Investigating Compressive Nonlinearity Using Forward Masking Auditory Brainstem Response in Humans

Background: The behavioral investigation of compressive nonlinearity (CNL) can be achieved by comparing the growth of forward masking (FM) between on-frequency and off-frequency maskers. Because the off-frequency masker exhibits linear behavior at the characteristic frequency whereas the on-frequency masker functions nonlinearly, comparing the experimental outcomes using scalp-recorded auditory brainstem response (ABR) measures provides an objective estimation of auditory physiology. Purpose: The study aimed to examine CNL using ABR parameters, such as Vth peak latency or amplitude, using probe stimuli frequencies ranging from 0.5–4 kilohertz (kHz), which employs both on- and off-frequency FM methods. Research Design: An experimental within-group research design was adopted for the study. Study Sample: The study was conducted in 31 healthy individuals aged 18–45 years (mean age of 27.88 ± 8.589 years). Data Collection and Analysis: The ABR was recorded employing a tone-on-tone FM paradigm for probe stimuli frequencies ranging from 0.5–4 kHz. The experiment was done under unmasked and forward-masked conditions (on- and off-frequency FM with varying masker intensity from 50–80 decibels [dB] sound pressure level [SPL]). The data for latency and amplitude were statistically analyzed using one-way repeated measures analysis of variance (RM-ANOVA), two-way RM-ANOVA, and Bonferroni post hoc tests between and within different probe stimuli in different conditions. Further, a paired t test compared the slope across FM conditions. Results: A gradual shift in Vth peak latency and a reduction in response amplitude was observed in proportion to the increase in masker intensity for both masking conditions across all probe stimuli, with a more pronounced shift in on-frequency FM. However, no significant difference in latency was found between the masker intensities of 60–70 dB SPL in either masking condition. Additionally, the growth of masking showed a steep slope in the on-frequency FM with a smaller R 2 value. Conclusions: Objective electrophysiologic measures are instrumental in accurately estimating CNL because these measures provide robust, efficient, and reliable insights into the intricate functioning of the auditory system without reliance on a subjective behavioral response.