Effects of hearing loss and age on the binaural processing of temporal envelope and temporal fine structure information

Within the cochlea, broadband sounds like speech and music are filtered into a series of narrowband signals, each with a relatively slowly varying envelope (ENV) imposed on a rapidly oscillating carrier (the temporal fine structure, TFS). Information about ENV is conveyed by the timing and short-term rate of action potentials in the auditory nerve while information about TFS is conveyed by synchronization of action potentials to a specific phase of the waveform in the cochlea (phase locking). This paper describes the effects of age and hearing loss on the binaural processing of ENV and TFS information, i.e. on the processing of differences in ENV and TFS at the two ears. The binaural processing of TFS information is adversely affected by both hearing loss and increasing age. The binaural processing of ENV information deteriorates somewhat with increasing age but is only slightly affected by hearing loss. The reduced TFS processing abilities found for older/hearing-impaired subjects may partially account for the difficulties that such subjects experience in complex listening situations when the target speech and interfering sounds come from different directions in space.

Reduced object related negativity response indicates impaired auditory scene analysis in adults with autistic spectrum disorder

Auditory Scene Analysis provides a useful framework for understanding atypical auditory perception in autism. Specifically, a failure to segregate the incoming acoustic energy into distinct auditory objects might explain the aversive reaction autistic individuals have to certain auditory stimuli or environments. Previous research with non-autistic participants has demonstrated the presence of an Object Related Negativity (ORN) in the auditory event related potential that indexes pre-attentive processes associated with auditory scene analysis. Also evident is a later P400 component that is attention dependent and thought to be related to decision-making about auditory objects. We sought to determine whether there are differences between individuals with and without autism in the levels of processing indexed by these components. Electroencephalography (EEG) was used to measure brain responses from a group of 16 autistic adults, and 16 age- and verbal-IQ-matched typically-developing adults. Auditory responses were elicited using lateralized dichotic pitch stimuli in which inter-aural timing differences create the illusory perception of a pitch that is spatially separated from a carrier noise stimulus. As in previous studies, control participants produced an ORN in response to the pitch stimuli. However, this component was significantly reduced in the participants with autism. In contrast, processing differences were not observed between the groups at the attention-dependent level (P400). These findings suggest that autistic individuals have difficulty segregating auditory stimuli into distinct auditory objects, and that this difficulty arises at an early pre-attentive level of processing.

A framework for testing and comparing binaural models

Auditory research has a rich history of combining experimental evidence with computational simulations of auditory processing in order to deepen our theoretical understanding of how sound is processed in the ears and in the brain. Despite significant progress in the amount of detail and breadth covered by auditory models, for many components of the auditory pathway there are still different model approaches that are often not equivalent but rather in conflict with each other. Similarly, some experimental studies yield conflicting results which has led to controversies. This can be best resolved by a systematic comparison of multiple experimental data sets and model approaches. Binaural processing is a prominent example of how the development of quantitative theories can advance our understanding of the phenomena, but there remain several unresolved questions for which competing model approaches exist. This article discusses a number of current unresolved or disputed issues in binaural modelling, as well as some of the significant challenges in comparing binaural models with each other and with the experimental data. We introduce an auditory model framework, which we believe can become a useful infrastructure for resolving some of the current controversies. It operates models over the same paradigms that are used experimentally. The core of the proposed framework is an interface that connects three components irrespective of their underlying programming language: The experiment software, an auditory pathway model, and task-dependent decision stages called artificial observers that provide the same output format as the test subject.

The Binaural Interaction Component in Barn Owl (Tyto alba) Presents few Differences to Mammalian Data

The auditory brainstem response (ABR) is an evoked potential that reflects the responses to sound by brainstem neural centers. The binaural interaction component (BIC) is obtained by subtracting the sum of the monaural ABR responses from the binaural response. Its latency and amplitude change in response to variations in binaural cues. The BIC is thus thought to reflect the activity of binaural nuclei and is used to non-invasively test binaural processing. However, any conclusions are limited by a lack of knowledge of the relevant processes at the level of individual neurons. The aim of this study was to characterize the ABR and BIC in the barn owl, an animal where the ITD-processing neural circuits are known in great detail. We recorded ABR responses to chirps and to 1 and 4 kHz tones from anesthetized barn owls. General characteristics of the barn owl ABR were similar to those observed in other bird species. The most prominent peak of the BIC was associated with nucleus laminaris and is thus likely to reflect the known processes of ITD computation in this nucleus. However, the properties of the BIC were very similar to previously published mammalian data and did not reveal any specific diagnostic features. For example, the polarity of the BIC was negative, which indicates a smaller response to binaural stimulation than predicted by the sum of monaural responses. This is contrary to previous predictions for an excitatory-excitatory system such as nucleus laminaris. Similarly, the change in BIC latency with varying ITD was not distinguishable from mammalian data. Contrary to previous predictions, this behavior appears unrelated to the known underlying neural delay-line circuitry. In conclusion, the generation of the BIC is currently inadequately understood and common assumptions about the BIC need to be reconsidered when interpreting such measurements.

A mobile sound localization setup

In this paper, a mobile sound localization setup is described that can be used to measure a persons' localization performance in a sophisticated way. With this mobile setup, researchers can travel to subjects, and studies are not limited by the willingness of participants to visit the clinic. In the setup, sounds are presented within a partial sphere in both the horizontal (-70° to 70° azimuth) and vertical (-35° to 40° elevation) plane. Participants are asked to indicate the perceived sound origin by pointing with a head-mounted LED. Head movements are recorded and instantly visualized (i.e. online target response plots). Depending on the research question, the setup can be adjusted for more advanced or simplified measurements, making the setup suitable for a wide range of research questions. The rationale for building this mobile setup was to test horizontal sound localization abilities (binaural hearing) and vertical sound localization abilities (monaural hearing) of children and patients who were otherwise not accessible for testing. In this setup loudspeakers are not visible and subjects are asked to indicate the perceived sound direction by a natural head-pointing response towards the perceived location. An advantage of the implemented pointing-method is the playful manner in which children are tested. They are 'shooting' at the perceived sound target location with a head-mounted LED and have fun while performing the test. •We present a mobile sound localization setup suitable for measuring horizontal and vertical sound localization in children and adult patients in the convenience of their own environment.

Neuroethology of auditory systems: contributions in memory of Albert S. Feng

Albert (Al) S. Feng (1944 - 1921) was a pioneer in the area of neuroethology of auditory systems. This special issue of the Journal of Comparative Physiology A commemorates his life and work by presenting 15 articles written by friends, students, and colleagues, many of whom have become leading experts themselves in this field. Their contributions not only provide a comprehensive overview of bioacoustics in amphibians and mammals (including bats), but also are intended to inspire a new generation of scientists to advance our understanding of brain mechanisms of acoustic perception.

Differential advantages of musical backgrounds on binaural integration and interaction skills in instrumentalists, vocalists, and non-musicians

Background

Musical perception requires a host of skills. Instrumental musicians place greater emphasis on motor coordination, whereas vocal musicians rehearse vocal sounds. The study explored the differential advantages of musical background on binaural integration and interaction in musicians (instrumentalists, vocalists) and compared them with age-matched non-musicians.

Methods

Eight six participants aged 20-40 y with normal hearing sensitivity were subjected to binaural tests using a standard group comparison research design. The participants were segregated into three groups - Group 1 included instrumentalists (n = 26, mean age: 17.73 ± 2.83 y), while Group 2 and Group 3 consisted of vocalists (n = 30, mean age: 19.30 ± 2.47 y) and non-musicians (n = 30, mean age: 18.20 ± 3.02 y) respectively. The binaural processes namely integration (Dichotic syllable test, DST; and virtual acoustic space identification - VASI) and interaction (Interaural difference thresholds for time and level: ITD & ILD), were administered on all the participants.

Results

Statistical analyses showed the main effect of musicianship. Bonferroni pair-wise test revealed that the musicians (instrumentalists and vocalists) outperformed (p < 0.05) non-musicians in all the tests. The differential advantage of the musical background was seen on the binaural integration test with instrumentalists performing better in the VASI test compared to vocalists, and vice-versa for DST. No difference was observed in interaction tasks (ITD & ILD) between vocalists and instrumentalists (p > 0.05).

Conclusion

Musical background-induced differential advantages can be reasonably noted in the binaural skills of instrumentalists and vocalists (compared to non-musicians).

Different binaural processing of the envelope component and the temporal fine structure component of a narrowband noise in rat inferior colliculus

Complex broadband sounds are decomposed by peripheral auditory filters into a series of relatively narrowband signals, each with a slowly varying envelope (ENV) and a rapidly fluctuating temporal fine structure (TFS). ENV and TFS information at the bilateral ears contribute differentially to auditory perception. However, whether the difference could attribute to mechanisms of binaural integration remains an open question. As a potential neural correlate, subsets of neurons in the central nucleus of the inferior colliculus (ICC) are known to integrate binaural information with binaural inhibition or binaural summation. Therefore, we recorded the frequency-following responses (FFRs) to the ENV and TFS components of narrowband noises in the ICC of anesthetized rats and examined changes in FFR amplitude and stimulus-response coherence under various sound-delivery settings. We showed that binaural FFR_ENV was predominantly elicited by contralateral inputs and inhibited by ipsilateral inputs, exhibiting a "binaural-inhibition" like property. On the other hand, binaural FFR_TFS received a balanced contribution from both sides, echoing the "binaural-summation" mechanism. What is more, binaural FFR_ENV was significantly correlated with contralateral-evoked but not ipsilateral-evoked FFR_ENV, while binaural FFR_TFS correlated with both contralateral- and ipsilateral-evoked FFR_TFS. Overall, these results suggest distinct binaural processing of ENV and TFS information at the midbrain level.