Swept-tone stimulus-frequency otoacoustic emissions: Normative data and methodological considerations

Abstract

Stimulus-frequency otoacoustic emissions (SFOAEs) are reflection-source emissions, and are the least familiar and perhaps most underutilized otoacoustic emission. Here, normative SFOAE data are presented from a large group of 48 young adults at probe levels from 20 to 60 dB sound pressure level (SPL) across a four-octave frequency range to characterize the typical SFOAE and describe recent methodological advances that have made its measurement more efficient. In young-adult ears, SFOAE levels peaked in the low-to-mid frequencies at mean levels of ∼6-7 dB SPL while signal-to-noise ranged from 23 to 34 dB SPL and test-retest reliability was ±4 dB for 90% of the SFOAE data. On average, females had ∼2.5 dB higher SFOAE levels than males. SFOAE input/output functions showed near linear growth at low levels and a compression threshold averaging 35 dB SPL across frequency. SFOAE phase accumulated ∼32-36 cycles across four octaves on average, and showed level effects when converted to group delay: low-level probes produced longer SFOAE delays. A "break" in the normalized SFOAE delay was observed at 1.1 kHz on average, elucidating the location of the putative apical-basal transition. Technical innovations such as the concurrent sweeping of multiple frequency segments, post hoc suppressor decontamination, and a post hoc artifact-rejection technique were tested.

Swept-Tone Stimulus-Frequency Otoacoustic Emissions in Human Newborns

“…The 95% confidence intervals (dashed lines) were generated through resampling of the data. Both age groups show the strongest SFOAEs between 1 and 2 kHz, consistent with past work (Abdala, Guardia, et al., 2018; Dewey & Dhar, 2017; Ellison & Keefe, 2005). Between 3 and 5 kHz, adults show higher levels than newborns, likely due to standing-wave interference in the ear canals of these adult subjects.…”

“…SFOAEs were evoked by 40 dB SPL pure tones swept logarithmically in a downward direction at 2 oct/s from f 2 = 0.5 to 8 kHz for both newborn and adult subjects. Four-frequency segments, each roughly one-octave wide, were stacked and presented concurrently for rapid data collection (see Abdala, Guardia, et al., 2018). A suppressor tone at 55 dB SPL was simultaneously presented at a frequency ratio of 0.95 (re: probe) and a modified interleaved suppression paradigm was utilized to extract SFOAEs (Shera & Guinan, 1999).…”

“…It is likely that multiple factors contributed to these findings as will be further considered in the “Discussion” section. However, the reflection component of the DPOAE is not an ideal tool for studying human cochlear maturation: It must first be separated from the total DPOAE using one of a variety of signal processing techniques, none of which is perfect; the strength of the signal evoking the reflection part of the DPOAE cannot be well quantified (because it is the forward-going component of the distortion wave); and the reflection component of the DPOAE is typically low amplitude, making it difficult to measure and characterize well (see Abdala, Guardia, & Shera, 2018). The SFOAE provides a more direct and nonconfounded measure of intracochlear reflections.…”

“…The SFOAE provides a more direct and nonconfounded measure of intracochlear reflections. It has recently been characterized in normal-hearing young adults (Abdala, Guardia, et al., 2018; Dewey & Dhar, 2017; Mishra & Talmadge, 2018) and older adults (Abdala, Ortmann, & Shera, 2018), and the optimal testing parameters and strategies have been well defined. Characterizing the swept-tone SFOAE in newborns adds converging data to the existing literature available on functional status of the human cochlea at birth and disentangles previous methodological confounds that used less direct measures.…”

Towards a joint reflection-distortion otoacoustic emission profile: Results in normal and impaired ears

“…A novel method of sweep presentation was applied for efficiency: four sweep segments, each spanning 1.8 kHz, were presented concurrently as a stack. Recent work has shown that as long as there is at least a one-octave separation between stacked frequency segments, the impact on SFOAE amplitude and phase is negligible (Abdala et al, 2017); the advantage is that data collection time is cut to one-quarter the time required for a single sweep.…”