Selective amplification of stimulus differences during categorical processing of speech

Neuron. 2007 Nov 21;56(4):726-40. doi: 10.1016/j.neuron.2007.11.001.


The brain's perceptual stimuli are constantly changing: some of these changes are treated as invariances and are suppressed, whereas others are selectively amplified, giving emphasis to the distinctions that matter most. The starkest form of such amplification is categorical perception. In speech, for example, a continuum of phonetic stimuli gets carved into perceptually distinct categories. We used fMRI to measure the degree to which this process of selective amplification takes place. The most categorically processing area was the left supramarginal gyrus: stimuli from different phonetic categories, when presented together in a contrasting pair, were neurally amplified more than two-fold. Low-level auditory cortical areas, however, showed comparatively little amplification of changes that crossed category boundaries. Selective amplification serves to emphasize key stimulus differences, thereby shaping perceptual categories. The approach presented here provides a quantitative way to measure the degree to which such processing is taking place.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acoustic Stimulation
  • Adult
  • Auditory Cortex / anatomy & histology
  • Auditory Cortex / physiology
  • Auditory Pathways / anatomy & histology
  • Auditory Pathways / physiology
  • Brain / anatomy & histology
  • Brain / physiology
  • Brain Mapping
  • Cerebrovascular Circulation / physiology
  • Dominance, Cerebral / physiology
  • Evoked Potentials / physiology
  • Female
  • Humans
  • Language Tests
  • Language*
  • Magnetic Resonance Imaging
  • Male
  • Nerve Net / anatomy & histology
  • Nerve Net / physiology
  • Parietal Lobe / anatomy & histology
  • Parietal Lobe / physiology*
  • Phonetics*
  • Psychometrics
  • Speech Perception / physiology*
  • Verbal Behavior / physiology*