[Show abstract][Hide abstract] ABSTRACT: Sharp spatial selectivity is critical to auditory performance, particularly in pitch-related tasks. Most contemporary cochlear implants have employed monopolar stimulation that produces broad electric fields, which presumably contribute to poor pitch and pitch-related performance by implant users. Bipolar or tripolar stimulation can generate focused electric fields but requires higher current to reach threshold and, more interestingly, has not produced any apparent improvement in cochlear-implant performance. The present study addressed this dilemma by measuring psychophysical and physiological spatial selectivity with both broad and focused stimulations in the same cohort of subjects. Different current levels were adjusted by systematically measuring loudness growth for each stimulus, each stimulation mode, and in each subject. Both psychophysical and physiological measures showed that, although focused stimulation produced significantly sharper spatial tuning than monopolar stimulation, it could shift the tuning position or even split the tuning tips. The altered tuning with focused stimulation is interpreted as a result of poor electrode-to-neuron interface in the cochlea, and is suggested to be mainly responsible for the lack of consistent improvement in implant performance. A linear model could satisfactorily quantify the psychophysical and physiological data and derive the tuning width. Significant correlation was found between the individual physiological and psychophysical tuning widths, and the correlation was improved by log-linearly transforming the physiological data to predict the psychophysical data. Because the physiological measure took only one-tenth of the time of the psychophysical measure, the present model is of high clinical significance in terms of predicting and improving cochlear-implant performance.
Hearing research 11/2011; 283(1-2):45-58. DOI:10.1016/j.heares.2011.11.005 · 2.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A multichannel cochlear implant (CI) is designed to take advantage of the tonotopic arrangement of auditory nerve fibers within a cochlea. The electrically evoked compound action potential (ECAP) is a safe and reliable objective measure for qualifying neural survival and local spatial resolution in the cochlea. The present study was aimed to explore the effect of recording position on the ECAP Amplitude Growth Function (AGF). The stimulating electrode (EL) was fixed at EL8, in the middle of the electrode array in 6 Clarion II or HiRes 90K subjects. The ECAP AGFs were obtained respectively from two recording positions (EL6 and EL10) using monopolar stimulation mode. The result showed that, in all subjects for both EL6 and EL10 recording positions, the ECAP is a linear function of stimuli level (Mean R2= 0.96, standard deviation =0.06). Moreover, there was a significant correlation of the ECAP AGFs recorded from EL6 and EL10. These results demonstrate the fundamentals of the electrical hearing and will be utilized in the clinical application for diagnosing neural degeneration of CI users.
[Show abstract][Hide abstract] ABSTRACT: This paper discusses virtual channels of cochlear implant, which is produced by simultaneous or sequential activation of adjacent cochlear implant electrodes. Virtual channels create and transfer more available spectral pitch information with the limited number of fixed electrodes, which can be recognized as pitch percepts intermediate to those produced by each electrode separately. This technique not only utilizes the interaction of electrodes but also increases the number of place-pitch steps available to cochlear implant listeners. Virtual channels could be used to realize speech recognition in noisy environment, in enjoying music, and in understanding Chinese language. The study of virtual channels would significantly enhance the traditional cochlear implant therapy and benefit people suffering severe to profound hearing loss.
Sheng wu yi xue gong cheng xue za zhi = Journal of biomedical engineering = Shengwu yixue gongchengxue zazhi 12/2009; 26(6):1384-7.
[Show abstract][Hide abstract] ABSTRACT: This paper discusses the technology of combined electric and acoustic stimulation (EAS) of the auditory system, which is a new therapy for the patients suffering from severe to profound high- and mid-frequency hearing loss but still having their low-frequency hearing. EAS uses hearing aid and cochlear implant technology together in the same ear. The hearing aid acoustically amplifies at low-frequencies, while the cochlear implant electrically stimulates at mid- and high-frequencies. The inner ear processes acoustic and electric stimuli simultaneously. This technique can provide substantial benefit in speech understanding for individuals with severe high-frequency hearing loss and can maintain their residual lower-frequency acoustic hearing. The study of EAS would significantly enhance the conventional cochlear implant therapy and benefit the patients afflicted with severe to profound hearing loss.
Sheng wu yi xue gong cheng xue za zhi = Journal of biomedical engineering = Shengwu yixue gongchengxue zazhi 10/2009; 26(5):1146-9.