An Examination of Sources of Variability Across the Consonant-Nucleus-Consonant Test in Cochlear Implant Listeners

The 10 consonant-nucleus-consonant (CNC) word lists are considered the gold standard in the testing of cochlear implant (CI) users. However, variance in scores across lists could degrade the sensitivity and reliability of them to identify deficits in speech perception. This study examined the relationship between variability in performance among lists and the lexical characteristics of the words. Data are from 28 adult CI users. Each subject was tested on all 10 CNC word lists. Data were analyzed in terms of lexical characteristics, lexical frequency, neighborhood density, bi-, and tri-phonemic probabilities. To determine whether individual performance variability across lists can be reduced, the standard set of 10 phonetically balanced 50-word lists was redistributed into a new set of lists using two sampling strategies: (a) balancing with respect to word lexical frequency or (b) selecting words with equal probability. The mean performance on the CNC lists varied from 53.1% to 62.4% correct. The average difference between the highest and lowest scores within individuals across the lists was 20.9% (from 12% to 28%). Lexical frequency and bi-phonemic probabilities were correlated with word recognition performance. The range of scores was not significantly reduced for all individuals when responses were simulated with 1,000 sets of redistributed lists, using both types of sampling methods. These results indicate that resampling of words does not affect the test–retest reliability and diagnostic value of the CNC word test

A Fast Method for Measuring Psychophysical Thresholds Across the Cochlear Implant Array

A rapid threshold measurement procedure, based on Bekesy tracking, is proposed and evaluated for use with cochlear implants (CIs). Fifteen postlingually deafened adult CI users participated. Absolute thresholds for 200-ms trains of biphasic pulses were measured using the new tracking procedure and were compared with thresholds obtained with a traditional forced-choice adaptive procedure under both monopolar and quadrupolar stimulation. Virtual spectral sweeps across the electrode array were implemented in the tracking procedure via current steering, which divides the current between two adjacent electrodes and varies the proportion of current directed to each electrode. Overall, no systematic differences were found between threshold estimates with the new channel sweep procedure and estimates using the adaptive forced-choice procedure. Test–retest reliability for the thresholds from the sweep procedure was somewhat poorer than for thresholds from the forced-choice procedure. However, the new method was about 4 times faster for the same number of repetitions. Overall the reliability and speed of the new tracking procedure provides it with the potential to estimate thresholds in a clinical setting. Rapid methods for estimating thresholds could be of particular clinical importance in combination with focused stimulation techniques that result in larger threshold variations between electrodes