Brain imaging correlates of temporal quantization in spoken language

Psychophysical research has established that temporalintegration windows of several different sizes are critical for the analysis of any acoustic speech signal. Recent work from our laboratory has examined speech processing in the human auditory cortex using both hemodynamic (fMRI, PET) and electromagnetic (MEG, EEG) recording techniques. These studies provide evidence for at least two distinct temporal scales relevant to the integration and processing of speech at the cortical level - a relatively short window of 25-50 ms and a longer window of 150- 300 ms. In addition to support for processing on these time scales, there is also evidence for hemispheric asymmetry in temporal quantization. Left auditory cortex shows enhanced sensitivity to rapid temporal changes (possibly associated with segmental and subsegmental perceptual analysis), while right auditory cortex is more sensitive to slower changes (possibly associated with syllabic rate processing and dynamics of pitch).