Jay T. Rubinstein

Binaural cochlear implants placed during the same operation

Objective To evaluate the binaural listening advantages for speech in quiet and in noise and to localize sound when independently programmed binaural cochlear implants are used, and to determine whether ears with different hearing ability and duration of profound deafness perform differently with cochlear implants as well as to what extent preimplant psychophysical and physiologic assessment could be predictive of performance. Study Design Prospective study in which patients were prospectively selected to undergo bilateral implantation during a single surgical procedure at a tertiary referral center. All testing was performed with patients using their right, left, or both cochlear implants. Preimplant and intraoperative measures used electrical stimulation at the round window and stimulation through the cochlear implant. Results Bilateral implantation during the same operation did not cause any postoperative problems such as severe vertigo or ataxia. At 1 year, results of speech testing in quiet demonstrated a binaural advantage for 2 of 10 subjects. Speech-in-noise testing demonstrated that two implants were beneficial for two individuals. All subjects benefited from a head shadow effect when an ear with a better signal-to-noise ratio was available. The ability to localize sound was improved with binaural implants in all subjects. Preimplant psychophysical or physiologic measures were not predictive of eventual speech perception performance. Conclusion Binaural cochlear implants can assist in the localization of sounds and have the potential in some individuals to improve speech understanding in quiet and in noise.

How cochlear implants encode speech

Purpose of reviewThis review summarizes the history of cochlear implant signal processing and provides the rationale underlying current approaches. Present strategies are explained and recent research findings are summarized. It is suggested how these results may drive future advancements in signal processing. Recent findingsSubstantial advances have been made in our understanding of the spectral and temporal cues necessary for cochlear implant recipients to perceive music, speech in noise, and interaural timing. It is clear that higher levels of both spectral and temporal resolution, as well as better loudness and pitch coding are necessary for higher levels of performance. These factors are highly interrelated, however, and are beneficial for differing aspects of hearing. Signal processing algorithms incorporating these findings are under active development and some are currently undergoing clinical investigation. SummaryCurrent implant devices, and those soon to be available, have substantial untapped potential to improve the auditory experience of their recipients. It is likely that in the near future, recent findings on pitch and loudness perception, as well as techniques to better emulate the normal functions of the cochlea will result in much higher levels of prosthetic hearing fidelity than are possible today. As the performance of these remarkable devices continues to improve, the population of hearing-impaired individuals who can benefit from implantation is likely to increase significantly.

Spectral-Ripple Resolution Correlates with Speech Reception in Noise in Cochlear Implant Users

Speech perception ability in noise is one of the most practical measures of success with a cochlear implant; however, with experience, this ability can change dramatically over time, making it a less than ideal tool for comparing performance among different processing strategies. This study examined performance on a spectral discrimination task and compared it to speech perception in noise. An adaptive procedure was used to determine the spectral-ripple density that subjects could discriminate. A closed-set, forced-choice adaptive procedure was used to determine speech reception thresholds for words in two-talker babble and in speech-shaped, steady-state noise. Spectral-ripple thresholds (ripples/octave) were significantly correlated with speech reception thresholds (dB SNR) in noise for 29 cochlear implant users (r = −0.55, p = 0.002 in two-talker babble; r = −0.62, p = 0.0004 in steady-state noise), demonstrating that better spectral resolution was associated with better speech perception in noise. A significant correlation was also found between the spectral-ripple discrimination ability and word recognition in quiet (r = 0.50, p = 0.009). In addition, test–retest reliability for spectral-ripple discrimination was good, and no learning was observed. The present study demonstrates that the spectral-ripple discrimination test, which is time efficient and nonlinguistic, would be a useful tool to evaluate cochlear implant performance with different signal processing strategies.

Three-month results with bilateral cochlear implants.

Objectives To evaluate possible binaural listening advantages for speech in quiet, speech in noise, and for localization in a group of postlingually deafened adults with two cochlear implants functioning independently after 3 mo experience. Design Nine postlingually deafened subjects who had received a Cochlear Corporation CI24M implant in each ear were evaluated on a number of tasks. The subjects all had audiometric or biographical (e.g., duration of deafness) differences between the ears. Word and sentence materials were presented to the subjects in quiet and in noise with the signal always in the front and the noise from the front or either side. Results are reported for each ear and for both ears with the noise on either side. This allowed evaluation of head shadow and squelch effects. Additionally, localization ability was assessed for broadband noise presented either to the right or left of center at 45° azimuth. Localization was assessed for each ear and for both ears. Results Results of speech testing in quiet showed a significant advantage for the binaural condition over the better ear in four subjects. In noise, with both signal and noise in front of the subject, a significant advantage of two ears over the better ear was found for four subjects. For noise to one side of the head, when the ear opposite the noise source was added to the ear ipsilateral to the noise, a significant advantage was demonstrated for seven of seven tested subjects. When the ear ipsilateral to the noise was added to the ear contralateral to the noise, a significant advantage was shown for only one of seven (noise on right) and three of seven (noise on left) tested subjects. The localization task showed that all seven tested subjects could discriminate 45° left from 45° right above chance with bilateral stimulation. Three subjects could perform the discrimination above chance with only one ear. However, performance with both ears was significantly better than performance with one ear for two of these latter subjects. Conclusions We conclude that bilateral cochlear implants can provide real advantages, particularly when it is possible to utilize the ear that is away from a noise source, thus taking advantage of the head shadow effect. In addition, localization ability was generally better with two implants than with one.

Electrically evoked single-fiber action potentials from cat: Responses to monopolar, monophasic stimulation

We recorded action potentials from single auditory-nerve fibers of cats using monophasic current pulses delivered by a monopolar intracochlear electrode. These simple stimuli provided a means of investigating basic properties and hypotheses of electrical excitation. Standard micropipette recording techniques were used. Responses to anodic (positive) and cathodic (negative) stimulus pulses were recorded separately to evaluate stimulus polarity effects. Mean spike (action potential) latency was polarity dependent, with greater latencies for cathodic stimulation. Threshold stimulus level was also polarity dependent, with relatively lower cathodic thresholds. Both effects are consistent with trends reported in the compound action potential. Variability in single-fiber latency (i.e., jitter) was dependent upon stimulus polarity. In contrast, the slope of single-fiber input-output functions failed to show a clear polarity dependence, although such trends have been seen in the compound action potential data. We also observed a relatively greater degree of adaptation over time with anodic stimulation. Bimodal post-stimulus-time histograms were recorded in a small number (2%) of fibers, supporting the hypothesis that both the peripheral (dendritic) and central axonal processes are excitable with the same stimulus polarity, in a limited number of cases. This observation, together with analyses of interactions among measures of latency, threshold, and jitter, is consistent with the hypothesis that, with monopolar intracochlear stimulation, most fibers are stimulated at axonal (modiolar) sites and a minority of fibers nearest the electrode are stimulable at their peripheral processes.

Small acoustic neuromas: surgical outcomes versus observation or radiation.

Objective: Evaluate factors affecting outcomes of small acoustic neuroma (AN) removal via a middle cranial fossa (MCF) approach, and compare results to published data on observation and radiation therapy. Study Design: Retrospective chart review. Setting: Academic tertiary referral center. Methods: 162 consecutive patients (ages 19-70) with unilateral AN (0.2-2.5 cm in largest dimension) removed through a MCF approach were reviewed focusing on preservation of hearing, facial nerve function and complications. One hundred thirteen patients had pre-operative word recognition scores (WRS) >70%. Results: Both tumor size and pre-operative WRS were related to post-operative WRS (p < 0.01). Overall, at least some hearing was preserved in 94 (60%) of the 156 patients who had hearing before surgery. If the WRS was also >70% (N = 113), 56 (50%) maintained WRS >70%. Importantly, WRS for 12 others improved to >70% after surgery. When the patients were stratified by tumor size, the patients with small tumors (2-10 mm) faired better than the overall group. At least some hearing was preserved in 65 (72%) of the 90 patients. If the WRS was also >70% (N = 66), 39 (59%) maintained WRS >70%. WRS for eight others improved to >70% after surgery. When the tumor was 1.1-1.4 cm (N = 34), the chance of preserving some hearing decreased to 42% (14/33). If the WRS was also >70% (N = 23), 9 (39%) maintained WRS >70%. WRS for three others improved to >70% after surgery. When the tumor reached 1.5-2.5 cm (N = 35), the hearing preservation rate was 43%. If the WRS was also >70% (N = 24), only eight (33%) maintained WRS of 70%, and one other improved to >70%. The addition of intra-operative whole eighth nerve near field monitoring improved results during small tumor (≤ 1.0 cm) removal preserving some hearing in 80% (32/40) and preserving >70% WRS in 76% (22/29) of those with >70% pre-operative WRS. Good facial nerve function (HB I-II) was achieved in 97% (86% HB I). When tumor size was ≤ 1.0 cm (N = 93), however, good facial nerve function was obtained in 100% (94% HB I). Complications included CSF leak: 9 (5.5%); seizure: 2 (1.2%); and recurrence: 1 (0.6%). Conclusion: Our results suggest that removal of unilateral AN through an MCF approach when the tumor is small and hearing is good provides the best opportunity for hearing preservation and normal facial nerve function. Observation historically results in tumor growth in young and middle-age patients with subsequent hearing loss. Radiation may prevent most tumors from growing, and more data are needed to determine long-term tumor control and hearing preservation rates.

Electrical suppression of tinnitus with high-rate pulse trains.

Hypothesis Application of high-rate pulse trains (e.g., 4800 pps) to the cochlea may represent an effective treatment of tinnitus. Background Tinnitus is a widespread clinical problem with multiple treatments but no cure. A cure for tinnitus would restore the perception of silence. One plausible hypothesis for the origin of tinnitus associated with sensorineural hearing loss is that it is due to loss or alteration of the normal spontaneous activity in the deafferented regions of the cochlea. Electrical stimulation of the cochlea with 5000-pps pulse trains can produce spontaneous-like patterns of spike activity in the auditory nerve. Methods Eleven volunteer human subjects with bothersome tinnitus and high-frequency sensorineural hearing loss underwent myringotomy and temporary placement of a round window electrode. High-rate pulse train stimuli were presented at various stimulus intensities and tinnitus, and stimulus perception were scaled by the subject. Three cochlear implant recipients with tinnitus in the implanted ear underwent similar stimulation. Results Five of 11 (45%) of transtympanic subjects showed substantial or complete tinnitus suppression with either no perception or only a transient perception of the stimulus. Three showed tinnitus suppression only in association with the perception of the stimulus. Three showed no effects on tinnitus. A similar pattern of responses was seen in the cochlear implant subjects. Conclusions Although the study lacked an ideal placebo control, the results are promising and support further research to develop a clinically useful intervention for this troubling disorder.

Comparison of Algorithms for the Simulation of Action Potentials with Stochastic Sodium Channels

AbstractThis paper presents a comparison of computational algorithms to simulate action potentials using stochastic sodium channels. Four algorithms are compared in single-node models: Strassberg and DeFelice (1993) (SD), Rubinstein (1995) (R), Chow and White (1996) (CW), and Fox (1997) (F). Neural responses are simulated to a simple and a preconditioned monophasic current pulse. Three exact algorithms implementing Markov jumping processes (SD, R, CW) resulted in similar responses, while the approximation algorithm using Langevins equation (F) showed quite different responses from those in the exact algorithms. The computational time was measured as well: 1(F), 7(CW), 32(SD), 39(R) relative to that of the F algorithm. Furthermore, it is shown that as the sampling step for integration of the transmembrane potential increases, neural responses in all algorithms tended to be different from those in dense sampling steps, however, the CW algorithm was robust even at a sparse sampling step. It is concluded that the most computationally efficient algorithm having appropriate properties of neural excitability is the CW algorithm.

Current Density Profiles of Surface Mounted and Recessed Electrodes for Neural Prostheses

A Greens function approach has been used to solve Lapalces equation for the quasi-static fields of a recessed, disk electrode. The resulting integral equation was solved numerically using the moment method. An analysis of the error in the approximate solution shows that it must be less than 7 percent for the cases studied. The calculations indicate that a recessed electrode has a more uniform current density profile than a surface mounted electrode. This is true both at the electrode surface, and at the electrode carrier¿tissue junction. The significance of this finding is discussed as is its application to electrochemical, histopathological, and physiological studies of neural prostheses. The clinical use of recessed electrodes in cochlear implants is recommended.

Residual speech perception and cochlear implant performance in postlingually deafened adults.

Objective This study aimed at testing the post-hoc validity of the previously reported predictive index for postoperative cochlear implant performance, based on preoperative duration of deafness, and speech reception. Study Design Adult patients with postlingual severe to profound hearing loss, who were implanted with Cochlear Corporation CI-22 and CI-24 devices were included in this study. We studied the relationship between their postoperative word rec-ognition scores and preoperative factors, namely, duration of deafness, and sentence recognition. We used the same predictive index reported in the previous study to predict their postoperative scores and test the model’s agreement with the actual performance. Results We found that postoperative performance as measured by CNC word scores had an inverse relationship with the duration of deafness, and a direct correlation with the preoperative performance on CID sentence recognition tests. A nonlinear term [Duration / (1+CID)] was shown to improve the correlation coefficient of our predictive index. Conclusion Some predictability of cochlear implant outcome is possible depending on the preoperative duration of deafness and speech recognition abilities. Preoperative residual speech recognition acts as a “trophic factor” that protects the spiral ganglion and/ or the central auditory pathways from degeneration. In other words, it improves the expected postoperative word scores.