Inter-modality influence on the brainstem using an arithmetic exercise.

This study investigates the inter-modality influence on the brainstem using a mental task (arithmetic exercise). Frequency Following Responses were recorded in quiet and noise, across four stimuli conditions (No Task, Easy, Medium, and Difficult). For the No Task, subjects were instructed to direct their attention to the presented speech vowel while no mental task was performed. For the Easy, Medium, and Difficult conditions, subjects were instructed to direct their attention to the mental task while ignoring simultaneously presented speech vowel /a/. Results from this study suggest that top-down influences such as selective attention and working memory have no significant effects at the level of the brainstem in both listening backgrounds (quiet and noise).

Effects of Early- and Late-Arriving Room Reflections on the Speech-Evoked Auditory Brainstem Response.

BACKGROUND: Room reverberation alters the acoustical properties of the speech signals reaching our ears, affecting speech understanding. Therefore, it is important to understand the consequences of reverberation on auditory processing. In perceptual studies, the direct sound and early reflections of reverberated speech have been found to constitute useful energy, whereas the late reflections constitute detrimental energy. PURPOSE: This study investigated how various components (direct sound versus early reflections versus late reflections) of the reverberated speech are encoded in the auditory system using the speech-evoked auditory brainstem response (ABR). RESEARCH DESIGN: Speech-evoked ABRs were recorded using reverberant stimuli created as a result of the convolution between an ongoing synthetic vowel /a/ and each of the following room impulse response (RIR) components: direct sound, early reflections, late reflections, and full reverberation. Four stimuli were produced: direct component, early component, late component, and full component. STUDY SAMPLE: Twelve participants with normal hearing participated in this study. DATA COLLECTION AND ANALYSIS: Waves V and A amplitudes and latencies as well as envelope-following response (EFR) and fine structure frequency-following response (FFR) amplitudes of the speech-evoked ABR were evaluated separately with one-way repeated measures analysis of variances to determine the effect of stimulus. Post hoc comparisons using Tukey's honestly significant difference test were performed to assess significant differences between pairs of stimulus conditions. RESULTS: For waves V and A amplitudes, a significant difference or trend toward significance was found between direct and late components, between direct and full components, and between early and late components. For waves V and A latencies, significant differences were found between direct and late components, between direct and full components, between early and late components, and between early and full components. For the EFR and FFR amplitudes, a significant difference or trend toward significance was found between direct and late components, and between early and late components. Moreover, eight, three, and one participant reported the early, full, and late stimuli, respectively, to be the most perceptually similar to the direct stimulus. CONCLUSIONS: The stimuli that are acoustically most similar (direct and early) result in electrophysiological responses that are not significantly different, whereas the stimuli that are acoustically most different (direct and late, early and late) result in responses that are significantly different across all response measures. These findings provide insights toward the understanding of the effects of the different components of the RIRs on auditory processing of speech.

Speech-evoked auditory brainstem responses in children with hearing loss.

OBJECTIVE: The main objective of the present study was to investigate subcortical auditory processing in children with sensorineural hearing loss. METHODS: Auditory Brainstem Responses (ABRs) were recorded using click and speech/da/stimuli. Twenty-five children, aged 6-14 years old, participated in the study: 13 with normal hearing acuity and 12 with sensorineural hearing loss. RESULTS: No significant differences were observed for the click-evoked ABRs between normal hearing and hearing-impaired groups. For the speech-evoked ABRs, no significant differences were found for the latencies of the following responses between the two groups: onset (V and A), transition (C), one of the steady-state wave (F), and offset (O). However, the latency of the steady-state waves (D and E) was significantly longer for the hearing-impaired compared to the normal hearing group. Furthermore, the amplitude of the offset wave O and of the envelope frequency response (EFR) of the speech-evoked ABRs was significantly larger for the hearing-impaired compared to the normal hearing group. CONCLUSIONS: Results obtained from the speech-evoked ABRs suggest that children with a mild to moderately-severe sensorineural hearing loss have a specific pattern of subcortical auditory processing. Our results show differences for the speech-evoked ABRs in normal hearing children compared to hearing-impaired children. These results add to the body of the literature on how children with hearing loss process speech at the brainstem level.

Self-masking and overlap-masking from reverberation using the speech-evoked auditory brainstem response.

This study introduces an improved method to investigate the effects of reverberation using the speech-evoked auditory brainstem response (ABR) that more realistically captures the influence of self- and overlap-masking induced by room reverberation. Speech-evoked ABR was measured under three acoustic scenarios: anechoic, mild reverberation with dominance of early reflections, and severe reverberation with dominance of late reverberation. Responses were significantly weaker and had longer latencies with severe reverberation relative to anechoic and mild reverberation. Although larger responses and shorter latencies were observed with mild reverberation than anechoic, possibly due to early reflections, these reached significance in only one of six ABR response measures.