Spike-timing and mean-rate coding of the temporal fine structure and envelope cues in real words

A number of studies over the past decade have argued for the importance of temporal fine structure (TFS) cues for the perception of consonants. However, recent investigations indicate that TFS cues from consonants may largely be converted into envelope (ENV) cues by narrowband cochlear filtering, such that these cues are conveyed by the mean-rate response of auditory nerve fibers rather than spike-timing cues. However, these studies used nonsense VCV syllables, and this result may not generalize to real words in which the patterns of ENV and TFS cues may be substantially different, and in which lexical context may play a role. In this study, we used a computational model of the auditory periphery and neural-based speech intelligibility predictors to investigate the TFS and ENV representation of real words from the NU-6 database. Spike-timing and mean-rate cues were evaluated for “auditory chimaeras” created from this database, in which the TFS of one signal is mixed with the ENV of another. The results indicate that the chimaera processing has a bigger impact in general on the mean-rate representation of phonemes than on the spike-timing representation, and inclusion of the spike-timing cues gives better predictions of phoneme perception. [Funded by NSERC of Canada.]