This study examines auditory brainstem responses (ABR) elicited by rising frequency chirps. The time course of frequency change for the chirp theoretically produces simultaneous displacement maxima by compensating for travel-time differences along the cochlear partition. This broadband chirp was derived on the basis of a linear cochlea model [de Boer, "Auditory physics. Physical principles in hearing theory I," Phys. Rep. 62, 87-174 (1980)]. Responses elicited by the broadband chirp show a larger wave-V amplitude than do click-evoked responses for most stimulation levels tested. This result is in contrast to the general hypothesis that the ABR is an electrophysiological event most effectively evoked by the onset or offset of an acoustic stimulus, and unaffected by further stimulation. The use of this rising frequency chirp enables the inclusion of activity from lower frequency regions, whereas with a click, synchrony is decreased in accordance with decreasing traveling velocity in the apical region. The use of a temporally reversed (falling) chirp leads to a further decrease in synchrony as reflected in ABR responses that are smaller than those from a click. These results are compatible with earlier experimental results from recordings of compound action potentials (CAP) [Shore and Nuttall, "High synchrony compound action potentials evoked by rising frequency-swept tonebursts," J. Acoust. Soc. Am. 78, 1286-1295 (1985)] reflecting activity at the level of the auditory nerve. Since the ABR components considered here presumably reflect neural response from the brainstem, the effect of an optimized synchronization at the peripheral level can also be observed at the brainstem level. The rising chirp may therefore be of clinical use in assessing the integrity of the entire peripheral organ and not just its basal end.
This study examines the usefulness of the upward chirp stimulus developed by Dau et al. [J. Acoust. Soc. Am. 107, 1530-1540 (2000)] for retrieving frequency-specific information. The chirp was designed to produce simultaneous displacement maxima along the cochlear partition by compensating for frequency-dependent traveling-time differences. In the first experiment, auditory brainstem responses (ABR) elicited by the click and the broadband chirp were obtained in the presence of high-pass masking noise, with cutoff frequencies of 0.5, 1, 2, 4, and 8 kHz. Results revealed a larger wave-V amplitude for chirp than for click stimulation in all masking conditions. Wave-V amplitude for the chirp increased continuously with increasing high-pass cutoff frequency while it remains nearly constant for the click for cutoff frequencies greater than 1 kHz. The same two stimuli were tested in the presence of a notched-noise masker with one-octave wide spectral notches corresponding to the cutoff frequencies used in the first experiment. The recordings were compared with derived responses, calculated offline, from the high-pass masking conditions. No significant difference in response amplitude between click and chirp stimulation was found for the notched-noise responses as well as for the derived responses. In the second experiment, responses were obtained using narrow-band stimuli. A low-frequency chirp and a 250-Hz tone pulse with comparable duration and magnitude spectrum were used as stimuli. The narrow-band chirp elicited a larger response amplitude than the tone pulse at low and medium stimulation levels. Overall, the results of the present study further demonstrate the importance of considering peripheral processing for the formation of ABR. The chirp might be of particular interest for assessing low-frequency information.
This study examines the question of whether the neurophysiological events reflected by the auditory evoked potentials are similar to the events underlying loudness perception. Recent studies showed that, at brainstem level, loudness does not seem to be directly related to the potential amplitude (wave V). This is the case for the loudness growth function for tone pulses [J. K. Nousak and D. R. Stapells, ‘‘Loudness and the ABR/MBR in noise-masked normal-hearing subjects,’’ ARO meeting, p. 39 (1998)] as well as for loudness summation obtained with optimized chirp stimuli [Wegner et al., ‘‘Untersuchungen zu Lautheitskorrelaten in akustisch evozierten Potentialen,’’ DAGA 98, Zürich (in press)]. In both conditions, the results obtained with early evoked potentials suggest a higher compression as that normally derived from psychophysical data and as reflected in common loudness models. This study presents brainstem and cortical potentials evoked by bandlimited stimuli of equal loudness. The role of the synchronization, stimulation rate, and temporal integration at both processing levels is discussed.
Previous work on loudness perception was primarily focused on stationary stimuli. However, knowledge about the processing and perception of temporally varying sounds is of special interest for various applications, such as, e.g., speech perception and hearing aids. We therefore studied the loudness of brief sounds both with psychophysical and electrophysiological methods (i.e., auditory evoked potentials) as a function of the stimulus bandwidth. The loudness summation effect appeared to be larger for brief stimuli than for long stimuli. Also, the magnitude of wave V in ABR recordings for brief stimuli with equal subjective loudness was found to depend on the stimulus bandwidth. Both results indicate that the effective compression for short signals is larger than for long signals. This finding is in conflict with predictions derived with current loudness models or with a model of the effective processing in the auditory system. The consequences of these findings for the nonlinear compression stage in auditory models will be discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.