Enhanced mismatch negativity in harmonic compared with inharmonic sounds.

Many natural sounds have frequency spectra composed of integer multiples of a fundamental frequency. This property, known as harmonicity, plays an important role in auditory information processing. However, the extent to which harmonicity influences the processing of sound features beyond pitch is still unclear. This is interesting because harmonic sounds have lower information entropy than inharmonic sounds. According to predictive processing accounts of perception, this property could produce more salient neural responses due to the brain's weighting of sensory signals according to their uncertainty. In the present study, we used electroencephalography to investigate brain responses to harmonic and inharmonic sounds commonly occurring in music: Piano tones and hi-hat cymbal sounds. In a multifeature oddball paradigm, we measured mismatch negativity (MMN) and P3a responses to timbre, intensity, and location deviants in listeners with and without congenital amusia-an impairment of pitch processing. As hypothesized, we observed larger amplitudes and earlier latencies (for both MMN and P3a) in harmonic compared with inharmonic sounds. These harmonicity effects were modulated by sound feature. Moreover, the difference in P3a latency between harmonic and inharmonic sounds was larger for controls than amusics. We propose an explanation of these results based on predictive coding and discuss the relationship between harmonicity, information entropy, and precision weighting of prediction errors.

Comparing methods of analysis in pupillometry: application to the assessment of listening effort in hearing-impaired patients.

Numerous studies showed that task-evoked pupil dilation is an objective marker of cognitive activity and listening effort. However, these studies differ in their experimental and analysis methods. Whereas most studies focus on a single method, the present study sought to compare different pupil-dilation data analysis methods, including different normalization techniques, baseline periods, and baseline durations, in order to assess their influence on the outcomes of pupillometry results obtained in an auditory task. To that purpose, we used pupillometry data recorded in response to words in noise in hearing-impaired individuals. The start-time of the baseline relative to stimulus timing turned out to have a significant influence on conclusions. In particular, a significant interaction in the effects of signal-to-noise ratio and hearing-aid use on pupil dilation was observed when the baseline period used started early relative to the word-an effect likely related to anticipatory, pre-stimulus cognitive processes, such as attention mobilization. This was the case even with only correct-response trials included in analyses, so that any confounding effect of performance in the word-repetition task was eliminated. Different normalization methods and baseline durations showed similar results, however the use of z-score transformation homogenized variability across conditions without affecting the qualitative aspect of the results. The consistency of results regardless of normalization methods, and the fact that differences in pupil dilation and subjective measures of listening effort could be observed despite perfect performance in the task, underlines the relevance of pupillometry as an objective measure of listening effort.

Rapid Assessment of Non-Verbal Auditory Perception in Normal-Hearing Participants and Cochlear Implant Users.

In the case of hearing loss, cochlear implants (CI) allow for the restoration of hearing. Despite the advantages of CIs for speech perception, CI users still complain about their poor perception of their auditory environment. Aiming to assess non-verbal auditory perception in CI users, we developed five listening tests. These tests measure pitch change detection, pitch direction identification, pitch short-term memory, auditory stream segregation, and emotional prosody recognition, along with perceived intensity ratings. In order to test the potential benefit of visual cues for pitch processing, the three pitch tests included half of the trials with visual indications to perform the task. We tested 10 normal-hearing (NH) participants with material being presented as original and vocoded sounds, and 10 post-lingually deaf CI users. With the vocoded sounds, the NH participants had reduced scores for the detection of small pitch differences, and reduced emotion recognition and streaming abilities compared to the original sounds. Similarly, the CI users had deficits for small differences in the pitch change detection task and emotion recognition, as well as a decreased streaming capacity. Overall, this assessment allows for the rapid detection of specific patterns of non-verbal auditory perception deficits. The current findings also open new perspectives about how to enhance pitch perception capacities using visual cues.