Use of test-retest measures to evaluate performance stability in adults with cochlear implants

This study was designed to evaluate performance stability with test-retest measures of electrical thresholds, electrical maximum acceptable loudness levels, sound-field thresholds, and audition-only speech tests. The hypothesis was that the standard error of measurement differs from one individual to another for each test, and therefore test-retest measures need to be obtained from each subject.

Test-retest data were obtained in three sets. For the first two sets, data were obtained over 4 successive weeks to determine day-to-day variability. The third set was obtained on 2 successive days, 2 to 10 months later at each subject's annual evaluation. The seven subjects were recipients of the Nucleus cochlear implant and used the Mini Speech Processor at least one year. They were selected because they were available for research testing.

The ranges of electrical thresholds and maximum acceptable loudness levels obtained from each subject during the first two sets were substantially larger on some electrodes than on others. Between set 1 and set 2 for each subject, there were significant differences between thresholds and between maximum acceptable loudness levels on some electrodes. For thresholds as well as maximum acceptable loudness levels, the standard error of measurement across the three sets and 10 electrodes differed among subjects. The group standard error of measurement for sound-field thresholds was small (2 dB). The group standard error of measurement for the NU-6 word test scored according to phonemes (2.75%) was less than half that for the vowel (6.06%) and consonant (5.67%) tests. The standard error of measurement for each speech test differed among subjects.

The standard error of measurement for thresholds as well as maximum acceptable loudness levels varies among electrodes in the same subject and among subjects across electrodes. The standard error of measurement also varies among speech tests for the group as well as among subjects for each speech test. There is little variation in test-retest measures of sound-field thresholds among subjects. These results suggest the clinical importance of obtaining test-retest measures for evaluating the stability of electrical thresholds, electrical maximum acceptable loudness levels, and speech tests.