Effect of Speech Material and Scoring Method on Psychometric Curves for Cochlear Implant Users and Typical Hearing Listeners.

Objectives: Cochlear implants (CIs) are the primary treatment for severe-to-profound hearing loss. For CI users, speech intelligibility (SI) is often excellent in quiet yet degrades dramatically in background noise. Scientific and clinical testing of the effects of noise on SI is routinely performed with speech-in-noise tests. The sensitivity of these tests to signal to noise ratio depends on the slope of their psychometric curve. This slope is not always known for CI users, and direct comparisons between typical hearing (TH) listeners and CI users are lacking.

Design: We present a comparative study of a digit test (DIN), a Matrix sentence test, and an everyday sentence test (LIST) for a group of CI users and TH listeners, with use of word (digit) and sentence (triplet) scoring in the free field. We report descriptive statistics and effect size measures of the psychometric slope and the speech reception threshold (SRT) for each speech test.

Results: For CI users, the slopes of the psychometric curve were significantly shallower and SRTs significantly higher than those of TH listeners. The shallowest slope was seen with the Matrix test. However, the small variances of the slope and the SRT resulted in effect size estimates that fell between those of the other two tests. The DIN test was associated with steeply sloped psychometric curves with low variance. The scoring method did not substantially affect slopes and SRTs for the DIN test and LIST sentences, but word scoring resulted in shallow slopes and substantially worse SRTs for CI users.

Conclusions: The DIN test stood out in this study as an attractive speech-in-noise test for CI users, with steep slopes and low variance in slopes and SRTs among participants. Digit and keyword scoring appear to be viable options for the DIN test and LIST sentences, respectively, potentially increasing the number of available test items. For the Matrix test, sentence scoring yielded shallow slopes and deteriorated SI, especially for the CI group. We recommend word scoring for the Dutch-Flemish Matrix test.