Michael Ziese

Comparison of the TEMPO+ ear-level speech processor and the cis pro+ body-worn processor in adult MED-EL cochlear implant users.

A study was conducted to compare the new MED-EL TEMPO+ ear-level speech processor with the CIS PRO+ body-worn processor in the COMBI 40/COMBI 40+ implant system. Speech tests were performed in 46 experienced subjects in two test sessions approximately 4 weeks apart. Subjects were switched over from the CIS PRO+ to the TEMPO+ in the first session and used only the TEMPO+ in the time between the two sessions. Speech tests included monosyllabic word tests and sentence tests via the telephone. An adaptive noise method was used to adjust each subject’s scores to approximately 50%. Additionally, subjects had to complete a questionnaire based on their 4 weeks of experience with the TEMPO+. The speech test results showed a statistically significant improvement in the monosyllabic word scores with the TEMPO+. In addition, in the second session, subjects showed a significant improvement when using the telephone with the TEMPO+, indicating some learning in this task. In the questionnaire, the vast majority of subjects found that the TEMPO+ allows equal or better speech understanding and rated the sound quality of the TEMPO+ higher. All these objective and subjective results indicate the superiority of the TEMPO+ and are mainly attributed to a new coding strategy called CIS+ and its implementation in the TEMPO+. In other words, based on the results of this study, it appears that after switching over from the CIS PRO+ to the TEMPO+, subjects are able to maintain or even improve their own speech understanding capability.

Speech Understanding with the CIS and the n-of-m Strategy in the MED-EL COMBI 40+ System

Speech tests have been performed on 6 subjects for comparing the standard 12-channel continuous interleaved sampling (CIS) strategy (CIS12), the 7-channel CIS strategy (CIS7) and the 7-of-12 strategy in the MED-EL COMBI 40+ system. An ABAB experimental design was used whereby each strategy was reversed and replicated. Speech tests were performed in quiet (vowels, consonants, monosyllables, sentences) and noise (sentences). Results showed that for vowels, CIS12 is significantly superior to CIS7, for consonants and sentences CIS12, CIS7 and 7-of-12 performed equally well, and that for monosyllables 7-of-12 is significantly superior to both CIS12 and CIS7. In addition, 7-of-12 is superior to CIS7 by almost the same amount as CIS12, but in this case the difference is not significant. Further, all strategies have been found to be equally robust in noise with respect to sentence understanding. The differences between CIS12 and 7-of-12 on the one hand and CIS7 on the other hand may be attributed to decreased spectral resolution of the latter. The fact that – in contrast to what has been reported for the SPEAK strategy – 7-of-12 is equally robust in noise as the CIS strategies is explained by the use of higher stimulation rates, wider frequency bands and a higher percentage of channels stimulated in each cycle.

Analysis of ceiling effects occurring with speech recognition tests in adult cochlear-implanted patients.

This article presents a simple method of analysing speech test scores which are biased through ceiling effects. Eighty postlingually deafened adults implanted with a MED-EL COMBI 40/40+ cochlear implant (CI) were administered a numbers test and a sentence test at initial device activation and at 1, 3, 6, 12 and 24 months thereafter. As a measure for speech recognition performance, the number of patients who scored at the ‘ceiling level’ (i.e. at least 95% correct answers) was counted at each test interval. Results showed a quick increase in this number soon after device activation as well as a continuous improvement over time (numbers test: 1 month: 51%; 6 months: 73%; 24 months: 88%; sentence test: 1 month: 33%; 6 months: 49%; 24 months: 64%). The new method allows for the detection of speech recognition progress in CI patient samples even at late test intervals, where improvement curves based on averaged scores are usually assuming a flat shape.

Development of a Speaker Discrimination Test for Cochlear Implant Users Based on the Oldenburg Logatome Corpus

The purpose of the study was to develop a speaker discrimination test for cochlear implant (CI) users. The speech material was drawn from the Oldenburg Logatome (OLLO) corpus, which contains 150 different logatomes read by 40 German and 10 French native speakers. The prototype test battery included 120 logatome pairs spoken by 5 male and 5 female speakers with balanced representations of the conditions ‘same speaker’ and ‘different speaker’. Ten adult normal-hearing listeners and 12 adult postlingually deafened CI users were included in a study to evaluate the suitability of the test. The mean speaker discrimination score for the CI users was 67.3% correct and for the normal-hearing listeners 92.2% correct. A significant influence of voice gender and fundamental frequency difference on the speaker discrimination score was found in CI users as well as in normal-hearing listeners. Since the test results of the CI users were significantly above chance level and no ceiling effect was observed, we conclude that subsets of the OLLO corpus are very well suited to speaker discrimination experiments in CI users.

Time course of auditory streaming: do CI users differ from normal-hearing listeners?

In a complex acoustical environment, the auditory system decides which stimulus components originate from the same source by forming auditory streams, where temporally non-overlapping stimulus portions are considered to originate from one source if their stimulus characteristics are similar. The mechanisms underlying streaming are commonly studied by alternating sequences of A and B signals which are often tones with different frequencies. For similar frequencies, they are grouped into one stream. Otherwise, they are considered to belong to different streams. The present study investigates streaming in cochlear implant (CI) users, where hearing is restored by electrical stimulation of the auditory nerve. CI users listened to 30-s long sequences of alternating A and B harmonic complexes at four different fundamental frequency separations, ranging from 2 to 14 semitones. They had to indicate as promptly as possible after sequence onset, if they perceived one stream or two streams and, in addition, any changes of the percept throughout the rest of the sequence. The conventional view is that the initial percept is always that of a single stream which may after some time change to a percept of two streams. This general build-up hypothesis has recently been challenged on the basis of a new analysis of data of normal-hearing listeners. Using the same experimental paradigm and analysis, the present study found that the results of CI users agree with those of the normal-hearing listeners: (i) the probability of the first decision to be a one-stream percept decreased and that of a two-stream percept increased as Δf increased, and (ii) a build-up was only found for 6 semitones. Only the time elapsed before the listeners made their first decision of the percept was prolonged as compared to normal-hearing listeners. The similarity in the data of the CI user and the normal-hearing listeners indicates that the quality of stream formation is similar in these groups of listeners.

Logatome discrimination in cochlear implant users: subjective tests compared to the mismatch negativity.

This paper describes a logatome discrimination test for the assessment of speech perception in cochlear implant users (CI users), based on a multilingual speech database, the Oldenburg Logatome Corpus, which was originally recorded for the comparison of human and automated speech recognition. The logatome discrimination task is based on the presentation of 100 logatome pairs (i.e., nonsense syllables) with balanced representations of alternating “vowel-replacement” and “consonant-replacement” paradigms in order to assess phoneme confusions. Thirteen adult normal hearing listeners and eight adult CI users, including both good and poor performers, were included in the study and completed the test after their speech intelligibility abilities were evaluated with an established sentence test in noise. Furthermore, the discrimination abilities were measured electrophysiologically by recording the mismatch negativity (MMN) as a component of auditory event-related potentials. The results show a clear MMN response only for normal hearing listeners and CI users with good performance, correlating with their logatome discrimination abilities. Higher discrimination scores for vowel-replacement paradigms than for the consonant-replacement paradigms were found. We conclude that the logatome discrimination test is well suited to monitor the speech perception skills of CI users. Due to the large number of available spoken logatome items, the Oldenburg Logatome Corpus appears to provide a useful and powerful basis for further development of speech perception tests for CI users.

Visualization of stimulation patterns in cochlear implants: Application to event-related potentials (P300) in cochlear implant users

Auditory P300 potentials obtained in cochlear implant users were evoked with tone bursts designed to reflect the frequency stimulation patterns of intracochlear electrodes. To visualize these stimulation patterns in MED-EL COMBI 40+ cochlear implants, we calculated color-coded plots of the charge of each stimulus pulse as a function of time and stimulation channel (stimulograms). The aim of this study was to investigate the effect of stimulation patterns on event-related potentials, such as the P300. The influence of electrode separation on the P300 response in postlingually deaf adults using a cochlear implant is demonstrated in two examples.

Melody and chord discrimination of cochlear implant users in different pitch ranges

Abstract Objective The study assesses the ability of cochlear implant (CI) recipients to discriminate music excerpts, namely melodies and chords. Natural instrument recordings were used to test whether an improved fine-structure transmission is beneficial for this task at low pitches. Methods Seventeen CI recipients using either a continuously interleaved strategy (CIS) strategy or fine-structure coding (FSP) had to discriminate melody pairs played by the violin or the cello, and pairs of chords differing at high or low pitches. The examples were taken from the Mu.S.I.C. perception test. Results In the melody task, no differences were found according to pitch range or processing strategy. In the chords task, changes in the low-pitch range provided a significantly greater difficulty for CI recipients using the CIS stategy and correct detection was reduced by 11.1% compared to the detection of high-pitch changes. This drop in performance was reduced in the FSP users to 7.4% correct and was statistically not significant. Conclusions When musical chords played with natural instrument are discriminated by CI users, a fine-structure coding strategy provides some benefit at low pitches. No benefit was found in the discrimination of unaccompanied melodies.

Diskrimination musikalischer Tonhöhen bei Patienten mit Kochleaimplantat

BACKGROUND Numerous people with cochlear implants (CI) report difficulties in listening to music even though they understand speech quite well. One reason for this is a limited perception of pitch and timbre. In this study ability of adult CI subjects to discriminate musical pitch is investigated. PATIENTS AND METHODS In two psychoacoustic experiments, each conducted in 10 adult CI subjects provided with MED-EL Combi 40+ cochlear implant devices and a control group of subjects with normal hearing, individual discrimination abilities for musical pitch perception were determined. To investigate the influence of the group of instruments on discrimination ability, stimuli representing four different groups of instruments were used: woodwind (clarinet), brass (trumpet), strings (violin) and keyboard instruments (piano). RESULTS The discrimination thresholds determined varied between individual CI subjects, and on average they were significantly higher for the piano than for the other three instruments. CONCLUSIONS The results show that in subjects with CI pitch perception differs from instrument to instrument and is in general worse than in persons with normal hearing.

Überlegungen zur bilateralen CI-Versorgung

Patienten mit einer beidseitigen, an Taubheit grenzenden innenohrbedingten Hörstörung werden seit nunmehr 20 Jahren erfolgreich mit Kochleaimplantat (CI)-Systemen therapiert. Dabei erschien es aus rehabilitativen und finanziellen Gründen bisher ausreichend, die Prothese einseitig zu implantieren. Nun tritt auch die bilaterale CI-Versorgung in den Blickpunkt des Interesses. Als mögliche Vorteile einer bilateralen CI-Versorgung sind Verbesserungen der Schalllokalisation und des Sprachverständnisses im Störlärm zu erwarten. Obwohl bisher nur sehr wenige wissenschaftlich fundierte human- und tierexperimentelle Ergebnisse über den Nutzen der beidseitigen CI-Versorgung vorliegen [10], wurden Patienten beidseitig implantiert. Vor- und Nachteile der bilateralen CI-Versorgung werden seitdem sehr kontrovers diskutiert. Im Mittelpunkt der Diskussion stehen vorwiegend gesundheitspolitische Überlegungen und technische Aspekte, wohingegen dem Problem der zentralnervösen Verarbeitung wenig Aufmerksamkeit gewidmet wird.Ziel dieses Artikels ist es, die möglichen neurobiologischen und technischen Vor- und Nachteile einer bilateralen CI-Versorgung gleichermaßen zu beleuchten.