Psychoakustik & experimentelle Audiologie - Laufende Projekte

Selective hearing refers to the ability of the human auditory system to selectively attend to a desired speaker while ignoring undesired, concurrent speakers. This is often referred to as the cocktail-party problem. In normal hearing, selective hearing is remarkably powerful. However, in so-called electric hearing, i.e., hearing with cochlear implants (CIs), selective hearing is severely degraded, close to not present at all. CIs are commonly used for treatment of severe-to-profound hearing loss or deafness because they provide good speech understanding in quiet. The reasons for the deficits in selective hearing are mainly twofold. First, they arise from structural limitations of current CI electrode designs which severely limit the spectral resolution. Second, they arise from a lack of salient timing cues, most importantly interaural time difference (ITD) and temporal pitch. The second limitation is assumed to be partly “software”-sided and conquerable with perception-driven signal processing. Yet, success achieved so far is at best moderate.

A recently proposed approach to provide precise ITD and temporal-pitch cues in addition to speech understanding is to insert extra pulses with short inter-pulse intervals (so-called SIPI pulses) into periodic high-rate pulse trains. Results gathered so far in our previous project ITD PsyPhy in single-electrode configurations are encouraging in that both ITD and temporal-pitch sensitivity improved when SIPI pulses were inserted at the signals’ temporal-envelope peaks. Building on those results, this project aims to answer the most urgent research questions towards determining whether the SIPI approach improves selective hearing in CI listeners: Does the SIPI benefit translate into multi-electrode configurations? Does the multi-electrode SIPI approach harm speech understanding? Does the multi-electrode SIPI approach improve speech-in-speech understanding?

Psychophysical experiments with CI listeners are planned to examine the research questions. To ensure high temporal precision and stimulus control, clinical CI signal processors will be bypassed by using a laboratory stimulation system directly connecting the CIs with a laboratory computer. The results are expected to shed light on parts of both electric and acoustic hearing that are still not fully understood to date, such as the role and the potential of temporal cues in selective hearing.


References from our Lab:

Duration: May 2020 - April 2022

Funding: DOC Fellowship Program of the Austrian Academy of Sciences (A-25606)

PI: Martin Lindenbeck

Supervisors: Bernhard Laback and Ulrich Ansorge (University of Vienna)

See also:

Stellen Sie sich vor, Sie befinden sich im dichten Straßenverkehr, inmitten von Fußgängern, Radfahrern und Autos, die sich alle in unterschiedliche Richtungen bewegen. In dieser und vielen anderen Situationen ist es überlebenswichtig, genau zu wissen wo und wann Ereignisse in unserer Umgebung stattfinden. Um möglichst schnell und korrekt auf externe Reize zu reagieren, erzeugt unser Gehirn dabei ständig Vorhersagen über zukünftige Ereignisse. Zum Beispiel, wo ein heranfahrendes Auto sich zu dem Zeitpunkt befinden wird, wenn wir die Straße überqueren wollen. Nicht nur für uns Menschen sind diese Vorhersagen zentral. Auch andere Primaten könnten ähnliche Mechanismen verwenden, etwa wenn sie sich durch dichtes Dschungelgebiet bewegen. Inwiefern die Evolution diese Mechanismen bei Menschen im Vergleich zu anderen Spezies geformt hat, ist bis heute unklar.

Des Weiteren sind unsere Sinnesinformationen oft mehrdeutig, sodass unser Gehirn mehrere parallele Interpretationen und Vorhersagen erzeugt und sich letztlich auf eine festlegen muss. Gegenwärtig stammt der Großteil unseres Wissens über diese Wahrnehmungsprozesse aus Studien zum Sehsinn. Vergleichsweise wenig ist darüber für unseren Hörsinn bekannt, welcher aber gleichermaßen zentral für unser Überleben und Sozialverhalten ist.

Das Zukunftskolleg Dynamates möchte diese zentralen Wissenslücken zur Hörwahrnehmung schließen indem es die Vorhersagemechanismen nahe verwandter Spezies in realistischen aber hochkontrollierbaren virtuellen akustischen Umgebungen testen und mit Computermodellen abbilden wird. Zusätzlich wird Dynamates mittels hochauflösender Elektroenzephalographie (EEG) bei Menschen die neuronalen Grundlagen der zugrunde liegenden Prozesse untersuchen. Das Projekt basiert damit auf einer interdisziplinären Zusammenarbeit zwischen ExpertInnen aus dem Bereich der Computermodellierung (Robert Baumgartner), der Neurowissenschaft (Ulrich Pomper), und der Kognitionsbiologie (Michelle Spierings).

Dynamates wird somit den ersten systematischen Vergleich von dynamischen Vorhersage- und Entscheidungsprozessen des Hörsinns zwischen Menschen und nicht-menschlichen Primaten durchführen. Ein besseres Verständnis der neuronalen Grundlagen dieser Prozesse kann Anwendung bei der Behandlung von Personen mit Störungen im Wahrnehmungs- und Entscheidungsverhalten (z.B. bei Autismus oder Schizophrenie) finden. Die erstellten mathematischen Modelle lassen sich in Zukunft auch in anderen Spezies oder bei komplexeren Entscheidungsprozessen (z.B. in sozialen Interaktionen) testen, und können direkte Anwendung in der Entwicklung von künstlicher Intelligenz und virtuellen Realitäten finden.

The auditory system constantly monitors the environment to protect us from harmful events such as collisions with approaching objects. Auditory looming bias is an astoundingly fast perceptual bias favoring approaching compared to receding auditory motion and was demonstrated behaviorally even in infants of four months in age. The role of learning in developing this perceptual bias and its underlying mechanisms are yet to be investigated. Supervised learning and statistical learning are the two distinct mechanisms enabling neural plasticity. In the auditory system, statistical learning refers to the implicit ability to extract and represent regularities, such as frequently occurring sound patterns or frequent acoustic transitions, with or without attention while supervised learning refers to the ability to attentively encode auditory events based on explicit feedback. It is currently unclear how these two mechanisms are involved in learning auditory spatial cues at different stages of life. While newborns already possess basic skills of spatial hearing, adults are still able to adapt to changing circumstances such as modifications of spectral-shape cues. Spectral-shape cues are naturally induced when the complex geometry especially of the human pinna shapes the spectrum of an incoming sound depending on its source location. Auditory stimuli lacking familiarized spectral-shape cues are often perceived to originate from inside the head instead of perceiving them as naturally external sound sources. Changes in the salience or familiarity of spectral-shape cues can thus be used to elicit auditory looming bias. The importance of spectral-shape cues for both auditory looming bias and auditory plasticity makes it ideal for studying them together.

Born2Hear project overview

Born2Hear will combine auditory psychophysics and neurophysiological measures in order to 1) identify auditory cognitive subsystems underlying auditory looming bias, 2) investigate principle cortical mechanisms for statistical and supervised learning of auditory spatial cues, and 3) reveal cognitive and neural mechanisms of auditory plasticity across the human lifespan. These general research questions will be addressed within three studies. Study 1 will investigate the differences in the bottom-up processing of different spatial cues and the top-down attention effects on auditory looming bias by analyzing functional interactions between brain regions in young adults and then test in newborns whether these functional interactions are innate. Study 2 will investigate the cognitive and neural mechanisms of supervised learning of spectral-shape cues in young and older adults based on an individualized perceptual training on sound source localization. Study 3 will focus on the cognitive and neural mechanisms of statistical learning of spectral-shape cues in infants as well as young and older adults.

Key publication: Baumgartner, R., Reed, D.K., Tóth, B., Best, V., Majdak, P., Colburn H.S., Shinn-Cunningham B. (2017): Asymmetries in behavioral and neural responses to spectral cues demonstrate the generality of auditory looming bias, in: Proceedings of the National Academy of Sciences of the USA 114, 9743-9748

Project investigator (PI): Robert Baumgartner

Project partner / Co-PI: Brigitta Tóth, Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary

Collaboration partners:

Duration: April 2020 - March 2024

Supported by the Austrian Science Fund (FWF, I 4294-B) and NKFIH.

Reweighting of Binaural Cues: Generalizability and Applications in Cochlear Implant Listening

Normal-hearing (NH) listeners use two binaural cues, the interaural time difference (ITD) and the interaural level difference (ILD), for sound localization in the horizontal plane. They apply frequency-dependent weights when combining them to determine the perceived azimuth of a sound source. Cochlear implant (CI) listeners, however, rely almost entirely on ILDs. This is partly due to the properties of current envelope-based CI-systems, which do not explicitly encode carrier ITDs. However, even if they are artificially conveyed via a research system, CI listeners perform worse on average than NH listeners. Since current CI-systems do not reliably convey ITD information, CI listeners might learn to ignore ITDs and focus on ILDs instead. A recent study in our lab provided first evidence that such reweighting of binaural cues is possible in NH listeners.

This project aims to further investigate the phenomenon: First, we will test whether a changed ITD/ILD weighting will generalize to different frequency regions. Second, the effect of ITD/ILD reweighting on spatial release from speech-on-speech masking will be investigated, as listeners benefit particularly from ITDs in such tasks. And third, we will test, whether CI listeners can also be trained to weight ITDs more strongly and whether that translates to an increase in ITD sensitivity. Additionally, we will explore and evaluate different training methods to induce ITD/ILD reweighting.

The results are expected to shed further light on the plasticity of the binaural auditory system in acoustic and electric hearing.

Start: October 2018

Duration: 3 years

Funding: uni:docs fellowship program for doctoral candidates of the University of Vienna

Objective and Methods:

This project cluster includes several studies on the perception of interaural time differences (ITD) in cochlear implant (CI), hearing impaired (HI), and normal hearing (NH) listeners. Studying different groups of listeners allows for identification of the factors that are most important to ITD perception. Furthermore, the comparison between the groups allows for the development of strategies to improve ITD sensitivity in CI and HI listeners.

Subprojects:

  • FsGd: Effects of ITD in Ongoing, Onset, and Offset in Cochlear Implant Listeners
  • ITD Sync: Effects of interaural time difference in fine structure and envelope on lateral discrimination in electric hearing
  • ITD Jitter CI: Recovery from binaural adaptation with cochlear implants
  • ITD Jitter NH: Recovery from binaural adaptation in normal hearing
  • ITD Jitter HI: Recovery from binaural adaptation with sensorineural hearing impairment
  • ITD CF: Effect of center frequency and rate on the sensitivity to interaural delay in high-frequency click trains
  • IID-CI: Perception of Interaural Intensity Differences by Cochlear Implant Listeners

   

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Bilateral Cochlear Implants: Physiology and Psychophysics

Current cochlear implants (CIs) are very successful in restoring speech understanding in individuals with profound or complete hearing loss by electrically stimulating the auditory nerve. However, the ability of CI users to localize sound sources and to understand speech in complex listening situations, e.g. with interfering speakers, is dramatically reduced as compared to normal (acoustically) hearing listeners. From acoustic hearing studies it is known that interaural time difference (ITD) cues are essential for sound localization and speech understanding in noise. Users of current bilateral CI systems are, however, rather limited in their ability to perceive salient ITDs cues. One particular problem is that their ITD sensitivity is especially low when stimulating at relatively high pulses rates which are required for proper encoding of speech signals.  

In this project we combine psychophysical studies in human bilaterally implanted listeners and physiological studies in bilaterally implanted animals to find ways in order to improve ITD sensitivity in electric hearing. We build on the previous finding that ITD sensitivity can be enhanced by introducing temporal jitter (Laback and Majdak, 2008) or short inter-pulse intervals (Hancock et al., 2012) in high-rate pulse sequences. Physiological experiments, performed at the Eaton-Peabody Laboratories Neural Coding Group (Massachusetts Eye and Ear Infirmary, Harvard Medical School, PI: Bertrand Delgutte), are combined with matched psychoacoustic experiments, performed at the EAP group of ARI (PI: Bernhard Laback). The main project milestones are the following:

·         Aim 1: Effects of auditory deprivation and electric stimulation through CI on neural ITD sensitivity. In physiological experiments it is studied if chronic CI stimulation can reverse the effect of neonatal deafness on neural ITD sensitivity.

·         Aim 2: Improving the delivery of ITD information with high-rate strategies for CI processors.

   A. Improving ITD sensitivity at high pulse rates by introducing short inter-pulse intervals

   B. Using short inter-pulse intervals to enhance ITD sensitivity with “pseudo-syllable” stimuli.

Co-operation partners:

·         External: Eaton-Peabody Laboratories Neural Coding Group des Massachusetts Eye and Ear Infirmary an der Harvard Medical School (PI: Bertrand Delgutte)

·         Internal: Mathematik und Signalverarbeitung in der Akustik

Funding:

·      This project is funded by the National Institute of Health (NIH). http://grantome.com/grant/NIH/R01-DC005775-11A1

·      It is planned to run from 2014 to 2019.

Press information:

·      Article in DER STANDARD: http://derstandard.at/2000006635467/OeAW-und-Harvard-Medical-School-forschenCochleaimplantaten

·      Article in DIE PRESSE: http://diepresse.com/home/science/3893396/Eine-Prothese-die-in-der-Horschnecke-sitzt

·      OEAW website: http://www.oeaw.ac.at/oesterreichische-akademie-der-wissenschaften/news/article/transatlantische-hoerhilfe/

Publications

See Also

ITD MultEl

ITD MultEl: Binaural-Timing Sensitivity in Multi-Electrode Stimulation

Binaural hearing is extremely important in everyday life, most notably for sound localization and for understanding speech embedded in competing sound sources (e.g., other speech sources). While bilateral implantation has been shown to provide cochlear implant (CIs) listeners with some basic left/right localization ability, the performance with current CI systems is clearly reduced compared to normal hearing. Moreover, the binaural advantage in speech understanding in noise has been shown to be mediated mainly by the better-ear effect, while there is only very little binaural unmasking.

There exists now a body of literature on binaural sensitivity of CI listeners stimulated at a single interaural electrode pair. However, the CI listener’s sensitivity to binaural cues under more realistic conditions, i.e., with stimulation at multiple electrodes, has not been systematically addressed in depth so far.

This project attempts to fill this gap. In particular, given the high perceptual importance of ITDs, this project focuses on the systematic investigation of the sensitivity to ITD under various conditions of multi-electrode stimulation, including interference from neighboring channels, integration of ITD information across channels, and the perceptually tolerable room for degradations of binaural timing information.

Involved people:

Start: January 2013

Duration: 3 years

Funding: MED-EL

Objective:

Bilateral use of current cochlear implant (CI) systems allows for the localization of sound sources in the left-right dimension. However, localization in the front-back and up-down dimensions (within the so-called sagittal planes) is restricted as a result of insufficient transmission of the relevant information.

Method:

In normal hearing listeners, localization within the sagittal planes is mediated when the pinna (outer ear) evaluates the spectral coloring of incoming waveforms at higher frequencies. Current CI systems do not provide these so-called pinna cues (or spectral cues), because of behind-the-ear microphone placement and the processor's limited analysis-frequency range.

While these technical limitations are relatively manageable, some fundamental questions arise:

  • What is the minimum number of channels required to encode the pinna cues relevant to vertical plane localization?
  • To what extent can CI listeners learn to localize sound sources using pinna cues that are mapped to tonotopic regions associated with lower characteristic frequencies (according to the position of typically implanted electrodes)?
  • Which modifications of stimulation strategies are required to facilitate the localization of sound sources for CI listeners?

Application:

The improvement of sound source localization in the front-back dimension is regarded as an important aspect in daily traffic safety.

Funding:

FWF (Austrian Science Fund): Project #P18401-B15

Status:

Finished in Sept. 2010

Subprojects:

  • ElecRang: Effects of upper-frequency boundary and spectral warping on speech intelligibility in electrical stimulation
  • SpecSens: Sensitivity to spectral peaks and notches
  • Loca-BtE-CI: Localization with behind-the-ear microphones
  • Loca Methods: Pointer method for localizing sound sources
  • Loca#Channels: Number of channels required for median place localization
  • SpatStrat: Development and evaluation of a spatialization strategy for cochlear implants
  • HRTF-Sim: Numerical simulation of HRTFs

Localization of sound sources is an important task of the human auditory system and much research effort has been put into the development of audio devices for virtual acoustics, i.e. the reproduction of spatial sounds via headphones. Even though the process of sound localization is not completely understood yet, it is possible to simulate spatial sounds via headphones by using head-related transfer functions (HRTFs). HRTFs describe the filtering of the incoming sound due to head, torso and particularly the pinna and thus they strongly depend on the particular details in the listener's geometry. In general, for realistic spatial-sound reproduction via headphones, the individual HRTFs must be measured. As of 2012, the available HRTF acquisition methods were acoustic measurements: a technically-complex process, involving placing microphones into the listener's ears, and lasting for tens of minutes.

In LocaPhoto, we were working on an easily accessible method to acquire and evaluate listener-specific HRTFs. The idea was to numerically calculate HRTFs based on a geometrical representation of the listener (3-D mesh) obtained from 2-D photos by means of photogrammetric reconstruction.

As a result, we have developed a software package for numerical HRTF calculations, a method for geometry acquisition, and models able to evaluate HRTFs in terms of broadband ITDs and sagittal-plane sound localization performance.

 

Further information:

http://www.kfs.oeaw.ac.at/LocaPhoto

 

Objective:

Bilateral use of current cochlear implant (CI) systems allows for the localization of sound sources in the left-right dimension. However, localization in the front-back and up-down dimensions (within the so-called sagittal planes) is restricted as a result of insufficient transmission of the relevant information.