Learning Effects in Psychophysical Tests of Spectral and Temporal Resolution

Psychophysical tests of spectral and temporal resolution, such as the spectral-ripple discrimination task and the temporal modulation detection test, are valuable tools for the evaluation of cochlear implant performance. Both tests correlate with speech intelligibility and are reported to show no instantaneous learning effect. However, some of our previous trials have suggested that there is a learning effect over time. The aim of this study was to investigate the test-retest reliability of the two tests when measured over time.

Ten adult cochlear implant recipients, experienced with the HiResolution speech coding strategy, participated in this study. Spectral ripple discrimination and temporal modulation detection ability with the HiResolution strategy were assessed both before and after participation in a previous trial that evaluated two research speech coding strategies after 2 weeks of home-usage. Each test was repeated six times on each test day.

No improvement was observed for same-day testing. However, comparison of the mean spectral ripple discrimination scores before and after participation in the take-home trial showed improvement from 3.4 to 4.8 ripples per octave (p < 0.001). The mean temporal modulation detection thresholds improved from -15.2 to -17.4 dB (p = 0.035).

There was a clear learning effect over time in the spectral and temporal resolution tasks, but not during same-day testing. Learning effects may stem from perceptual learning, task learning, or a combination of those two factors. These results highlight the importance of a proper research design for evaluation of novel speech coding strategies, where the baseline measurement is repeated at the end of the trial to avoid false-positive results as a consequence of learning effects.