Annual Report 1999
Table of Contents
The long-term goal of research in Hearing Technology is to understand
- how the physiological state of the human auditory system affects the
ability to detect and analyse sound,
- how an impaired ability to detect and analyse sound affects the ability
to understand and produce speech,
- how personal aids should be designed and individually fitted to compensate
for hearing impairment.
The group pursues several applied projects concerning the design, fitting,
and evaluation of personal aids for the hearing impaired, as well as methods and systems for teaching and training
of speech perception and speech production.
Multi-modal Sensory Aids
Together with researchers in the speech group we are investigating a
new method to support audio-visual telephone communication for hearing-impaired persons without special equipment
for transmitting video information. The aim of this work is to generate an artificial talking face which can be
used as a lip-reading support by the hearing-impaired telephone user. The articulation movements of the artificial
face are controlled by parameters automatically derived from the speech signal. The control parameters will inevitably
contain some errors caused by the automatic recognition system, and the critical question was whether the artificial
face would still contribute to improve speech perception. Speech recognition tests with hearing-impaired listeners
have now demonstrated that the artificial face can in fact contribute significantly, even when controlled by an
imperfect recognition system which can probably be further improved in future work.
Evaluation of Cochlear Implants
The work on comparing results from conventional hearing aids and cochlear
implants has been continued. The test battery includes measurement of time resolution, auditory, visual and audiovisual
perception of consonants, vowels, prosodic features and speech tracking, as well as subjective assessment. The
aim of the study is to obtain data to support criteria for patient selection for cochlear implant operations, and
also to evaluate the relative importance of various speech cues as speech-reading support.
Signal Processing Algorithms for Hearing Instruments
An industry-related project investigates methods to improve the algorithm
by which a digital hearing instrument adapts its characteristics automatically to varying acoustic listening conditions.
A general pattern-recognition approach has been used in this work.
project (LISCOM) within the TIDE-program of the EU aims at improving listening comfort by noise suppression in
hearing instruments and telephones. Our role in this project has been mainly to evaluate two different algorithms
in various noise backgrounds. Laboratory test results indicate that it is possible to substantially reduce the
subjective loudness of noise, but the speech intelligibility does not improve correspondingly. The psycho-acoustic
evaluation methods developed within this project will also be used in other research.
Individual Fitting of Advanced Hearing Instruments
Several methods for computer-aided fitting of advanced (digital) hearing
aids are being evaluated in a joint project including laboratory and clinical studies in Stockholm and in Lund/Kristianstad.
Preliminary results have shown that different prescriptive methods, proposed in the scientific literature, lead
to widely different recommendations.
A special method for hearing-aid fitting, based on individual tests of
masked short-tone thresholds, has been developed and tested at the hearing clinic at Karolinska hospital in Stockholm.
We have co-operated with this work in order to evaluate some of the effects of basic auditory-signal analysis on
speech recognition. This fitting method is also evaluated in the clinical study in Lund/Kristianstad.
We are also participating in a reference group which aims to standardise
and improve the hearing-aid fitting methods used in Swedish hearing clinics. This work has resulted in a manuscript
for a textbook on hearing-aid fitting, which is intended for use in the education of clinical audiologists. The
book will appear in print in the year 2000.
Teaching and Training Systems
We participate in an EU project (SPECO), developing a new audio-visual
pronunciation teaching and training method and software system for speech- and hearing-impaired children. The basic
part is a general language-independent measuring system and database editor. The database editor makes it possible
to construct modules for all participant languages; these are English, Swedish, Slovenian and Hungarian. Two support
systems are under development for its construction in all languages, one of them being for teaching and training
vowels and the other for fricatives and affricates.