Effects of noise and spectral resolution on vowel and consonant recognition: acoustic and electric hearing

Current multichannel cochlear implant devices provide high levels of speech performance in quiet. However, performance deteriorates rapidly with increasing levels of background noise. The goal of this study was to investigate whether the noise susceptibility of cochlear implant users is primarily due to the loss of fine spectral information. Recognition of vowels and consonants was measured as a function of signal-to-noise ratio in four normal-hearing listeners in conditions simulating cochlear implants with both CIS and SPEAK-like strategies. Six conditions were evaluated: 3-, 4-, 8-, and 16-band processors (CIS-like), a 6/20 band processor (SPEAK-like), and unprocessed speech. Recognition scores for vowels and consonants decreased as the S/N level worsened in all conditions, as expected. Phoneme recognition threshold (PRT) was defined as the S/N at which the recognition score fell to 50% of its level in quiet. The unprocessed speech had the best PRT, which worsened as the number of bands decreased. Recognition of vowels and consonants was further measured in three Nucleus-22 cochlear implant users using either their normal SPEAK speech processor or a custom processor with a four-channel CIS strategy. The best cochlear implant user showed similar performance with the CIS strategy in quiet and in noise to that of normal-hearing listeners when listening to correspondingly spectrally degraded speech. These findings suggest that the noise susceptibility of cochlear implant users is at least partly due to the loss of spectral resolution. Efforts to improve the effective number of spectral information channels should improve implant performance in noise.     

Effects of amplitude nonlinearity on phoneme recognition by cochlear implant users and normal-hearing listeners

It is widely assumed that the proper transformation of acoustic amplitude to electric amplitude is a critical factor affecting speech recognition in cochlear implant users and normal-hearing listeners. A four-channel noise-band speech processor was implemented, reducing spectral information to four bands. A power-law transformation was applied to the amplitude mapping stage in the speech processor design, and the exponent of the power function varied from a strongly compressive (p = 0.05) to a weakly compressive (p = 0.75) for implant listeners and from 0.3 to 3.0 for acoustic listeners. Results for implants showed that the best performance was achieved with an exponent of about 0.2, and performance gradually deteriorated when either more compressive or less compressive exponents were applied. The loudness growth functions of the four activated electrodes in each subject were measured and those data were well fit by a power function with a mean exponent of 2.72. The results indicated that the best performance was achieved when the normal loudness growth was restored. For acoustic listeners, results were similar to those observed with cochlear implant listeners, except that best performance was achieved with no amplitude nonlinearity (p = 1.0). The similarity of results in both acoustic and electric stimulation indicated that the performance deterioration observed for extreme nonlinearity was due to similar perceptual effects. The function relating amplitude mapping exponent and performance was relatively flat, indicating that phoneme recognition was only mildly affected by amplitude nonlinearity.     

Labeling of musical interval size by cochlear implant patients and normally hearing subjects

OBJECTIVE: To compare the performance of cochlear implant patients and normal-hearing subjects on a musical interval labeling task, and to determine whether information regarding musical interval size is available to cochlear implant patients under realistic everyday listening conditions. DESIGN: Two Nucleus cochlear implant patients listened to musical intervals that consisted of systematic variations of electric pulse rate on single bipolar intracochlear electrode pairs, whereas normal-hearing listeners were presented with the acoustical analog of these stimuli. Subjects labeled the intonation quality of the stimulus intervals ("flat," "sharp," or "in tune"), relative to their memory for specific intervals abstracted from familiar melodies. The cochlear implant patients, in addition, performed this task with realistic acoustical musical stimuli. RESULTS: The interval labeling behavior of cochlear implant subjects, at low pulse rates, was similar to that of normal-hearing subjects. Furthermore, pitch interval information does not appear to be available to cochlear implant subjects when they are listening to acoustical stimuli via their speech processors. CONCLUSIONS: Temporal information appears to be sufficient for the perception of musical pitch. Encoding strategies that are highly successful in restoring speech understanding do not necessarily provide information regarding melodic pitch interval size.     

First field trials with a portable CIS processor for the Ineraid multichannel cochlear implant

The continuous interleaved sampling (CIS) strategy is a promising sound processing strategy for multichannel cochlear implants which provides immediate improvements in speech recognition when tested on Ineraid users: patients with only a few hours of experience (in laboratory testing) with the CIS strategy score better than with the Ineraid prosthesis they used since they, were implanted. The goal of this study was to evaluate the benefits that can be gained by the use of the new strategy in every day life. Two patients, implanted with the Ineraid multichannel cochlear implant, were equipped with a portable numerical processor programmed to implement a high rate CIS strategy. Their speech recognition was evaluated periodically with consonant and vowel identification tests for more than 6 months of use. Tests were also made with the Ineraid processor during the same experimental sessions and patients were regularly interviewed about their experience. Performance with the portable CIS processor was superior or equal to that obtained previously in the laboratory with the same strategy. Both patients achieved the best scores in 6 years of cochlear implant use. Qualitative reports from the patients suggest that the CIS strategy can improve "hearing" performance of cochlear implant users in many important situations of every day life. Altogether, these results hold great promises for all users of the Ineraid multichannel cochlear implant.     

The relation between electric auditory brain stem and cognitive responses and speech perception in cochlear implant users

Electrically evoked brainstem responses (EABR) and event-related cortical potentials were recorded in seven postlingually deaf adults who were experienced users of a Nucleus multichannel cochlear implant. The patients were divided into two subgroups: good performers and moderate performers. Poor EABR were found in two of the moderate performers. The latencies and amplitudes of the cortical N1 P2 complex in the good performers were within the same range as those of subjects with normal hearing, but were deviant in the group of moderate performers. This may indicate disturbed cochleotopical organization of the auditory cortex in the latter group. P300 measurements in the good performers showed normal latencies, whereas in the moderate performers they were prolonged. The results suggest that the outcomes of electrophysiological measurements to assess the integrity of a patient's auditory neural system on a brainstem and a cortical level, are related to the patient's performance with the cochlear implant.     

A new quadruple therapy for the eradication of Helicobacter pylori. Effect of pretreatment with omeprazole on the cure rate

The aim of the study was to assess the speech discrimination ability of postlingually deaf adults implanted with the Combi 40 cochlear implant and to compare the results with the postoperative data published for other devices. The postoperative open and closed set speech perception performance of 21 consecutive patients was tested using a standardized test battery comprising a number, monosyllable, sentence, consonant and vowel discrimination test as well as a rhyme test in the sound only condition. Mean values achieved for each test 1, 6 and 12 months after "switch on" were evaluated. The results demonstrate that all patients have a substantial benefit from their implant and show a continuous improvement in their speech perception abilities with increased device experience. The mean percentages of correct answers after 12 months were 93.4 for numbers, 44.6 for monosyllables, 78.5 for sentences, 67.6 for the rhyme test, 59.8 for vowel, and 67.3 for consonant discrimination. Preoperatively, the mean discrimination score for monosyllables was 0%. The speech discrimination scores of our patients were similar or higher than described for similar patient groups implanted with other devices. The high stimulation rate of the implant system using the continuous interleaved speech processing strategy as well as a deep atraumatic electrode insertion into the apicalmost regions of the scala tympani may be the reason for good performance.     

Improvements in speech perception by children with profound prelingual hearing loss: effects of device, communication mode, and chronological age

The present investigation expanded on an earlier study by Miyamoto, Osberger, Todd, Robbins, Karasek, et al. (1994) who compared the speech perception skills of two groups of children with profound prelingual hearing loss. The first group had received the Nucleus multichannel cochlear implant and was tested longitudinally. The second group, who were not implanted and used conventional hearing aids, was tested at a single point in time. In the present study, speech perception scores were examined over time for both groups of children as a function of communication mode of the child. Separate linear regressions of speech perception scores as a function of age were computed to estimate the rate of improvement in speech perception abilities that might be expected due to maturation for the hearing aid users (n=58) within each communication mode. The resulting regression lines were used to compare the estimated rate of speech perception growth for each hearing aid group to the observed gains in speech perception made by the children with multichannel cochlear implants. A large number of children using cochlear implants (n=74) were tested over a long period of implant use (m=3.5 years) that ranged from zero to 8.5 years. In general, speech perception scores for the children using cochlear implants were higher than those predicted for a group of children with 101-110 dB HL of hearing loss using hearing aids, and they approached the scores predicted for a group of children with 90-100 dB HL of hearing loss using hearing aids.     

Psychophysical and speech perception studies: a case report on a binaural cochlear implant subject

Further improvements in speech perception for cochlear implant patients in quiet and in noise should be possible with speech processing strategies using binaural implants. For this reason, presented here is a series of initial psychophysical and speech perception studies on the authors' first binaural cochlear implant patient. For an approximate matching of the places of stimulation on the two sides, the patient usually reported a single percept when the two sides were simultaneously stimulated. Lateralization was strongly influenced by amplitude differences between the electrical stimuli on the two sides, but only weakly by interaural time delays. Speech testing, comparing monaural with binaural electrical stimulation, showed a binaural advantage particularly in noise.     

Integrin associated proteins

The Clarion cochlear implant was developed in the USA and received FDA approval in August 1996. It consists of an implantable cochlear stimulator (ICS), speech processor with headpiece, and in addition, a clinician's programming system and portable cochlear implant tester. One of the features of the device is its stimulation-coding process for which two methods of continuous interleaved sampling (CIS) and compressed analogue (CA) are applicable. Regardless of which is used, stimulation can be provided over 8 channels. The device was used in 2 cases. Both patients were operated on in October 1996, and 16 electrodes in 8 pairs were mounted in the cochlea. Mapping, performed 3 weeks after the operation, showed good speech perception in both patients with only a cochlear implant in the "open-set" status. CIS was used as the stimulation-coding method. CA has yet to be applied.     

Cognitive and affective functioning in Parkinson''s disease patients with lateralized motor signs

OBJECTIVE: This study aimed to compare recordings of the electrically evoked whole nerve action potential (EAP) made using the reverse telemetry system of the Nucleus CI24M device with those recorded from individuals who use the Ineraid cochlear implant system. STUDY DESIGN: Data were collected in a prospective fashion from Nucleus CI24M cochlear implant users and compared with retrospective data collected from patients who use the Ineraid device. SETTING: All data were collected at the Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics. PATIENTS: Data are reported from 8 patients who use the Nucleus CI24M cochlear implant and 20 patients who use the Ineraid cochlear implant system. INTERVENTIONS: The interventions described in this study were diagnostic in nature. MAIN OUTCOME MEASURES: EAP growth and refractory recovery data are reported. EAP thresholds recorded from patients who use the Nucleus CI24M device also are compared with behavioral thresholds for the stimulus used to evoke the EAP as well as the stimulation levels needed to program the speech processor. RESULTS: EAP morphology, growth, and refractory recovery functions recorded using the Nucleus CI24M reverse telemetry system compared favorably with similar measures recorded from Ineraid cochlear implant users. CONCLUSIONS: Reasonable EAP responses can be recorded using the Nucleus CI24M device. More data are needed to determine whether the information about neural responsiveness available with this device will be clinically useful.     

Effects of contralateral speech competition on auditory event-related potentials recorded from elderly listeners: brain map study

Topographic brain mapping was used to investigate the ability of young and elderly female listeners to attend to tones at one ear in the presence of speech competition at the opposite ear. An oddball stimulus presentation paradigm was used to record the N1, P2, and P300 components of the late auditory evoked potential from 19 scalp locations. With speech competition, elderly listeners exhibited significantly larger reductions in N1 amplitude than did young listeners. This suggests that N1 may provide an electrophysiologic index of age-related breakdowns in processing sounds in the presence of background competition. An unexpected difference was also found between young and elderly listeners in P300 scalp topography. While the young listeners' P300 response was centered at midline for both left and right ear stimulation, the elderly participants had P300 maxima centered in the parietal area of the hemisphere located contralateral to the test ear. This suggests that some of the functional properties (e.g., timing, strength, orientation) of the P300 neural generators may change with age or, alternatively, that different generators may be operative in elderly listeners.     

Cochlear implantation of children with minimal open-set speech recognition skills

OBJECTIVE: The purpose of this study was to evaluate the postoperative performance of 12 children who demonstrated some open-set speech recognition skills before receiving a Nucleus multichannel cochlear implant with a view toward expanding the selection criteria for cochlear implant candidacy to include children who derive minimal benefit from amplification. DESIGN: Pre- and postoperative performance of two groups of children were compared. Group 1 consisted of 12 children who demonstrated some open-set speech recognition skills before receiving a Nucleus multichannel cochlear implant (Borderline group). Group 2 consisted of 12 children who demonstrated no open-set speech recognition skills before implantation with a Nucleus device (Traditional group). In all children, candidacy was determined based on preimplant binaural aided performance. For most subjects, the poorer ear was selected for implantation. Mean pre- and postoperative speech recognition scores of the Borderline subjects were compared to determine the benefit provided by their cochlear implants. Secondly, matched-pair analyses were used to compare the mean speech recognition scores obtained by the Borderline and Traditional subjects. RESULTS: The scores of the Borderline group improved significantly on five of six speech recognition measures when 6 mo postoperative scores obtained with the implant were compared with preoperative test scores obtained with hearing aids. By the 12 mo postoperative interval, the scores of the Borderline group had improved significantly (p < 0.05) on all six measures. In contrast, scores obtained by the Traditional group had improved significantly on three of six measures at both the 6 and 12 mo postoperative intervals. Comparison of postoperative test scores revealed that the Borderline group scored significantly higher than the Traditional group on three of six measures at the 6 mo test interval and on six of six measures at the 12 mo test interval (p < 0.05). CONCLUSIONS: The findings of this study indicate that both groups derive significant benefit from their cochlear implants. Although the mean preoperative audiograms for the implanted ears did not differ significantly for the two groups of subjects, members of the Borderline group exhibited significantly better speech recognition skills than the Traditional group during the first year after implantation. These findings suggest that the increased auditory experience of the Borderline subjects positively influenced their performance with a cochlear implant. The authors advocate that the selection criteria used to determine pediatric cochlear implant candidacy be broadened to include consideration of children who demonstrate minimal open-set speech recognition skills.     

Auditory event related potentials in major depression: prolonged P300 latency and increased P200 amplitude

BACKGROUND: Some studies have shown disturbances in auditory event related potentials (AERPs) in patients with major depression. METHODS: In this exploratory study, the late AERP components, N100 (latency), P200 (amplitude and latency) and P300 (amplitude and latency) were recorded in 68 subjects, i.e. 39 major depressed subjects, with (n=4) or without (n=35) cognitive deterioration, 18 patients with Alzheimer's dementia (SDAT) and 11 normal volunteers. Twenty-five major depressed patients had repeated measurements of AERPs both before and after treatment with antidepressants. RESULTS: Major depressed subjects without cognitive deterioration had significantly higher P300 latency and P200 amplitude than normal volunteers. SDAT patients and major depressed patients with cognitive impairment had a significantly higher P300 latency than depressed patients without cognitive impairment. In the latter, no significant alterations in any of the AERP components upon subchronic treatment with antidepressants were recorded. Nonresponders to antidepressant therapy had significantly higher pretreatment P300 latency and P200 amplitude than responders to treatment (P=0.006) and normal volunteers (P=0.0004). CONCLUSIONS: The findings may suggest that delayed P300 latency as well as increased P200 amplitude accompany major depression and may predict a nonresponse to subsequent antidepressive therapy.     

Dual temporal pitch percepts from acoustic and electric amplitude-modulated pulse trains

Two experiments examined the perception of unmodulated and amplitude-modulated pulse trains by normally hearing listeners and cochlear implantees. Four normally hearing subjects listened to acoustic pulse trains, which were band-pass filtered between 3.9 and 5.3 kHz. Four cochlear implantees, all postlinguistically deaf users of the Mini System 22 implant, listened to current pulse trains produced at a single electrode position. In the first experiment, a set of nine loudness-balanced unmodulated stimuli with rates between 60 and 300 Hz were presented in a multidimensional scaling task. The resultant stimulus spaces for both subject groups showed a single dimension associated with the rate of the stimuli. In the second experiment, a set of ten loudness-balanced modulated stimuli was constructed, with carrier rates between 140 and 300 Hz, and modulation rates between 60 and 150 Hz. The modulation rates were integer submultiples of the carrier rates, and each modulation period consisted of one higher-intensity pulse and one or more identical lower-intensity pulses. The modulation depth of each stimulus was adjusted so that its pitch was judged to be higher or lower 50% of the time than that of an unmodulated pulse train having a rate equal to the geometric mean of the carrier and modulation rates. A multidimensional scaling task with these ten stimuli resulted in two-dimensional stimulus spaces, with dimensions corresponding to carrier and modulation rates. A further investigation with one normally hearing subject showed that the perceptual weighting of the two dimensions varied systematically with modulation depth. It was concluded that, when filtered appropriately, acoustic pulse trains can be used to produce percepts in normal listeners that share common features with those experienced by subjects listening through one channel of a cochlear implant, and that the central auditory system can extract two temporal patterns arising from the same cochlear location.     

Microsurgical C-2 ganglionectomy for chronic intractable occipital pain

The P300 event-related brain potential (ERP) was elicited with visual stimuli using an oddball task in which the subjects made button press responses to discriminate target and standard stimuli. Each stimulus occurred randomly with a 0.50 probability, and 10 trial blocks were presented at 10-min inter-block-intervals (IBIs). P300 amplitude declined reliably across trial blocks, and an interaction between trial block number and electrode site was observed. No habituation effects were found for P300 latency or for N100, P200, or N200 amplitude. The results suggest that P300 amplitude from visual stimuli habituates when short IBIs and a sufficient number of trial blocks are employed. Theoretical implications are discussed with respect to attentional resource allocation and context updating.     

Electrically evoked compound action potential (ECAP) of the cochlear nerve in response to pulsatile electrical stimulation of the cochlea in the rat: effects of stimulation at high rates

Some cochlear implant patients achieve better speech recognition with pulsatile electrical stimulation presented at high rates. The present study aimed to explore, in an animal model of cochlear implants, how the excitability of the cochlear nerve is affected by pulsatile electrical stimulation delivered at high rates, of up to 1,000-2,000 pulses per second (pps). Adult rats (n=23) were implanted with two or three stimulating electrodes in the left cochlea. In four of these rats, the left cochlea was deafened by local perfusion with 1 per cent or 4 per cent neomycin solutions prior to implantation. Pulsatile stimuli consisted of 20 micros electrical pulses, delivered in trains of 200 ms duration, separated by a pause of 200 ms. The pulse rates ranged from 100 to 2,000 pps (intra-train pulse rate). Electrically evoked compound action potentials (ECAPs) of the cochlear nerve were recorded either intracochlearly or from epidural electrodes (extra-cochlearly). With increasing pulse rates, the average ECAP amplitude decreased, whereas the average ECAP latency and its variability (SD) increased. For rates above 300 pps, the amplitude of the ECAP to the individual successive pulses delivered in the train progressively decreased during the initial part of the train, corresponding to a short-term adaptation of the cochlear nerve. This effect progressively increased for pulse rates ranging from 300 to 2,000 pps. In addition, there was a phenomenon of long-term adaptation, as indicated by a decrease in the amplitude of the ECAP to the first pulse of the train, indicating that the pause of 200 ms between each train was not long enough for full recovery of the cochlear nerve. This long-term adaptation was progressively more pronounced for increasing pulse rates. To characterize further the recovery in excitability of the cochlear nerve, forward masking experiments were conducted, showing a decrease of the ECAP amplitude when the interval between the first pulse (masker) and the second pulse (probe) was shorter than 2 ms. This ECAP decrease was slow for intervals between 2 and 1 ms and then abrupt for shorter intervals. The observations described above were similar for extra- and intra-cochlear recordings and were little, if at all, affected by treatment of the cochlea with neomycin.     

Discrimination of temporal asymmetry in cochlear implantees

Several studies have recently demonstrated that normal-hearing listeners are sensitive to short-term temporal asymmetry in the envelopes of sinusoidal or noise carriers. This paper presents a study in which cochlear implantees were presented trains of current pulses with temporally asymmetric envelopes through one channel of an implant that stimulates the auditory nerve directly, thereby bypassing cochlear processes. When the level of the stimuli was adjusted to fit their audibility range, the implantees were able to discriminate temporal asymmetry over a much wider range than normal-hearing listeners. The results suggest that the perception of temporal asymmetry is limited by compression in the normal cochlea.     

Markers from event-related potential subcomponents and reaction time for information processing dysfunction in schizophrenia

Event-related potentials (ERPs) can serve as markers for cognitive processing stages. Identification of those ERPs altered in schizophrenia offer information about cognitive dysfunction. Auditory evoked potentials (AEPs) were elicited within an oddball paradigm in 35 schizophrenic patients and compared with 35 healthy controls. N100 and P200, as well as N200, frontal P300 and parietal P300 subcomponents, were separated using dipole source analysis. The amplitudes of the N100 and the parietal P300 measured in schizophrenics were diminished. The input-related processing stages (N100 and P200) were not altered, whereas later, the deviant and task-related processes (N200, frontal P300, parietal P300 and reaction time) were significantly prolonged in schizophrenia.     

Electrode discrimination and speech recognition in postlingually deafened adult cochlear implant subjects

This study investigated the relationship between electrode discrimination and speech recognition in 11 postlingually deafened adult cochlear implant subjects who were implanted with the Nucleus/Cochlear Corporation multichannel device. The discriminability of each electrode included in a subject's clinical map was measured using adaptive and fixed-level discrimination tasks. Considerable variability in electrode discriminability was observed across subjects. Two subjects could discriminate all electrodes, and discrimination performance by the remaining nine subjects varied from near perfect to very poor. In these nine subjects, the results obtained from the discrimination tasks were used to create a map that contained only discriminable electrodes, and subjects' performance on speech recognition tasks using this experimental map was measured. Four different speech recognition tests were administered: a nine-choice closed-set medial vowel recognition task, a 14-choice closed-set medial consonant recognition task, the NU6 Monosyllabic Words Test [T. W. Tillman and T. Carhart, Tech. Rep. No. SAM-TR-66-55, USAF School of Aerospace Medicine, Brooks Air Force Base, Texas (1966)] scored for both words and phonemes correct, and the Central Institute for the Deaf (CID) Everyday Sentences test [H. Davis and S. R. Silverman, Hearing and Deafness (Holt, Rinehart, and Winston, New York, 1978)]. Seven of the nine subjects tested with the experimental map showed significant improvement on at least one speech recognition measure, even though the experimental map contained fewer electrodes than the original map. Three subjects' scores improved significantly on the CID Everyday Sentences test, three subjects' scores improved significantly on the NU6 Monosyllabic Words test, and five subjects' scores improved significantly on the NU6 Monosyllabic Words test scored for phonemes correct. None of the subjects' scores improved significantly on either the vowel or consonant tests. No significant correlation was observed between electrode discrimination ability and speech recognition scores or between electrode discrimination ability and improvement in speech recognition scores when programmed with the experimental map. The results of this study suggest that electrode discrimination tasks may be used to improve speech recognition of some cochlear implant subjects, and that each electrode site does not necessarily provide perceptually distinct information.     

Intensity discrimination and auditory brainstem responses in cochlear implant and normal-hearing listeners

Intensity-discrimination limens (IDLs) and auditory brainstem responses (ABRs) were measured as a function of stimulus intensity in 6 cochlear implant (CI) and 8 normal-hearing (NH) listeners. Pulse-train stimuli were delivered electrically to the auditory nerve in CI listeners and acoustically in NH listeners. In CI listeners, the IDLs expressed as Weber fractions decreased monotonically with increasing intensity. In NH listeners, a nonmonotonic IDL function showing a peak a midintensities was observed. ABR wave amplitudes increased regularly with intensity only in CI listeners. Results support the notion that the slight decrease in Weber's fractions with increasing sound intensity--generally referred to as "the near-miss to Weber's law"--is subtended by retrocochlear processes, whereas the increase in Weber's fractions at midlevels--known as "the severe departure from Weber's law"--originates in cochlear mechanisms.