Multiple routes to the perceptual learning of speech.

A listener's ability to utilize indexical information in the speech signal can enhance their performance on a variety of speech perception tasks. It is unclear, however, whether such information plays a similar role for spectrally reduced speech signals, such as those experienced by individuals with cochlear implants. The present study compared the effects of training on linguistic and indexical tasks when adapting to cochlear implant simulations. Listening to sentences processed with an eight-channel sinewave vocoder, three separate groups of subjects were trained on a transcription task (transcription), a talker identification task (talker ID), or a gender identification task (gender ID). Pre- to posttest comparisons demonstrated that training produced significant improvement for all groups. Moreover, subjects from the talker ID and transcription training groups performed similarly at posttest and generalization, and significantly better than the subjects from the gender ID training group. These results suggest that training on an indexical task that requires high levels of controlled attention can provide equivalent benefits to training on a linguistic task. When listeners selectively focus their attention on the extralinguistic information in the speech signal, they still extract linguistic information, the degree to which they do so, however, appears to be task dependent.