Investigating Compressive Nonlinearity Using Forward Masking Auditory Brainstem Response in Humans

<b>Background:</b> 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.<b>Purpose:</b> The study aimed to examine CNL using ABR parameters, such as Vth peak latency or amplitude, using probe stimuli frequencies ranging from 0.5&#8211;4 kilohertz (kHz), which employs both on- and off-frequency FM methods.<b>Research Design:</b> An experimental within-group research design was adopted for the study.<b>Study Sample:</b> The study was conducted in 31 healthy individuals aged 18&#8211;45 years (mean age of 27.88 &#177; 8.589&#8201;years).<b>Data Collection and Analysis:</b> The ABR was recorded employing a tone-on-tone FM paradigm for probe stimuli frequencies ranging from 0.5&#8211;4 kHz. The experiment was done under unmasked and forward-masked conditions (on- and off-frequency FM with varying masker intensity from 50&#8211;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 <i>t</i> test compared the slope across FM conditions.<b>Results:</b> 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&#8211;70 dB SPL in either masking condition. Additionally, the growth of masking showed a steep slope in the on-frequency FM with a smaller <i>R</i>² value.<b>Conclusions:</b> 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.