[Aspects of voice quality quantification]. / Quantification des aspects qualitatifs de la voix.

The present work is directed towards providing a complement to the current use of sustained sounds as the basis for the physical measurement of voice quality parameters. For many clinical observations, there is a clear lack of correspondence between the measurement results, for example of shimmer, jitter and harmonic to noise ratio, and the perceived quality of the speaking voice. Our work is motivated by the need to overcome this familiar problem. It has four main objectives: to use running speech as the basis for one set of measurements in the clinical protocol; to link physical measures based on the use of this data with both production and perception; to employ voice production data as the foundation for auditorily significant criteria; the presentation of quantitative comparisons using sustained sound and running speech data, derived for a range of pathological voice conditions, within the same clinical session. Our pilot observations are based on the use of clinical acoustic and laryngographic data from patients of 4 different clinical centres.

New developments in speech pattern element hearing aids for the profoundly deaf.

Two new developments in speech pattern processing hearing aids will be described. The first development is the use of compound speech pattern coding. Speech information which is invisible to the lipreader was encoded in terms of three acoustic speech factors; the voice fundamental frequency pattern, coded as a sinusoid, the presence of aperiodic excitation, coded as a low-frequency noise, and the wide-band amplitude envelope, coded by amplitude modulation of the sinusoid and noise signals. Each element of the compound stimulus was individually matched in frequency and intensity to the listener's receptive range. Audio-visual speech receptive assessments in five profoundly hearing-impaired listeners were performed to examine the contributions of adding voiceless and amplitude information to the voice fundamental frequency pattern, and to compare these codings to amplified speech. In both consonant recognition and connected discourse tracking (CDT), all five subjects showed an advantage from the addition of amplitude information to the fundamental frequency pattern. In consonant identification, all five subjects showed further improvements in performance when voiceless speech excitation was additionally encoded together with amplitude information, but this effect was not found in CDT. The addition of voiceless information to voice fundamental frequency information did not improve performance in the absence of amplitude information. Three of the subjects performed significantly better in at least one of the compound speech pattern conditions than with amplified speech, while the other two performed similarly with amplified speech and the best compound speech pattern condition. The three speech pattern elements encoded here may represent a near-optimal basis for an acoustic aid to lipreading for this group of listeners. The second development is the use of a trained multi-layer-perceptron (MLP) pattern classification algorithm as the basis for a robust real-time voice fundamental frequency extractor. This algorithm runs on a low-power digital signal processor which can be incorporated in a wearable hearing aid. Aided lipreading for speech in noise was assessed in the same five profoundly hearing-impaired listeners to compare the benefits of conventional hearing aids with those of an aid which provided MLP-based fundamental frequency information together with speech+noise amplitude information. The MLP-based pattern element aid gave significantly better performance in the reception of consonantal voicing contrasts from speech in pink noise than that achieved with conventional amplification and consequently, it also gave better overall performance in audio-visual consonant identification.(ABSTRACT TRUNCATED AT 400 WORDS)

Psychoacoustic aspects of speech pattern coding for the deaf.

The SiVo aid, which provides a sinusoidal signal indicating voice fundamental frequency and voicing information, was compared as an aid to lipreading to a conventional hearing aid having extended low-frequency output. Speech perceptual measures of consonant confusions in lipreading and the identification of a simple intonation contrast were collected from a group of 8 profoundly deaf adults. Audiometric and psychoacoustic measures were also collected. In the intonation task, 6 of the 7 patients tested performed better with the SiVo aid and the seventh scored perfectly with both aids. Four patients (out of 8) preferred to use the SiVo aid rather than the conventional aid, and 2 of these showed a significant advantage with the SiVo aid in the aided lipreading of consonants. The remaining 4 patients preferred the conventional aid, although none of these patients showed a significant advantage with the conventional aid in the lipreading of consonants. The 4 patients who preferred the SiVo aid over the conventional aid had very profound hearing loss and minimal dynamic range at 500 Hz and above, and those receiving the greatest benefit showed no measurable frequency selectivity. In the 2 patients who preferred the SiVo aid, yet showed no significant advantage for the SiVo aid in consonant lipreading, consonant confusions were also measured for aided lipreading, using a prototype aid providing both voice fundamental frequency and voiceless excitation patterns. Both patients showed additional and significant benefit from inclusion of the voiceless pattern element.

Structural effects of short term and chronic extracochlear electrical stimulation on the guinea pig spiral organ.

To assess the effects of extracochlear electrical stimulation on cochlear structure, guinea pigs were implanted and stimulated with single middle ear electrodes either at round window or promontory sites, and their cochleae examined by transmission electron microscopy. Implanted but unstimulated, or unimplanted control animals were examined in the same way. Alternating current stimulation at the promontory for 2 h at 150 Hz, 500 microA, caused outer hair cell efferent endings to become dense and vacuolated, but no hair cells were damaged. With direct current stimulation at 500 microA for 2 h the basal regions of the stimulated cochlea were badly damaged and many outer hair cells lysed. Long term (up to 1200 h) round window stimulation at 100 or 141 Hz, 15-91 microA rms, did not cause cell death or inner hair cell damage, but basal outer hair cells and their efferent endings were badly affected in both ipsilateral and contralateral cochleae. The compound action potential of the auditory evoked response to broad band click stimuli was not altered by chronic electrical stimulation. It is concluded that chronic stimulation with the parameters used does not threaten cochlear survival, and it is proposed that the bilateral structural changes induced by chronic stimulation are caused by excessive activation of the cochlear efferent pathways.

Structural alteration of hair cells in the contralateral ear resulting from extracochlear electrical stimulation.

Chronic electrical stimulation of the auditory nerve in patients with profound sensori-neural deafness is becoming increasingly routine. Therefore, it is important to understand more about the long-term consequences of this procedure. Hitherto, structural studies in animals after electrocochlear stimulation have concentrated on the stimulated cochlea. Here we have examined the effects of unilateral extracochlear electrical stimulation on the spiral organ of both the ipsilateral and contralateral ears of the mature guinea pig, and have found alterations in the structure of the outer hair cells and their efferent nerve terminals in the contralateral as well as the ipsilateral cochlea. This is the first evidence for a structural influence of efferent activity on the cochlea. Although the importance of the efferent system, consisting of the crossed and uncrossed olivo-cochlear bundles, is well established in providing central control of the sensory pathways, its exact role in hearing is incompletely understood. However, it is known that the outer hair cells and their efferent innervation are important in their contribution to inner hair cell responses and in modulating the micromechanics of the whole cochlea. These efferent functions now appear to be related to an important part of cochlear morphology, and are also relevant to our understanding of cochlear neurobiology, normal development and the management of hearing disability in both adult and child.

Audiological rehabilitation of patients with brainstem disorders.

A brief account is given of the course of rehabilitation of three patients with severe brainstem injuries. Particular use has been made of synthetic speech pattern assessment procedures which have been integrated into the management model of Goldstein and Stephens (1981). The use of speech stimuli of controllable simplicity has two main clinical benefits: the early course of re-acquisition can be examined analytically, second, aspects of speech receptive and productive rehabilitation can be facilitated. Re-acquisition of perceptive ability in some of these patients may follow a progression from simple to complex acoustic pattern contrasts and this may provide an effective basis for future techniques of rehabilitation.

Microprocessor-controlled speech pattern audiometry. Preliminary results.

Interactive microprocessor-controlled speech pattern tests making use of high-quality synthetic speech have been used to assess the development of subjects' ability to process speech contrasts of increasing complexity, from prosodic contrasts to a 'date-gate' place contrast. These tests have been particularly useful in mapping the development or recovery of subjects functioning at the very first stages of processing ability. Some results obtained with profoundly hearing-impaired children and with adults suffering from brain stem disorders are reported, and further applications of speech pattern audiometric techniques are briefly discussed.

Clinical analysis of laryngeal trauma secondary to intubation.

A study was undertaken to analyse the effect of short-term intubation on the voice. Children were examined laryngographically both pre- and postoperatively. Changes in larynx frequency distribution following intubation were documented using the technique of electrolaryngography; the resolution of these changes was similarly recorded. The results, in comparison with the frequency distributions associated with other disease states, give insight into the nature of the damage and its effect on vocal fold vibratory patterns. The technique therefore enables objective evidence of minor degrees of laryngeal trauma to be demonstrated and differentiated.

Speech signal presentation to the totally deaf.

We have developed a system for single-channel electrical stimulation of the totally deaf. The patient wears a removeable electrode assembly which stimulates the cochlear promontory and can be inserted and removed like the earmould of a hearing aid. This approach minimises the risk of mechanical or electro-chemical damage to structures within the cochlea. Charge-balanced stimulation is used to present those speech pattern elements that are matched to the patients' lipreading needs and their new sensory abilities. Objective tests show improvements both in patients' perceptive and productive abilities.

Examination of vocal fold movement by ultra-short pulse X radiography.

Antero-posterior radiographs of the larynx lack spatial and temporal resolution, due to the movement of the vocal folds during phonation. By utilising the electrolaryngograph to monitor vocal fold movement, single X-ray pulses of 30 nanoseconds duration have been triggered at pre-determined points during the cycle of vocal fold movement to visualise these in normal phonation.

Voice pitch as an aid to lipreading.

The totally deafened adult, unable to make use of a hearing aid, has no alternative to lipreading for everyday communication. Lipreading, however, is no substitute for hearing speech. Many lipreaders have great difficulty in ideal conditions and even the best lipreaders find the task demanding and tiring. Prosthetic attempts to substitute for lost hearing have centred on three distinct types of intervention, visual, tactile, and electrocochlear. As none of these is likely to yield a good understanding of a speech independent of lipreading in the near future, we have attempted to isolate relatively simple patterns of stimulation that, although not intelligible in themselves, well aid lipreading. From this point of view, the fundamental frequency or 'pitch' of the voice is the most important pattern element because if provides both segmental and suprasegmental information and is practically invisible. It thus complements the visual information already available on the face. As we show here, with the voice pitch presented acoustically, normal listeners can lipread a speaker reading continuous text at up to two and a half times the rate possible on the basis of lipreading alone. The pitch signal by itself, of course, is completely unintelligible. Although our work is primarily concerned with methods of electrical stimulation of the cochlea, it has implications for other sensory substitution techniques, the design of special purpose hearing aids and current theories of speech perception.

External electrical stimulation of the cochlea: clinical, psychophysical, speech-perceptual and histological findings.

Our progress towards the development of a particular form of cochlear implant for the totally deaf is described. A single channel stimulation at the round window or promontory is used. This involves a minimum of surgical intervention and infective risk, preserves the possibility of remission and allows the application of later developments. The signal used for stimulation is designed to be matched both to the deaf lip-reader's needs and to his new, restricted, auditory ability. This is done by concentrating on the acoustic pattern components of speech which carry intonation and voiced-voiceless information. Surgical electrophysical, psychoacoustic and speech perceptual aspects of our work with twelve patients are described. The tests involve responses, for example, relating to: threshold for sinusoids; frequency difference limens; periodic -aperiodic discrimination; stress placement; and consonant labelling using combined visual and electrical inputs. Relatively extensive measurements were made with six patients. Significant individual differences were found and the sets of responses provide an essential basis for an appraisal of the potential usefulness of our work to the individual patient. Possible reasons for the individual differences are discussed. A brief indication is given of the techniques which we have developed for the future speech training and speech production evaluation of patients with electro-cochlear voice monitoring. The final section of our paper mentions our histological investigation of the effects of this type of stimulation in the guinea pig.