Wednesday, 22 January 2014
Wednesday, 15 January 2014
Thursday, 9 January 2014
Uitnodiging 20 jaar cochleaire implantatie (CI) in UZ Leuven (25 februari 2014)
Op 25 februari 2014 vieren we 20 jaar Cochleaire
Implantatie (CI) in UZLeuven. Het CIteam organiseert een
informatieavond met een lezing door prof dr C. Desloovere en
getuigenissen van een ouder en van een volwassene, gevolgd door een
receptie met infostand.
Meer info via
http://www.uzleuven.be/ci
Thursday, 2 January 2014
PhD Thesis: Improving binaural hearing with cochlear implants and hearing aids (December 2013)
Summary:
Worldwide over 200.000 profoundly deaf people have been implanted with a cochlear implant (CI). A CI directly simulates the auditory nerve fibers by means of electrical pulses, in order to partially restore the hearing. Due to the success of CIs, implantation criteria have been relaxed. As a result, an increasing number of people receiving a CI still has residual hearing in the other ear.
Users of a CI with residual hearing in the non-implanted ear can benefit from using a hearing aid (HA) in this ear. The combined use of a CI and a HA in the contralateral ear is called bimodal stimulation. Although bimodal listeners receive binaural input of sound, they show poor speech understanding in noise and sound localization abilities. This is partly caused by the fact that current clinical CIs and HAs were not designed to work together. The independent fitting and processing of the devices as well as differences in the way the sound is transmitted in both ears, limit the ability of bimodal listeners in using binaural information. Binaural cues such as the interaural time difference (ITD) and the interaural level difference (ILD) are the basic cues for sound localization and contribute to speech understanding in noise. Previously, it has been shown that bimodal listeners can be sensitive to ITDs and ILDs in simple narrow band stimuli. In order to improve localization performance for bimodal listeners, there is a need for optimized signal processing to improve the perception of binaural cues through their clinical devices.
In the first part of this PhD thesis, multiple studies were performed with the aim to further characterize ITD perception with bimodal stimulation using more realistic stimuli. Using these results, in the second part of this thesis a sound processing strategy, the modulation enhancement strategy (MEnS), was developed to improve ITD perception with bimodal stimulation. MEnS enhances modulations in the electric signal, synchronously with modulations in the acoustic signal presented to the non-implanted ear, based on measurement of the peaks occurring at the rate of the fundamental frequency in voiced speech. The modulations are provided synchronous across electrode channels. JNDs in ITD were determined for five bimodal listeners using an artificial vowel processed by either the clinical standard speech processing strategy (ACE) or MEnS. All subjects were sensitive to ITD with MEnS. With MEnS, performance was significantly better for all subjects and within the range of physically available ITDs.
The results are encouraging and suggest that the concept of enhancing modulations at the CI side is promising for the improvement of ITD perception with bimodal stimulation. Improved perception of binaural cues could lead to better localization performance and speech understanding in noise.
Overall the studies described in this thesis provide valuable new information with regard to the characterization of ITD sensitivity with bimodal stimulation and provide an important step towards the development of a binaural strategy for bimodal stimulation.
For further information the phd thesis is available through the following link: thesis.pdf
Worldwide over 200.000 profoundly deaf people have been implanted with a cochlear implant (CI). A CI directly simulates the auditory nerve fibers by means of electrical pulses, in order to partially restore the hearing. Due to the success of CIs, implantation criteria have been relaxed. As a result, an increasing number of people receiving a CI still has residual hearing in the other ear.
Users of a CI with residual hearing in the non-implanted ear can benefit from using a hearing aid (HA) in this ear. The combined use of a CI and a HA in the contralateral ear is called bimodal stimulation. Although bimodal listeners receive binaural input of sound, they show poor speech understanding in noise and sound localization abilities. This is partly caused by the fact that current clinical CIs and HAs were not designed to work together. The independent fitting and processing of the devices as well as differences in the way the sound is transmitted in both ears, limit the ability of bimodal listeners in using binaural information. Binaural cues such as the interaural time difference (ITD) and the interaural level difference (ILD) are the basic cues for sound localization and contribute to speech understanding in noise. Previously, it has been shown that bimodal listeners can be sensitive to ITDs and ILDs in simple narrow band stimuli. In order to improve localization performance for bimodal listeners, there is a need for optimized signal processing to improve the perception of binaural cues through their clinical devices.
In the first part of this PhD thesis, multiple studies were performed with the aim to further characterize ITD perception with bimodal stimulation using more realistic stimuli. Using these results, in the second part of this thesis a sound processing strategy, the modulation enhancement strategy (MEnS), was developed to improve ITD perception with bimodal stimulation. MEnS enhances modulations in the electric signal, synchronously with modulations in the acoustic signal presented to the non-implanted ear, based on measurement of the peaks occurring at the rate of the fundamental frequency in voiced speech. The modulations are provided synchronous across electrode channels. JNDs in ITD were determined for five bimodal listeners using an artificial vowel processed by either the clinical standard speech processing strategy (ACE) or MEnS. All subjects were sensitive to ITD with MEnS. With MEnS, performance was significantly better for all subjects and within the range of physically available ITDs.
The results are encouraging and suggest that the concept of enhancing modulations at the CI side is promising for the improvement of ITD perception with bimodal stimulation. Improved perception of binaural cues could lead to better localization performance and speech understanding in noise.
Overall the studies described in this thesis provide valuable new information with regard to the characterization of ITD sensitivity with bimodal stimulation and provide an important step towards the development of a binaural strategy for bimodal stimulation.
For further information the phd thesis is available through the following link: thesis.pdf
Monday, 30 December 2013
Friday, 13 December 2013
Technical Comparison Sennheiser HDA 200/300
In our lab, the Sennheiser HDA 200 headphones are widely used for anything audiology related. They are pleasant to wear for a long time, have a flat frequency response and high passive ambient noise attenuation as they are based on PELTOR hearing protectors.
Sadly, these headphones went out of production. And according to Sennheiser, there is no way that they will resume production. Instead, they recommended their designated successor headphones, the Sennheiser HDA 300.
Sadly, these headphones went out of production. And according to Sennheiser, there is no way that they will resume production. Instead, they recommended their designated successor headphones, the Sennheiser HDA 300.
Official technical information
For both headphones, technical data sheets with information on passive attenuation and sensitivity level (frequency response) are available from the Sennheiser website (HDA 200, HDA 300).
For passive attenuation above 250 Hz, the HDA 300 is worse than the HDA 200, with an average difference of 16 dB for the frequencies range from 500 Hz to 8 kHz.
For the flatness of the sensitivity level, the profile of the HDA 300 has a standard deviation of 9 dB (octave frequencies 125 Hz to 16 kHz), which is nearly twice as much as the 5 dB for the HDA 200.
The HDA 300 headphones weight 490 g, an increase of 50 % over the 330 g of the HDA 200. The transducer impedance of 40 Ohm is reduced to 23 Ohm.
The HDA 300 headphones weight 490 g, an increase of 50 % over the 330 g of the HDA 200. The transducer impedance of 40 Ohm is reduced to 23 Ohm.
Own measurements
We tried to reproduce the data on passive attenuation and sensitivity level for the two types of headphones. The measurements were done in a sound-proof room with a Brüel & Kjær artificial ear 4153, with 4 speakers creating a diffuse noise sound field of about 70 dB(SPL). For the frequency sensitivity measurements, a continuous sweep was used. One side of the headphones was placed on the artificial ear, while the other side was wrapped around a side of the measurement table.
With this setup, we could observe a smaller difference in passive attenuation of 8 dB (octave frequencies 2 to 8 kHz) for frequencies above 2 kHz instead of 500 Hz. For lower frequencies, no difference was found. We suspect that the difference between our measurements and the official Sennheiser data is caused by our less-than-perfect measurement setup, especially the way we fixed the headphone to the artificial ear.
For the sensitivity level, we measured a standard deviation of 3 dB for the HDA 200 and 9 dB for the HDA 300 (octave frequencies 125 Hz to 16 kHz).
tl;dr (Summary)
Compared to the HDA 200, the HDA 300 headphones have less passive attenuation, a worse frequency sensitivity profile and are much heavier. We are not impressed.
Monday, 9 December 2013
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