented 0.1 octave below fdp. The black line shows unsuppressed DPOAE phase.
Figure 4
Figure 4
DPOAE phase versus frequency functions for 13 adult (gray) and ten newborn (black) subjects.
Figure 5
Figure 5
The DPOAE phase versus frequency functions for 13 adult subjects are shown in gray and the one-knot spline fit to model the data is superimposed as a black line.
Figure 6
Figure 6
The DPOAE phase versus frequency functions for ten newborn subjects is shown in gray and the one-knot spline fit applied to model the data is superimposed as a black line.
Figure 7
Figure 7
The upper panel shows the mean slope of phase (cyc∕kHz) modeled by the one-knot spline analysis for the low-frequency segment of the phase-frequency function, below the estimated knot frequency. Individual phase slopes for each subject are also shown (small gray x). The lower panel displays the mean knot frequency modeled by a one-knot spline analysis as well as the individual knot values (small gray circles).
See this image and copyright information in PMC

References

    1. Abdala, C. (2000). “Distortion product otoacoustic emission (2f1 − f2) amplitude growth in human adults and neonates,” J. Acoust. Soc. Am. 107, 446–456. 10.1121/1.428315 - DOI - PubMed
    1. Abdala, C., and Dhar, S. (2010a). “Distortion product otoacoustic emission (DPOAE) phase and component analysis in human newborns,” J. Acoust. Soc. Am. 127, 316–325.10.1121/1.3268611 - DOI - PMC - PubMed
    1. Abdala, C., and Dhar, S. (2010b). “DPOAE phase measured from human neonates using two popular probes,” J. Acoust. Soc. Am. 128, EL49–EL55.10.1121/1.3453415 - DOI - PMC - PubMed
    1. Abdala, C., Kalluri, R., Dhar, S., Rogers, A., and Luckovich, S. (2011). “Level dependence of DPOAE phase is attributed to component mixing,” in Poster Presented to the 34th Midwinter Meeting of the Association for Research in Otolaryngology, February 2011, #101, Baltimore, MD.
    1. Abdala, C., and Keefe, D. (2006). “Effects of middle-ear immaturity on distortion product otoacoustic emission suppression tuning in infant ears,” J. Acoust. Soc. Am. 120, 3832–3842.10.1121/1.2359237 - DOI - PubMed

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