Exploring Human Cochlear Masking and OAE Suppression at Different Cochlear Locations Using Frequency Sweeps
Creators: name: Salloom, William
name: Shera, Christopher
name: Charaziak, Karolina
Publisher: name: Zenodo
Year: 2024
Subjects: Cochlear nonlinearity
Two-tone suppression
Otoacoustic emissions
Psychoacoustics
Cochlea
Frequency sweeps

description: Background: Previous recordings of mouse basilar-membrane (BM) motion in response to exponential frequency chirps have shown that upward sweeps (i.e., from low to high frequency) are more effective suppressors of tonal probe signals than downward sweeps (high to low) (Charaziak, ARO 2022). That study found that the differential suppressive effects of sweep direction depend strongly on sweep rate, being stronger for faster sweeps. These results in mice are reminiscent of findings from human perceptual studies using so-called “Schroeder-phase complexes,” which are stimuli that contain multiple harmonic frequency components of equal amplitude but variable starting phase, summing to produce a series of periodic linear frequency sweeps. Behavioral studies find that negative Schroeder-phase maskers (e.g., upward sweeps) are more effective maskers of tonal signals than positive Schroeder-phase maskers (e.g., downward sweeps). In our recent work (Salloom et al, ARO 2023), we measured behavioral masking and OAE suppression as a function of sweep rate and direction in normal hearing humans. Consistent with the sweep direction effects in the Schroeder masking literature, the upward sweeps were more effective maskers/suppressors than downward sweeps. Unexpectedly, we found that the largest up-down differences in both behavioral masking and OAE suppression occurred at sweep rates of approximately ~50 oct/s. This rate of peak effectiveness matches otoacoustic estimates of the group velocity of the traveling wave. These results suggest that both behavioral masking and OAE suppression share common mechanisms, presumably closely related to mechanical suppression in the cochlea. 

Methods: The current study builds on our recent efforts investigating the effects of sweep rate and direction in normal hearing humans, both behaviorally and physiologically. Schroeder-phase stimuli are used in both behavioral masking and stimulus-frequency otoacoustic emissions (SFOAEs), either as maskers or suppressors, respectively. We explore the test-retest reliability of our modified SFOAE suppression paradigm to determine the consistency of our estimates of cochlear suppression. In addition, we measure the effects of sweep rate and direction at a higher signal/probe frequency (~4 kHz) to determine whether the dependence on sweep rate and direction varies with location in the cochlea. We hypothesize that the use of these stimuli will provide new opportunities to relate masking and suppression to cochlear processing. 

Results: Differences in psychoacoustic masking and OAE suppression for various sweep combinations will be explored and compared. To the extent that the two phenomena share common generation mechanisms, we expect behavioral masking and OAE suppression to depend similarly on sweep characteristics. 

Conclusions: The long-term goal of our study is to better understand dynamic aspects of nonlinear signal processing in the cochlea. Here, we expand on previous work in mice (Charaziak 2022) and humans (Salloom et al 2023) to explore the effects of frequency sweep rate and direction on signal suppression and masking in normal hearing humans.
description: If you would like to listen to our up-and-down swept stimuli configurations, please take a look at our attached QR codes!
description: This research was supported by NIH(NIDCD): T32 DC009975 (HCN), R01 DC003687 (CAS), K99/R00 DC016906 (KKC)