Auditory-evoked magnetic field codes place of articulation in timing and topography around 100 milliseconds post syllable onset.

This study demonstrates by means of magnetic source imaging how consonants and vowels that constitute a syllable differently affect the neural processing within the auditory cortex. We recently identified a topographically separate processing for mutually exclusive place features in isolated vowels (Obleser et al., in press). Does this mapping principle also hold for stop consonants with differing places of articulation? How is the N100m response to consonant-vowel (CV) syllables affected by the congruency of place information in the consonant and the vowel? Moreover, how is the N100m affected by coarticulation, i.e., the spreading of place features to adjacent phonemes? By systematically varying phonological information in the consonant as well as in the vowel of CV syllables, we were able to reveal a difference in N100m syllable source location along the anterior-posterior axis due to mutually exclusive places of articulation in the vowel of the syllable. We also found a change in source orientation rather than source location due to the same mutually exclusive features in the onset of the syllable. Furthermore, the N100m time course of the brain response delivered important complementary information to identify the phonological features present in the speech signal. Responses to all syllable categories originated in the perisylvian region anterior to the source of a band-passed noise stimulus. The systematic variation of both consonantal and vocalic place features and the study of their interaction on auditory processing proves to be a valuable method to gain more insight into the elusive phenomenon of human speech recognition.