High Levels Of Speech Recognition Research Articles

New outcomes with auditory brainstem implants in NF2 patients.

To determine factors related to high levels of speech recognition in patients with the auditory brainstem implant (ABI). Retrospective case review. International multicenter data from hospitals and tertiary referral facilities. Patients with neurofibromatosis type 2 (NF2) and bilateral vestibular schwannomas. ABIs were placed after the removal of vestibular schwannomas. Demographic and surgical data were collected from 26 patients with ABIs who achieved scores of better than 30% correct identification of sentences presented in quiet listening conditions and without lipreading cues. Scores better than 30% speech recognition of standard sentence test materials (HINT or equivalent) in quiet listening conditions were obtained in 26 of the 84 NF2 patients (31%). ABI speech recognition was correlated with surgical position, length of deafness, the number of distinct pitch electrodes, perceptual levels, and ABI stimulation rate, but not correlated with tumor size, tumor stage, the number of electrodes used, or electrophysiological recordings. This paper presents the consensus opinion from a meeting of surgeons to compare outcomes across ABI surgical centers. The consensus opinion was that brainstem trauma is a primary factor in the variability of outcomes in NF2 patients. The significant co-factors in outcomes implied that ABI surgery should be accomplished with great care to minimize physical and venous trauma to the brainstem. It is clear that high levels of speech recognition, including high levels of open-set speech recognition, are possible with the ABI even in patients with NF2 and large tumors.

Can envelope recovery account for speech recognition based on temporal fine structure?

Over the past decade, several studies have demonstrated that normal-hearing listeners can achieve high levels of speech recognition when presented with only the temporal fine structure (TFS) of speech stimuli. Initial suggestions to explain these findings were that they were the result of the auditory system’s ability to recover envelope information from the TFS (envelope recovery; ER). A number of studies have since showed decreasing ER with increasing numbers of analysis filters (the filters used to decompose the signal) while intelligibility from speech-TFS remains almost unaffected. Accordingly, it is now assumed that speech information is present in the TFS. A recent psychophysical study, however, showed that envelope information remains in the TFS after decomposition, suggesting a possible role of ER in speech-TFS understanding. The present study investigated this potential role. In contrast to previous work, a clear influence of analysis filter bandwidth on speech-TFS understanding was established. In addition, it was shown that near perfect speech recognition from recovered envelopes can be achieved with as many as 15 analysis filters. Finally, the relationship between analysis and auditory filter bandwidths was explored in ER. Taken together, the present findings suggest that a role of ER in speech-TFS understanding cannot be excluded.

Editorial

Figure: William F. House, DDS, MDFigure: Mr. WilsonFigure: Dr. BrackmannFigure: Dr. ZengIt is with great sadness that we note the death of William F. House, DDS, MD. Dr. House died at his home in Aurora, OR, on Dec. 7, 2012, six days after he turned 89. “Dr. Bill” is widely known and admired as the father of neurotology for his key role in the development of safe and effective treatments for hearing and balance disorders. He was the first to use a microscope in neurosurgery, and he developed the middle fossa approach and then the translabyrinthine approach for the removal of acoustic neuromas. As a result, the mortality rate for acoustic neuroma operations dropped from 40 percent to less than 1 percent, where it now stands. Prior to Dr. Bill's innovations, preservation of hearing or facial nerve function was not even a goal in acoustic neuroma treatment. Now, virtually all patients have facial nerve function preserved, and many maintain their hearing as well. Dr. Bill's crowning achievement is the development of the first practical cochlear implant (CI). Three large steps led to the development and success of present-day CIs: (1) the pioneering step to implant the first patients with a safe and reliable device that had a life span of many years, (2) the development of devices that provided multiple sites of stimulation in the cochlea to take advantage of the tonotopic organization of the auditory system, and (3) the development of processing strategies that utilized the multiple sites and supported high levels of speech recognition for most users of cochlear implants. More than anyone else, Dr. Bill was responsible for that critical first step. At the outset, many experts opposed cochlear implants, arguing that any useful restoration of hearing with electrical stimulation was a fool's dream. As a result, implantation in humans, particularly children, was considered unethical, as the surgical risks could not be outweighed by any conceivable benefit from the CI. The criticism was vociferous, but Dr. Bill persevered, determined to help deaf people. “The thing that kept me going was that patients could hear, and they told me how much they appreciated it,” he said on Oct. 18, 2012, during his last published interview. (See HJ 2012;65[12]:32 or http://bit.ly/DrBillArticle for the print article, and http://bit.ly/DrBillVideo for the video.) “We implanted a number of children who were 2 or 3 years of age, and one of them even became a linguist.” Without Dr. Bill's determination and pioneering contributions, the development of the cochlear implant would have been greatly delayed, if started at all. We as a field and the hundreds of thousands of deaf and severely hearing-impaired people who have benefitted from CIs owe him the greatest debt of gratitude. His work should serve as a constant reminder: We all stand on the shoulders of giants. CORRECTION In the January issue, in the article “Task Force Finding Underscores Knowledge Gap about Benefits of Hearing Screening,” the title for Jaynee A. Handelsman, PhD, was incorrect. She is director of pediatric audiology at the University of Michigan C.S. Mott Children's Hospital.

Stream segregation on a single electrode as a function of pulse rate in cochlear implant listeners

While cochlear implants (CIs) usually provide high levels of speech recognition in quiet, speech recognition in noise remains challenging. To overcome these difficulties, it is important to understand how implanted listeners separate a target signal from interferers. Stream segregation has been studied extensively in both normal and electric hearing, as a function of place of stimulation. However, the effects of pulse rate, independent of place, on the perceptual grouping of sequential sounds in electric hearing have not yet been investigated. A rhythm detection task was used to measure stream segregation. The results of this study suggest that while CI listeners can segregate streams based on differences in pulse rate alone, the amount of stream segregation observed decreases as the base pulse rate increases. Further investigation of the perceptual dimensions encoded by the pulse rate and the effect of sequential presentation of different stimulation rates on perception could be beneficial for the future development of speech processing strategies for CIs.

Auditory brainstem implants for neurofibromatosis type 2

Neurofibromatosis type 2 (NF2) produces benign Schwann cell tumors on many cranial nerves, in particular on the vestibular portions of the VIIIn bilaterally. Removal of these vestibular schwannomas usually severs the auditory portion of the VIIIn, thus deafening the patients. The auditory brainstem implant (ABI) was designed to provide prosthetic electric stimulation of the cochlear nucleus in the brainstem to restore some hearing sensations to patients deafened by bilateral removal of vestibular schwannomas. This study will review the new developments and improving outcomes of the ABI. From its initial application in 1979 until about 2005, the ABI provided modest but useful auditory sensations to NF2 patients. However, application of the ABI in non-NF2 populations and in children with congenital malformations demonstrated better results, showing that the ABI could provide high levels of speech recognition. Recent results show excellent speech recognition in NF2 patients as well. This study will discuss the potential causes of the variability in ABI outcomes. ABIs activate neurons in the cochlear nucleus to recreate hearing sensations in people who have become deaf as a result of the loss of the auditory nerve. Most NF2 patients show functional hearing benefit from the ABI, with awareness and recognition of environmental sounds and enhancement of lipreading. It is now clear that ABIs can produce excellent speech recognition in some patients with NF2, allowing even conversational telephone use. Although the factors leading to this improved performance are not completely clear, these new results show that excellent hearing is possible for NF2 patients with the ABI.

Auditory recovery and speechreading in cochlear implanted deaf patients: A review

In this review, we discuss evidence from our recent studies and the literature that deaf patients after cochlear implantation partly rely on visual cues during auditory recovery and develop mechanisms of audio-visual integration as a strategy to maintain high levels of speech recognition in the noisy auditory environments provided by cochlear implants. This evidence is considered both at the behavioural level and at the level of cortical activity as explored by studies in functional neuroimaging. Since coupling different modalities facilitates perceptual learning in a single modality, we believe that a strong visually and audio-visually based rehabilitation during the first months after cochlear implantation would significantly improve and hasten the functional recovery of speech intelligibility and other auditory functions in these patients.

Otimização da percepção da fala em deficientes auditivos usuários do sistema de implante coclear multicanal

OBJETIVO: realizar um estudo intra-sujeito, avaliando o reconhecimento da fala e a preferência subjetiva em deficientes auditivos usuários do sistema de implante coclear (IC) Nucleus 24, nas diferentes estratégias de codificação disponíveis nesse sistema (Spectral Peak - SPEAK, Continuous Interleaved Sampler - CIS e Advanced Combination Encoders - ACE), a fim de promover a otimização da percepção da fala em cada sujeito. FORMA DE ESTUDO: Clínico prospectivo. MATERIAL E MÉTODO: Sete adultos com deficiência auditiva pós-lingual foram divididos aleatoriamente em 2 grupos, determinados A e B para a realização do protocolo de avaliação. CIS foi adaptada inicialmente aos sujeitos do grupo A e ACE aos do grupo B. SPEAK foi a linha de base para todos os sujeitos. Foram realizadas avaliações do reconhecimento da fala no silêncio e no ruído (S/R + 10dB), ajustes nas estratégias de codificação e aplicação de questionários de auto-avaliação. RESULTADOS: Altos níveis de reconhecimento da fala foram obtidos para as três estratégias. Os resultados médios dos sete sujeitos atingidos para o reconhecimento de sentenças no silêncio foram de 69,1%, 76,2% e 80,2% para CIS, SPEAK e ACE respectivamente. Na situação de ruído foram de 38,0%, 40,8% e 53,1% para SPEAK, CIS e ACE, respectivamente. Não houve diferença estatisticamente significante entre as estratégias avaliadas. Escores de reconhecimento da fala mais altos foram notados sujeito a sujeito, com a estratégia otimizada. CONCLUSÃO: A utilização de estratégias múltiplas de codificação da fala e escolhas de parâmetros flexíveis permitem ao clínico individualizar um programa de adaptação e resulta em maiores benefícios aos usuários de IC.

Factors that allow a high level of speech understanding by patients fit with cochlear implants.

Three factors account for the high level of speech understanding in quiet enjoyed by many patients fit with cochlear implants. First, some information about speech exists in the time/amplitude envelope of speech. This information is sufficient to narrow the number of word candidates for a given signal. Second, if information from the envelope of speech is available to listeners, then only minimal information from the frequency domain is necessary for high levels of speech recognition in quiet. Third, perceiving strategies for speech are inherently flexible in terms of the mapping between signal frequencies (i.e., the locations of the formants) and phonetic identity.

The perception of phonologically significant contrasts using speech envelope cues.

The observation that many cochlear implantees demonstrate high levels of speech recognition, despite limited or distorted spectral information, has motivated research on the importance of temporal information for the perception of speech. The purpose of this study was to measure the recognition of speech contrasts via only the speech envelope before and after training. Test stimuli consisted of eight segmental and two suprasegmental contrasts of the Hebrew Speech Pattern Contrast test using a binary forced-choice paradigm. Multiplying the speech waveform with white noise eliminated spectral information. Results show that stress, intonation and manner of articulation were very well perceived using only temporal information, whereas voicing and place of articulation were perceived above chance levels. Results also show that vowels were more susceptible to the removal of spectral information than consonants. These findings help to better understand speech perception performance of hearing-impaired individuals, including cochlear implant users. They may also have practical implications for aural rehabilitation and sensory aids design for the Hebrew speaking population.

Speech intelligibility as a function of the number of channels of stimulation for signal processors using sine-wave and noise-band outputs.

Vowels, consonants, and sentences were processed through software emulations of cochlear-implant signal processors with 2-9 output channels. The signals were then presented, as either the sum of sine waves at the center of the channels or as the sum of noise bands the width of the channels, to normal-hearing listeners for identification. The results indicate, as previous investigations have suggested, that high levels of speech understanding can be obtained using signal processors with a small number of channels. The number of channels needed for high levels of performance varied with the nature of the test material. For the most difficult material--vowels produced by men, women, and girls--no statistically significant differences in performance were observed when the number of channels was increased beyond 8. For the least difficult material--sentences--no statistically significant differences in performance were observed when the number of channels was increased beyond 5. The nature of the output signal, noise bands or sine waves, made only a small difference in performance. The mechanism mediating the high levels of speech recognition achieved with only few channels of stimulation may be the same one that mediates the recognition of signals produced by speakers with a high fundamental frequency, i.e., the levels of adjacent channels are used to determine the frequency of the input signal. The results of an experiment in which frequency information was altered but temporal information was not altered indicates that vowel recognition is based on information in the frequency domain even when the number of channels of stimulation is small.

Geneva experience with the Ineraid multichannel cochlear implant.

Ineraid is a multichannel intracochlear implant of recent design that can provide high levels of speech recognition to totally deaf patients. We chose this device when it became available in 1985 because of our clinical and research interests. We had no commercial ties and could therefore critically assess the value of this implant in an array of patients, including congenital deafness, ossified cochleas and perilingual children.

Better speech recognition with cochlear implants

HIGH levels of speech recognition have been achieved with a new sound processing strategy for multielectrode cochlear implants. A cochlear implant system consists of one or more implanted electrodes for direct electrical activation of the auditory nerve, an external speech processor that transforms a microphone input into stimuli for each electrode, and a transcutaneous (rf-link) or percutaneous (direct) connection between the processor and the electrodes. We report here the comparison of the new strategy and a standard clinical processor. The standard compressed analogue (CA) processor presented analogue waveforms simultaneously to all electrodes, whereas the new continuous interleaved sampling (CIS) strategy presented brief pulses to each electrode in a nonoverlapping sequence. Seven experienced implant users, selected for their excellent performance with the CA processor, participated as subjects. The new strategy produced large improvements in the scores of speech reception tests for all subjects. These results have important implications for the treatment of deafness and for minimal representations of speech at the auditory periphery.