Effect of training rate on recognition of spectrally shifted speech

Previous studies have shown that the protocol used for auditory training may significantly affect the outcome of training. However, it is unclear how often training should be performed to maximize its benefit. The present study investigated how the frequency of training contributed to normal-hearing listeners' adaptation to spectrally shifted speech.

Eighteen normal-hearing listeners were trained with spectrally shifted and compressed speech via an 8-channel acoustic simulation of cochlear implant speech processing. Five short training sessions (1 hr per session) were completed by each subject; subjects were trained at one of three training rates: five sessions per week, three sessions per week, or one session per week. Subjects were trained to identify medial vowels presented in a cVc format; depending on the level of difficulty, the number of response choices was increased and/or the acoustic differences between vowels were reduced. Vowel and consonant recognition was measured before and after training as well as at regular intervals during the training period. Sentence recognition was measured before and after training only.

Results showed that pretraining vowel recognition scores were poor (14.0% correct, on average) for all subjects, due to the severe spectral shift. After five sessions of targeted vowel contrast training, there was a significant improvement of shifted vowel recognition for most subjects. The mean improvement was comparable (approximately 15 percentage points) across the three training rate conditions, despite significant intersubject variability in pre- and pretraining baseline performance. There was no significant difference in training outcomes among the three training rates. Spectrally shifted consonant and sentence recognition also improved by approximately 20 percentage points after training, even though consonants and sentences were not explicitly trained. Similar to vowel recognition, there was no significant difference in training outcomes among the three training rates for shifted consonant and sentence recognition.

The results demonstrated that the training rate had little effect on normal-hearing listeners' adaptation to spectrally shifted speech, at least for the training periods (ranging from 1 to 5 wk) used in the present study. The outcome of auditory training may depend more strongly on the amount of training (i.e., total number of training sessions) rather than the frequency of training (i.e., daily or once per week). Although more frequent training may accelerate listeners' adaptation to spectrally shifted speech, there may be significant benefits from training as little as one session per week. The results of the present study suggest that appropriate training schedules can be developed to optimize the effectiveness, efficiency, and effort associated with hearing-impaired patients' auditory rehabilitation.