The Vibrant Soundbridge® middle ear implant: A historical overview

OBJECTIVE

To present a historical overview of the Vibrant Soundbridge^® (VSB) middle ear implant (MEI), since its beginning in the 1990s to date and to describe its course and contemplate what it might become in the future.

HISTORY

MEIs started to take form in researchers' mind in the 1930s with the first experiment of Wilska. In the 1970s, several devices, such as the Goode and Perkins', the Maniglia's, or the Hough and Dormer's were created but remained prototypes. It is only in the 1990s the devices that emerged remained on the market. In 1994, Symphonix, Inc. was created and aimed to manufacture and commercialize its semi-implantable MEI, the VSB. The principle of the VSB lies on a direct drive of the sound to a vibratory structure of the middle ear through an electromagnetic transducer, the floating mass transducer (FMT). The particularity of the system VSB is the simplicity of the transducer which is made of both the magnet and the coil; thus, the FMT, fixed on a vibrating middle ear structure, mimics the natural movement of the ossicular chain by moving in the same direction. The goal of the VSB was to give an alternative to patients with mild-to-severe sensorineural hearing loss who could not wear hearing aids (HAs) or who were unsatisfied conventional HA users. Subsequent to Tjellström's experiment in 1997, implantations started to include etiologies such as otosclerosis, radical mastoidectomy, failed ossiculoplasty/tympanoplasty, and atresia. Nowadays, the VSB, with more than 20 years of experience, is the oldest and most used middle ear implant worldwide. It is well acknowledged that the straightforward design and reliability of the transducer have certainly contributed to the success of the device.

A fractal approach to normal and pathological voices

Using the box-counting method, we demonstrated recently that the stationary signal of vowels is not fractal, but provides the opportunity to design in the smallest scale a kind of signature for each vowel. This fractal approach to these components of speech allows us to quantify the roughness of the voice, between I (sinusoidal complex signal) and 2 (white noise). We used this method to compare these values in normal and pathological voices. We studied the speech of 10 normal speakers, 6 patients suffering from unilateral vocal fold palsy and 6 suffering from various other dysphonias. The meaning of this fractal measurement is discussed and compared with electroglottogram and spectrographic analysis.

A study of speech fractal dimensions

The fractal dimension (D) of a signal gives an estimate of its degree of freedom, which allows estimation of its fluctuations. Using 16 kHz time sampling and the box counting method we studied the Ds of some of the main stationary parts of French speech, the phonemes [a], [e], [i], [o], [y], pronounced 4 times by 10 males and 10 females. Our study demonstrated that the stationary signal of vowels is not fractal, but may, at the smallest scale, provide a kind of signature for each vowel, though the present categorization is not totally significant. Since the box counting method objectifies and quantifies the roughness of the signal, this procedure may be useful for clinical applications. In case of dysphonia, moreover, these signatures could be perhaps be included in the speech signal processing of cochlear implants.

Asynchronous interleaved stimulation (AIS): a new speech coding strategy for cochlear implant

Cochlear implants use a fixed or F0 dependent stimulation rate, whatever the sound analysed (vowel or consonant) or procedure (fixed filters or FFT). We present a procedure which varies as a function of the input signal. This method is based on FFT analysis using a variable width analysis window. Short windows are applied on the transient part of the signal, providing poor frequency resolution but good time resolution; they permit us to accurately follow the speech signal in time during its fast temporal variations. Large windows are applied on the stationary parts of the signal, providing better frequency resolution but poor time resolution. Transient parts of the speech order this window switching; they are detected using the statistical properties of the FFT; moreover, the narrow windowing is coupled to an increase of the stimulation frequency. This strategy has been implemented using the DIGISONIC cochlear implant software, and clinically assessed in 6 regular cochlear implant users, on the basis of a consonant-vowel-consonant test. This Asynchronous-Interleaved-Stimulation (AIS) strategy provides the patients with better discrimination than fixed window FFT analysis. The coding protocol will be described and results presented.