Can envelope recovery account for speech recognition based on temporal fine structure?

Abstract

Over the past decade, several studies have demonstrated that normal-hearing listeners can achieve high levels of speech recognition when presented with only the temporal fine structure (TFS) of speech stimuli. Initial suggestions to explain these findings were that they were the result of the auditory system’s ability to recover envelope information from the TFS (envelope recovery; ER). A number of studies have since showed decreasing ER with increasing numbers of analysis filters (the filters used to decompose the signal) while intelligibility from speech-TFS remains almost unaffected. Accordingly, it is now assumed that speech information is present in the TFS. A recent psychophysical study, however, showed that envelope information remains in the TFS after decomposition, suggesting a possible role of ER in speech-TFS understanding. The present study investigated this potential role. In contrast to previous work, a clear influence of analysis filter bandwidth on speech-TFS understanding was established. In addition, it was shown that near perfect speech recognition from recovered envelopes can be achieved with as many as 15 analysis filters. Finally, the relationship between analysis and auditory filter bandwidths was explored in ER. Taken together, the present findings suggest that a role of ER in speech-TFS understanding cannot be excluded.