Hyojin Kim1, Viktorija Ratkute1, Bastian Epp1
1Hearing Systems section, Department of Health Technology, Technical University of Denmark, Lyngby, Denmark
Comodulated masking noise and interaural phase disparity (IPD) can enhance detection of masked signals. Such enhancement in detection performance, or masking release, can be quantified as decreased detection thresholds: comodulation masking release (CMR) and binaural masking level difference (BMLD). While many studies investigated CMR and BMLD, the relevance of masking release at supra-threshold levels is still unclear. Here, we used both psychoacoustic and electro-physiological measures to investigate how CMR and BMLD affect intensity discrimination at supra-threshold levels.
We designed eight masking release conditions where each condition induces different amount of CMR and BMLD. In the psychoacoustic experiment, we investigated whether the difference in the amount of masking release will affect listening at supra-threshold levels. We used intensity just-noticeable difference (JND) to quantify an increase in salience of the tone. For instance, the salience of the tone would increase when the level of the tone is increased by JND. That is, the condition with lower JND would be more salient than the one with higher JND at the same supra-threshold level. As a physiological correlate of JND, we investigated late auditory evoked potentials (LAEPs) with electroencephalography (EEG). We measured P2 at supra-threshold levels from +15 dB to + 25 dB. Our hypothesis was that the increment in P2 with increasing tone level would be inversely proportional to JND.
From the psychoacoustic experiment, we found that JNDs highly depend on the level of the tone. The JNDs were equal at the same intensity of the tone rather than at the same supra-threshold levels. The results from the EEG experiment showed an inverse correlation between the intensity JND and the amplitude of P2. In conclusion, the amplitude of P2 can reflect the salience of masked tone at supra-threshold levels.