Contour Array Research Articles

Cochlear implants in children: safety as well as speech and language

The development of cochlear implants for children at the University of Melbourne and the Bionic Ear Institute, has consisted of a routine of biological and engineering safety followed by evaluation of speech processing strategies on adults before they are undertaken on children. The initial safety studies were to ensure that insertion was atraumatic, the electrical stimulus parameters did not lead to loss of ganglion cells and that the electrode could be inserted without the risk of middle ear infection leading to meningitis. The initial second formant extraction scheme was shown to produce significant open-set speech understanding in adults and was approved by the US Food and Drug Administration (FDA) in 1985. Following this, an international study was undertaken for the FDA on children using a strategy that also included the first formant, and was approved in 1990. Additional advances in speech processing have been evaluated on adults. However, before using one with high rates of stimulation, it was tested for safety on experimental animals. Further advances have been anticipated in particular through the development of a peri-modiolar array, the Nucleus Contour. Prior to its use on adults, it was tested in the human temporal bone and found to lead to minimal trauma. It was evaluated in adults and found to lead to better current localization and lower thresholds. A study was undertaken in children using a spectral maxima scheme at high rates (advanced combination encoder (ACE)) and the Contour array as it had given best results in adults. It was approved as safe and effective for use in children in 2000. Studies were also undertaken to look at plasticity and visual dominance particularly through cognitive studies and the use of the McGurk effect. This demonstrated that deaf children with implants rely heavily on visual information and there is a great need to have unambiguous auditory stimuli to get best results.

Cochlear implants in Children: safety as well as speech and language

The development of cochlear implants for children at the University of Melbourne/Bionic Ear Institute has consisted of a routine of biological and engineering safety followed by evaluation of speech processing strategies on adults before they are undertaken on children. The initial safety studies were to ensure that insertion was atraumatic, the electrical stimulus parameters did not lead to loss of ganglion cells and that the electrode could be inserted without the risk of middle ear infection leading to meningitis.The initial second formant extraction scheme was shown to produce significant open set speech understanding in adults and was approved by the U.S. Food and Drug Administration (FDA) in 1985. Following this, an international study was undertaken for the FDA on children using a strategy that also included the first formant, and was approved in 1990.Additional advances in speech processing have been evaluated on adults. However, before using one with high rates os stimulation it was tested for safety on experimental animals. Further advances have been anticipated in particular through the development of a perimodiolar array, the Nucleus “Contour.” Prior to its use on adults, it was tested in the human temporal bone and found to lead to minimal trauma. It was evaluated in adults and found to lead to better current localization and lower thresholds. A study was undertaken in children using a spectral maxima scheme at high rates (ACE) and the contour array as it had given best results in adults. It was approved as safe and effective for use in children in 2000.Studies have also been undertaken to look at plasticity and visual dominance particularly through cognitive studies and the use of the McGurk effect. This demonstrated that deaf children with implants rely heavily on visual information and there is a great need to have unambiguous auditory stimuli to get best results.

Threshold, comfortable level and impedance changes as a function of electrode-modiolar distance.

The study investigated the hypothesis that threshold and comfortable levels recorded from cochlear implant patients would reduce, and dynamic range increase, as distance of the electrode from the modiolar wall (radial distance) decreases. Two groups of cochlear implant patients participated; one group using the Nucleus' 24 Contour electrode array, and one group using the Nucleus standard straight (banded) array. The Nucleus 24 Contour array has been shown in temporal bone studies to lie closer to the modiolus than the banded array. The relationship of electrode impedance and radial distance is also investigated. The study, conducted at three centers, evaluated 21 patients using the Contour array, and 36 patients using the banded array. For each patient, threshold, comfortable levels and dynamic range were measured at four time points. Common ground electrode impedance was recorded clinically from each patient, at time intervals up to 12 wk. An estimate of the radial distance of the electrode from the modiolus was made by analysis of Cochlear view x-rays. Threshold and comfortable levels were significantly lower for the Nucleus 24 Contour array than for the banded array. However, dynamic range measurements did not show the predicted increase. In a majority of subjects, a significant correlation was found between the estimated radial distance of the electrode from the modiolus and the measured threshold and comfortable levels. This trend was not observed for dynamic range. The analysis indicates that other factors than radial distance are involved in the resultant psychophysical levels. Clinical impedance measures (common ground) were found to be significantly higher for the Contour array. However, the electrodes on the Contour array are half-rings, which are approximately only half the geometric size of the full rings as electrodes of the standard array. When the geometric electrode area in the two array designs are normalized, the trends in the electrode impedance behavior are similar. The results support the hypothesis that the relationship between the radial distance of the electrode and the psychophysical measures are influenced by patterns of fibrous tissue growth and individual patient differences, such as etiology and neural survival. Impedance measures for the Nucleus 24 Contour electrode array were higher than the banded electrode array, but this is primarily due to the reduction in electrode surface area. The different outcomes in impedance over time suggest differences in the relative contributions of the components of impedance with the two arrays.

The nucleus 24 contour cochlear implant system: adult clinical trial results.

The purpose of this article is to present psychophysical data for 40 Nucleus 24 Contour adult patients with 1 mo of device experience and speech perception results for a group of 56 adult patients with 3 mo experience using the Nucleus 24 Contour cochlear implant system. Postoperative hearing thresholds (i.e., under headphones) in the implanted ear were also assessed in a group of 85 patients who had measurable hearing preoperatively. This was of interest because preservation of residual hearing, postoperatively, is consistent with atraumatic insertion of the electrode array. In addition, data will be presented that reflected feedback from 40 surgeons who participated in the trial. Participants in this study were 18 yr of age or older, with bilateral severe to profound sensorineural hearing loss with no congenital component. Preoperatively, they scored < or = 50% open-set sentence recognition (HINT sentences) in the ear to be implanted and < or = 60% in the best-aided condition. The investigation was a repeated-measures single-subject experiment and took place at 46 different North American clinical sites. Preoperative performance was compared with postoperative performance 3 mo after device activation. Clinicians were able to program patients' processors with one, two, or all three speech-processing strategies. Testing took place using the participant's preferred speech-processing strategy (SPEAK, CIS, or ACE). Preoperative unaided hearing thresholds were compared with unaided thresholds in the implanted ear measured 1 mo after device activation. Surgeons were canvassed regarding surgical use and design of the device via a questionnaire after having completed at least one Nucleus 24 Contour surgery. Average T- and C-levels for the Nucleus 24 Contour patients were considerably lower than those using the Nucleus 24 (CI24M). A total of 85 patients had measurable hearing preoperatively at two or more audiometric frequencies in the ear implanted. Of these patients 41 (48%) had measurable hearing at one or more frequencies and 32 (38%) had measurable hearing at two or more frequencies postoperatively. In general, surgeons found the Nucleus 24 Contour easy to insert and were pleased with the design features of the device. The downsized receiver/stimulator (of the Nucleus 24 Contour) required less drilling than the Nucleus 24, reducing surgical time, as well as making the Contour better suited for implantation in those with small skull sizes (e.g., small children and infants). After 3 mo of device use, mean open-set speech perception in quiet and in noise was significantly better than preoperative performance on all test measures. Patients using the ACE strategy had significantly better mean scores for all measures than patients using SPEAK. Only two patients preferred to use the CIS coding strategy. CONCLUSIONS The results presented in this article demonstrated that the design objectives of the Nucleus 24 Contour were met. Namely, results from this study, together with insertion studies, were consistent with perimodiolar placement using an implant design that the majority of surgeons found easy to insert with relatively minimal trauma. Reduced T- and C-levels were observed with Contour patients when compared with patients using the Nucleus 24 with the straight array, consistent with perimodiolar placement. A survey of surgeons participating in the clinical trial indicated easier, or equally easy, insertion of the Contour array, compared with previous Nucleus products as well as other manufacturers' devices, without the use of additional insertion tools or array positioners. Postoperatively, 46% of patients with preoperative residual hearing maintained some level of unaided hearing postoperatively, suggesting atraumatic insertion of the Nucleus 24 Contour electrode array. It is worth noting that all 216 patients implanted during this study had full insertions of their Contour electrode arrays. High levels of open-set speech perception in quiet and in noise were achieved and patients using the ACE strategy had significantly better mean scores for all measures than patients using SPEAK. Only two patients preferred to use the CIS coding strategy.

The contour electrode array: safety study and initial patient trials of a new perimodiolar design.

The aim of these studies was to investigate the insertion properties and safety of a new intracochlear perimodiolar electrode array design (Contour). An electrode array positioned close to the neural elements could be expected to reduce stimulation thresholds and might potentially reduce channel interaction. Two sequential studies were conducted. In study 1, the Contour electrode array was inserted in 12 human temporal bones. After cochlear surface preparation, the position of the array was noted and the basilar membrane was examined for insertion damage. On the basis of the outcome of this temporal bone study, study 2 investigated the Contour array, mounted on a Nucleus CI-24 M device and implanted in three adult patients. Study I showed that in 10 temporal bones, the Contour array was positioned close to the modiolus, and the basilar membrane was intact. In the two remaining bones, the arrays had pierced the basilar membrane and were positioned in the scala vestibuli apical to the penetration. Statistical analysis showed an equivalent probability of insertion-induced damage of the two array designs. In study 2, image analysis indicated that the Contour electrodes were positioned closer to the modiolus than the standard Nucleus straight array. Lower T and C levels, but higher impedance values, were recorded from electrodes close to the modiolus. Initial speech perception data showed that all patients gained useful open-set speech perception, two patients achieving scores of 100% on sentence material 3 months postoperatively. The temporal bone studies showed the Contour electrode array to be generally positioned closer to the modiolus than the standard Nucleus straight array, and to have an equivalent probability of causing insertion-induced damage.

Brain damage and global stereopsis.

When a single object lies in front of or beyond the plane of fixation its retinal image lies on disparate positions in the two eyes. This 'local' retinal disparity is an excellent cue to depth, and retinal disparties of a few seconds of arc are detectable by people and monkeys. However, most visual scenes produce a complex array of contours in each eye and we can detect the disparity in the arrays despite the ambiguous nature of the disparities, i.e. each contour in one eye could be related to any of several similar contours in the other eye. This ability, known as 'global' stereopsis, may be selectively impaired following brain damage in man. Global stereopsis was measured in rhesus monkeys before and after removing a different cortical visual area in different groups of animals. Only removal of the inferotemporal cortex impaired global stereopsis. The result is related to the findings with human patients and to receptive field properties of neurons in the inferotemporal cortex of monkeys.

Computer processing of SEM images by contour analyses

Techniques involving the computer processing of scanning electron microscope (SEM) images using a contour approach have been developed. For each picture from one to six different SEM signals are converted from analog to digital form and recorded on magnetic tape for subsequent computer analysis. A program finds and analyzes coordinate arrays representing the reconstructed computer picture. Least squares fitting of the contour arrays to ellipses provides measurements of the aspect ratios and orientations of the picture fields. Line integration techniques produce areas and perimeters. Computer plotting enables both the visual comparison of the reconstructed picture with a photograph of the image on the cathode ray tube of the SEM and an estimate of the accuracy of the ellipse fits.