Informational and Energetic Masking Effects on Speech-Evoked Cortical Auditory Potentials

Three experiments were undertaken to evaluate the effect of informational and energetic masking on obligatory and cognitive auditory evoked potentials, as well as perceptual responses, to speech and non-speech tokens. Perception of speech in noise is one of the more challenging tasks in which listeners engage. Understanding how the brain processes speech in noise helps clinicians develop therapies and outcome measures to assist individuals who struggle understanding speech in noise. The experiments were carried out in 15 young adult listeners with normal hearing. In Experiment I, the CAEP onset and acoustic change complex responses were obtained in response to vowel-consonant-vowel and tone-change tokens in quiet, and in three masker conditions, speech-shaped noise, 8-talker babble and 2-talker babble. In Experiment II, the same participants completed a VCV identification task in quiet, and with the three maskers used in Experiment I. In Experiment III the P300 was obtained while listeners were asked to identify tokens when presented in quiet and in the three masking conditions used previously. Experiment I results demonstrated that the introduction of maskers reduced the amplitude of the CAEP onset and ACC responses, for both VCV and tone-change tokens, and that the 2-talker babble masker had a greater effect on the responses to VCV tokens than to tone-change (non-speech) tokens. These effects were specific to the P2 component of the cortical onset response. The results of Experiment II revealed that the identification of only certain VCV-tokens were affected by the introduction of masking, and there was no differential effect of energetic vs. informational masking. In Experiment III, only the 2-talker babble reduced the P300 response amplitudes, indicating an effect of informational masking on the electrophysiologic response that was not seen in behavioral task of Experiment II. The differential effects of informational masking on auditory evoked potentials may be related to its acoustic parameters. The informational masker used in this study (2-talker babble) had a 5 Hz amplitude modulation that may evoke a phase-locked response, diminishing the neural complement that would otherwise respond to the stimulus. Differences in calibration of modulated vs. unmodulated maskers may also contribute to the effects seen. In addition, the spectral-temporal characteristics of the masker relative to the stimulus (speech or non-speech) can play a role. This study provides new knowledge about how the brain responds in a challenging listening situation when there is informational masking. The findings can contribute to developing clinical methods for diagnosis and/or prognosis of speech-in-noise problems that often drives people to seek hearing health care.