Does masking alter the mismatch negativity response to gaps?

Abstract

Objective

Difficulties perceiving speech in noise can be studied using temporal resolution measures. This study investigates the processing of silent gaps in the central auditory system in various noise conditions.

Methods

Event-related potentials and psychoacoustic thresholds were measured in 14 normal hearing adult subjects. A multi-deviant paradigm was used to present an 80  dB SPL standard stimulus and a series of gapped deviants with gap durations ranging from 2 to 40  ms. The stimuli were presented in three noise conditions in which the noise (i.e. the masker) was either absent, presented at a low intensity (60  dB SPL) or high intensity (80  dB SPL). A composite N1 + mismatch negativity called a deviant-related negativity (DRN) and the following positive component (P2) measured peak-to-peak were compared to behavioral accuracy rates.

Results

The amplitude of the DRN-P2 increased as gap duration increased in the no and low masking conditions. However, this was not the case in the high masking condition. Behavioral gap detection correlated with all masking conditions. However, with high intensity masking, the gap detection accuracy was reduced, and the peak-to-peak measurement was no longer able to reliably code the temporal aspects of the signal.

Conclusions

This study demonstrates that high masking noise make the detection of gaps very difficult as demonstrated by using electrophysiology and behavioural measures. However, low levels of masking have little effect on the presence of the gap and the auditory system appears to withstand some level of noise with results similar to no masking at all.