Syllable Inference as a Mechanism for Spoken Language Understanding

A classic problem in spoken language comprehension is how listeners perceive speech as being composed of discrete words, given the variable time-course of information in continuous signals. We propose a syllable inference account of spoken word recognition and segmentation, according to which alternative hierarchical models of syllables, words, and phonemes are dynamically posited, which are expected to maximally predict incoming sensory input. Generative models are combined with current estimates of context speech rate drawn from neural oscillatory dynamics, which are sensitive to amplitude rises. Over time, models which result in local minima in error between predicted and recently experienced signals give rise to perceptions of hearing words. Three experiments using the visual world eye-tracking paradigm with a picture-selection task tested hypotheses motivated by this framework. Materials were sentences that were acoustically ambiguous in numbers of syllables, words, and phonemes they contained (cf. English plural constructions, such as "saw (a) raccoon(s) swimming," which have two loci of grammatical information). Time-compressing, or expanding, speech materials permitted determination of how temporal information at, or in the context of, each locus affected looks to, and selection of, pictures with a singular or plural referent (e.g., one or more than one raccoon). Supporting our account, listeners probabilistically interpreted identical chunks of speech as consistent with a singular or plural referent to a degree that was based on the chunk's gradient rate in relation to its context. We interpret these results as evidence that arriving temporal information, judged in relation to language model predictions generated from context speech rate evaluated on a continuous scale, informs inferences about syllables, thereby giving rise to perceptual experiences of understanding spoken language as words separated in time.