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Stefan Stenfelt

Research in Technical Audiology

Below is an overview of some of our ongoing research projects.

Hearing diagnostics

It is of great importance to be able to diagnose the hearing in patients that cannot cooperate for various reasons (age, mental status, sedation, legal issues etc).

One promising method is to use ASSR (auditory steady state response) for frequency specific hearing thresholds. However, it is not totally clear how to these thresholds relate to normal standard tone thresholds. Another way to obtain hearing thresholds through neural activation is by brainstem audiometry (BRA).
The classic way to elicit the neural potentials is by acoustic click stimulation. Since a click comprises a broad range of frequency components, the neural activation pattern will be spread in time due to the cochlea’s time-frequency characteristic.
Therefore, by designing a chirp stimulus where all frequency components reach their specific place in the cochlea simultaneously, an increased neural activity can be accomplished providing more secure diagnostics.

In a project at the hearing clinic hearing thresholds obtained with ordinary audiometry, ASSR, and chirp-evoked BRA are measured and compared. The result from this study will be used for future clinical hearing assessment, in adults as well as in children.

In the project: Stefan Stenfelt

Differential diagnostics

A general problem in hearing (re)habilitation is that two persons with seemingly equivalent hearing ability (as measured by the audiogram) can benefit significantly different from the same hearing aid and intervention. The underlying reason is certainly complex but one explanation is that there is no differentiation between different types of inner ear hearing losses. This means that problems with e.g. the outer hair cells are treated similar as problems originating in inner hair cells or stria vascularis.

One way to enable specific diagnostics of the lesion in the cochlea is to devise an anatomical and physiological valid model of the sound to neural transmission in the cochlea. Such a model would provide understanding of the different parts influence of the transmission and to what extent a pathological state affect this transmission. Also, the model would give insight on how to diagnose the different lesions separately. (see Stenfelt, S., 2008, Towards understanding the specifics of cochlear hearing loss – a modeling approach ,Int J Audiol 47:1,S10)

The project is sponsored by the Swedish Research Council through the Linnaeus HEAD excellence center grant

In the project: PhD student Amin Saremi, Stefan Stenfelt, Elina Mäki-Torkko

AIST

Auditory Inference Span Test (AIST) is a test to measure the effort to hear. It is believed that the more effort a person needs for understanding speech, the less capacity is left for other tasks. It can be postulated that if understanding speech is easy a person would score high on a test of storing information and make inferences from the stored information while the score would be low on the same test if the speech is presented in a non-ideal situation. Such test (AIST) is being developed and verified. Its usage is predicted to be valuable for fitting hearing aids as well as evaluating noise reducing or speech enhancing algorithms in hearing aids.

The project is supported by the Oticon Foundation.

In the project: PhD student Niklas Rönnberg, Stefan Stenfelt, Mary Rudner, Thomas Lunner

Speech-based test for children

Speech material is used in Sweden primarily for testing the hearing function and evaluating hearing aid fittings. Today, different types of material exist such as phonemically balanced word lists (PB words), Hageman Sentences and HINT sentences. All these were developed for adults with the exception of the (PB words) where two lists have been recorded. However, these two child PB word lists have only been verified on adults and the words are taken from a national Swedish word database from the 1930ies. Consequently, there is a need of a new and verified audiologic speech material for usage in children.

In this project to develop new speech material for children, spoken word material has been recorded in two age categories of children, 5-6 years old and 7-10 years old. The word recording, transcription, and frequency analysis was conducted by a team of speech and language therapist master students. Currently, the database of normal word usage in these age-groups are expanded and balanced word lists and sentences will be constructed, recorded and verified in a group of children.

The project is supported by Hearing Research foundation

In the project: Stefan Stenfelt

Hearing physiology

Hearing one’s own voice

During 2009, Sabine Reinfeldt defended her thesis where a part was devoted to explore the differences between the air conduction and bone conduction part of one’s own voice. With a basis in those results, the work continues with understanding how fitting of hearing aids alter the perceived own voice in hearing aid users. A model of the sound transmission during own vocalization is used together with models of the occlusion effect and hearing aid characteristics to predict the perceived own voice. The model is currently verified in a clinical sample of hearing aid users.

In the project: Stefan Stenfelt

Stapedius reflex and own voice.
It was shown in the 1970ies that the stapedius muscle was elicited during own vocalization. However, it has never been verified to what extent it affects the perception of the own voice. Moreover, it has never been shown if the stapedius reflex affects sound transmission by air conduction similarly as it does bone conduction. This is investigated by measurement of neural brainstem potentials while eliciting the stapedius muscle and using both air and bone conduction stimulation.

In the project: Stefan Stenfelt

Bone conduction physiology

For an overview, see Stenfelt, S. and Goode, R. L., 2005, Bone conducted sound: Physiological and clinical aspects, Otol. Neurotol. 26, 1245.This is an ongoing project where the aim is to further our understanding of the perception of bone conducted sound. Currently, two areas of bone conduction are investigated. One is the transmission of sound in the human skull bone where measurements using laser Doppler Vibrometer have revealed the physical behaviour of bone conducted sound in the skull (see e.g. Stenfelt, S. and Good R.L., 2005, Transmission properties of bone conducted sound: Measurements in cadaver heads, J. Acoust. Soc. Am. 118(4), 2373 and Eeg-Olofsson, M., Stenfelt, S., Granström, G., Tjellström, A., and Johansson, B. 2008, Transmission of bone conducted sound in the human skull measured by cochlear vibrations, Int. J. Audiol. 47, 761. Another area investigated is the possibility to use binaural cues during bilateral bone conduction stimulation.

The project is supported in part by Stinger foundation

In the project: PhD student Måns Eeg-Olofsson, Stefan Stenfelt

Hearing screening technologies

AHEAD III

Assessment of hearing in the elderly: aging and degeneration - integration through immediate intervention (AHEAD-III) is a coordination action EU project within the seventh framework programme with 19 partners where we are responsible for the work package of new screening technologies. The aim of the project is to (1) provide evidence of the effects of hearing impairments in adults and particularly in the elderly, (2) provide quality standards and minimum requirements for screening methods and related diagnostic techniques, and (3) develop guidelines and recommendations on how to implement successful screening programmes to be tuned to the local, social, and economical conditions of a country. This project started May 1st 2008 and has duration of 36 months.

The project is supported by EU 7th framework grant

In the project: Post Doc Marie Öberg, Stefan Stenfelt

Cognitive hearing Science

These projects are conducted within the framework of Linnaeus HEAD excellence center at Linköping University.

N200

N200 is a large study investigating alternative hypothesis about the human signal-cognition interface (see Stenfelt, S., Rönnberg, J., 2009, The signal-cognition interface: Interactions between degraded auditory signals and cognitive processes, Scand. J. Psychol. 50, 385). The name of the study refers to the number of hearing impaired persons that are being tested. The test-persons are evaluated thoroughly of their hearing abilities (hearing thresholds, DPOAEs, TEN(HL), PB-words) and also tested for hearing in noise using different sentence material (Hageman, HINT) and cognitive abilities using several tests of cognition and working memory. Beside this, executive functions (shifting, updating and inhibition), attention, and meaning extraction will be tested using newly developed tests. This project involves nearly 10 senior researchers with different backgrounds and a couple of PhD students for the execution of the testing and conducting the analysis. We at technical audiology are primarily responsible for the hearing testing and auditory aspects of the new tests.

The project is sponsored by the Swedish Research Council through the Linnaeus HEAD excellence center grant and a grant from the Swedish council for working life and social research.

In the project: Beside Stefan Stenfelt plus some 10 person within Linnaeus Centre HEAD

fMRI

Functional magnetic resonance imaging is a technique enabling the measurement of the haemodynamic response related to neural activity in the brain. It is a valuable tool for investigations of brain activities during auditory input. Unfortunately, image scanning produces high sound pressure levels, exceeding 100 dBA. As a consequence, the sound exposure for a person placed in a MRI scanner is too high, even with state-of-the-art ear defenders, to allow investigations of auditory functions. However, intelligent programming (e.g. sparse imaging) and active noise cancelling techniques have shown promise for using fMRI for auditory research. At present, an investigation is ongoing using the sparse method to obtain functional images of normal hearing subjects’ brains during speech recognition in adverse acoustical conditions. These data will be correlated to the subjects overall cognitive abilities.

The project is sponsored by the Swedish Research Council through the Linnaeus HEAD excellence center grant.

In the project: Stefan Stenfelt, Ingrid Johnsrude, Jerker Rönnberg, Mary Rudner, Örjan Dahlström, Maria Engström

Hearing aids/cochlear implants

Hearing aid evaluation

New hearing aids are constantly introduced to the market. Both the producers and the users are interested in ecological testing of the hearing aids within their target groups. It is therefore a need for testing of these aids in the daily life and evaluates the benefit for hearing aid users. Our lab has the ability to test spatial behavior of hearing aids in a near real-life environment.

Rehabilitation for unilateral deafness

Classically, a unilateral deaf person has been rehabilitated with a contralateral routing of signal (CROS) hearing aid where the sound is recorded by a microphone on the deaf side and transmitted to an earphone positioned in the healthy ear; by that removing the head shadow effect. Since a cable have been used to transmit the signal transcranially and the hearing aid on the good side disrupts the normal hearing, this solution has not been well accepted and many unilateral deaf persons decide to go unaided. A relatively new way of transmitting the sound from the deaf side to the hearing ear is by way of bone conduction using for example the Cochlear BAHA system or Oticon Medical Ponto system. We are currently investigating audiological factors that can be used as predictors in pre-fitting estimations of benefit of different hearing aid systems (normal CROS, bone conduction CROS, or no aid) for subjects with unilateral deafness.

In the project: Stefan Stenfelt, Elina Mäki-Torkko, Henrik Harder

Bilateral cochlear implants in children

In collaboration between Karolinska Institutet and Linköping University, 80 bilaterally implanted cochlear implantees in the ages 5 to 12 years are followed during a two year period. During this time, three test occasions occurs with one year between (initial, after one year, and final after two years). The cochlear implanted children are tested for their ability to hear in a noise background and to localize sound sources monaurally and bilaterally. Also, parental experiences are obtained with questionnaires. Currently, data from the final test occasion are collected.

In the project: PhD student Filip Asp, Stefan Stenfelt, Elina Mäki-Torkko, Eva Karltorp, Leif Hergils, Henrik Harder


 

Stefan Stenfelt
Name: Stefan Stenfelt
Title: Professor
Department: IKE

CONTACT

Phone: +46 (0)10-103 28 56
E-mail: stefan.stenfelt@liu.se

Address:
Linköping University
Department of Clinical and Experimental Medicine
Technical Audiology
S-581 85 Linköping
Sweden
 

Related links

The Brain and The Nervous System


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Last updated: 2014-02-10