A key feature of speech is the quasi-regular rhythmic information contained in its slow amplitude modulations. In this article we review the information conveyed by speech rhythm, and the role of ongoing brain oscillations in listeners’ processing of this content. Our starting point is the fact that speech is inherently temporal, and that rhythmic information conveyed by the amplitude envelope contains important markers for place and manner of articulation, segmental information, and speech rate. Behavioral studies demonstrate that amplitude envelope information is relied upon by listeners and plays a key role in speech intelligibility. Extending behavioral findings, data from neuroimaging—particularly electroencephalography (EEG) and magnetoencephalography (MEG)—point to phase locking by ongoing cortical oscillations to low-frequency information (~4–8 Hz) in the speech envelope. This phase modulation effectively encodes a prediction of when important events (such as stressed syllables) are likely to occur, and acts to increase sensitivity to these relevant acoustic cues. We suggest a framework through which such neural entrainment to speech rhythm can explain effects of speech rate on word and on segment perception (i.e., that the perception of phonemes and words in connected speech are influenced by preceding speech rate). Neuroanatomically, acoustic amplitude modulations are processed largely bilaterally in auditory cortex, with intelligible speech resulting in additional recruitment of left hemisphere regions. Notable among these is lateral anterior temporal cortex, which we propose functions in a domain-general fashion to support ongoing memory and integration of meaningful input. Together, the reviewed evidence suggests that low frequency oscillations in the acoustic speech signal form the foundation of a rhythmic hierarchy supporting spoken language, mirrored by phase-locked oscillations in the human brain.

/pdf/neural-oscillations-carry-speech-rhythm-through-to-2z11pieook.pdf

Neural Oscillations Carry Speech Rhythm through to Comprehension.

On the just noticeable difference for tempo in speech

http://www.homepages.ucl.ac.uk/~uclyyix/yispapers/Xu_JPhon2010_author_version.pdf

In defense of lab speech

Rate effects on Swedish VOT : Evidence for phonological overspecification

The rate of context speech can influence phonetic perception. This study investigated the bounds of rate dependence by observing the influence of nonspeech precursor rate on speech categorization. Three experiments tested the effects of pure-tone precursor presentation rate on the perception of a [ba]-[wa] series defined by duration-varying formant transitions that shared critical temporal and spectral characteristics with the tones. Results showed small but consistent shifts in the stop-continuant boundary distinguishing [ba] and [wa] syllables as a function of the rate of precursor tones, across various manipulations in the amplitude of the tones. The effect of the tone precursors extended to the entire graded structure of the [w] category, as estimated by category goodness judgments. These results suggest a role for durational contrast in rate-dependent speech categorization.

/pdf/perceptual-effects-of-preceding-nonspeech-rate-on-temporal-1vfnd5ud8k.pdf

Perceptual effects of preceding nonspeech rate on temporal properties of speech categories.

Many studies have shown that listeners process speech in a rate-dependent manner, altering the location of phonetic category boundaries in accord with the acoustic consequences of a change in rate during speech production. In a recent series of papers that focused on a voicing contrast, we reported that the perceptual adjustment for rate is not limited to the region of the category boundary, but extends to well within the category, producing a change in which stimuli are perceived to be the best category exemplars. In the current paper, we provide evidence for the generality of this effect by showing analogous results for a /b/-/w/ contrast, specified by transition duration. The implications of these findings for models of rate-dependent processing are discussed.

Timothy B. O’Rourke

Papers

Internal structure of phonetic categories: effects of speaking rate.