Simultaneous Tracking of Coevolving Distributional Regularities in Speech

Speech processing depends upon mapping variable acoustic speech input in a manner that reflects the long-term regularities of the native language. Yet, these mappings are flexible such that introduction of short-term distributional regularities in speech input, like those arising from foreign accents or talker idiosyncrasies, leads to rapid adjustments in the effectiveness of acoustic dimensions in signaling phonetic categories. The present experiments investigate whether the system is able to track simultaneous short-term distributional statistics present in speech input or if, instead, the global regularity jointly defined by these distributions dominates. Three experiments establish that adult listeners are able to track distinct simultaneously evolving regularities across time, given information to support the "binning" of acoustic instances. Both voice quality and visual information to indicate talker supported tracking of coevolving distributional regularities, even when the regularities are opposing and even when the acoustic speech tokens contributing to the distinct distributions are identical. This indicates that reweighting of perceptual dimensions in response to short-term regularities in speech input is not simply an accumulation of acoustic instances. Rather, the system is able to track multiple context-sensitive regularities simultaneously, with rapid context-dependent adaptive adjustments in how acoustic speech input maps to phonetic categories. Public Significance Statement We often encounter talkers whose speech departs from the norm due to a foreign accent or speech idiosyncrasy. Research demonstrates that listeners rapidly adapt to unusual or unexpected patterns of speech. But what is involved in this adaptation? The present experiments reveal that the perceptual system quickly adjusts the effectiveness of specific features of the speech input (like voice pitch) in signaling speech sounds like /b/ or /p/ that differentiate beer from pier. These adjustments are initiated when the detailed correlations among acoustic properties of speech shift in the input. Surprisingly, the system is not fooled when speech input blends competing correlations. Instead, listeners use information about voice and talker to simultaneously track coevolving correlations in speech input.