Neural correlates of masked and unmasked tones: psychoacoustics and late auditory evoked potentials (LAEPs)

Hearing thresholds are commonly used to quantify a listeners ability to detect sound. In the presence of masking sounds, hearing thresholds can vary depending on the signal properties of the target and the masker, commonly referred to as auditory cues. Target detection can be facilitated with comodulated masking noise and interaural phase disparity (IPD). This can be quantified with a decrease in detection thresholds or masking release: comodulation masking release (CMR, for comodulation) and binaural masking level difference (BMLD, for IPD). As these measures only reflect the low limit of levels for target detection, the relevance of masking release at supra-threshold levels is still unclear. Here, we used psychoacoustic and electrophysiological measures to investigate the effect of masking release for a masked tone at supra-threshold levels. Behaviorally, we investigated how the amount of masking release affects the salience at supra-threshold levels. We used intensity just-noticeable difference (JND) to quantify level-dependent changes in the salience of the tonal signal. As a physiological correlate, we investigated late auditory evoked potentials (LAEPs) with electroencephalography (EEG). The results showed that the intensity JNDs were equal at the same physical target tone level, regardless of the presence or absence of masking release. Estimated salience was correlated with the amount of masking release. However, salience measures across conditions converged with the target tone level above 70 dB SPL. For the LAEPs, the P2 amplitudes were more closely linked to behavioral measures than the N1 amplitudes. Both behavioral and electrophysiological measures suggest that the salience of a masked tone at supra-threshold levels is correlated with the amount of masking release.