Biology subjects

Mehta, A. H.

Publications and source records attributed to Mehta, A. H..

3 recordsLinked to original sources

bioRxiv2026

Impacts of heminode disruption on auditory processing of noisy sound stimuli

Hidden hearing loss (HHL) is an auditory neuropathy characterized by altered auditory nerve responses despite normal hearing thresholds. Recent experimental and computational studies suggest that permanent disruptions to heminode positions in spiral ganglion neuron (SGN) fibers can contribute to these deficits. However, the interaction between heminode disruption and noisy backgrounds ubiquitous in daily listening remains unexplored. This study investigates how background noise affects auditory processing with these peripheral disorders and how deficits propagate to downstream sound localization circuits in the superior olivary complex. We developed computational models of SGN fibers with mild and severe degrees of heminode disruption, subjected to sinusoidal tone stimuli in the presence of background noise with varying spectral characteristics. We analyzed the phase-locking of SGN fiber responses to the stimulus tone and modeled the subsequent effects on interaural time difference (ITD) sensitivity in the medial superior olive (MSO) using a binaural localization network. We found that near-tone-frequency noise disrupted SGN phase locking through cycle-to-cycle variability in spike phases, with effects consistent across tone frequencies. Mild heminode disruption produced frequency-dependent degradation in SGN phase locking, with effects observed only at higher frequencies tested (600-1000 Hz), without reducing overall firing rates. Critically, the effects of noise and heminode disruption were additive, with combined exposure leading to reduced ITD sensitivity and large temporal fluctuations in MSO responses. Severe heminode disruption, which additionally reduced firing rates at the SGN fibers and subsequent stages, produced profound localization deficits across all frequencies tested. Thus, our model results suggest that noisy environments exacerbate auditory deficits from peripheral disorders implicated in HHL and could potentially impair speech intelligibility through degradation in localization ability. This model may be useful for understanding the downstream impacts of SGN neuropathies.

neuroscience↗

bioRxiv2025

Dissociating the neural codes for multiple pitch perception in humans

Pitch is crucial for speech and music perception, yet its neural code remains contested. The classic rate-place theory suggests that pitch is computed from spatial patterns of average neural firing rates along the cochlear tonotopic axis. These cues are thought to be robust for isolated harmonic complex tones (HCTs) but degraded for spectrally dense mixtures of simultaneous HCTs (e.g., musical chords) due to auditory filtering. In many cases, pitch perception remains feasible for HCT mixtures, but it is unclear whether listeners utilize residual rate-place cues or alternative neural codes. To adjudicate between these possibilities, we generated rate-place metamers (META), which are synthetic stimuli with simulated auditory-nerve average-rate responses that are nearly identical to those of original pitch-evoking stimuli (ORIG). Using these stimuli, listeners completed four psychophysical experiments that spanned a wide range of acoustic and cognitive complexity, from single-HCT pitch discrimination to harmonic-expectation judgments. Combining the behavioral data with predictive models of listener performance, we found that listener performance on single pitch discrimination tasks could be adequately explained by a rate-place model, with or without simultaneous pitch maskers (Experiments 1 and 2). More complex tasks involving attention to all pitches in a three-pitch mixture (Experiments 3 and 4) showed a pattern of results more difficult to account for with a rate-place model, perhaps suggesting a role for integration of temporal cues. Significance StatementEveryday listening typically involves parsing or integrating several simultaneous pitches, for example, while listening to music or conversations in noisy environments, rather than hearing a single, isolated pitch. Despite their ubiquity, the neural mechanisms for encoding multiple pitches are not well understood, which partly explains the limitations of modern assistive listening devices in noisy settings. To address this, we developed model-based synthetic stimuli to measure how distinct pitch cues contribute to pitch perception. This approach advances our understanding of the neural basis of music perception, with a goal of informing the design of more effective hearing prostheses.

neuroscience↗

bioRxiv2018

Neural correlates of auditory enhancement in humans

The perception of sensory events can be suppressed or enhanced by the surrounding spatial and temporal context in ways that help in detecting novel objects and establishing perceptual constancy. In the auditory system, the phenomenon known as auditory enhancement reflects a general principle of contrast enhancement, where a target sound embedded within a background sound becomes perceptually more salient if the background is presented first by itself. This effect is highly robust, producing an effective enhancement of the target of between 5 and 25 dB (more than two orders of magnitude in intensity), depending on the task. Despite their ubiquity in vision, neural correlates of auditory contrast enhancement have yet to be identified in humans. Here we used the auditory steady-state response to probe the neural response to a target sound under conditions of enhancement. The probe was simultaneously modulated in amplitude with two modulation frequencies, to distinguish cortical from subcortical contributions to this phenomenon. We found robust auditory cortical, but not subcortical, enhancement that correlates with behavior and is consistent with an early theoretical model that postulates neural adaptation of inhibition. Our findings provide empirical support for a previously unverified theory of auditory enhancement and point to new approaches for improving sensory prostheses for hearing loss, such as hearing aids and cochlear implants. Significance StatementA target sound embedded within a background sound becomes perceptually more salient if the background is presented first by itself. This phenomenon, where the target "pops out", is known as auditory enhancement. It reflects a general principle of contrast enhancement, and helps in the detection of new acoustic events in the environment and in establishing the perceptual constancy of speech and other biologically relevant sounds under varying acoustic conditions. We use EEG in humans to reveal a cortical correlate of this perceptual phenomenon that provides empirical support for a longstanding but previously unverified theoretical account.

neuroscience↗