Jacobsen, T. (2004). Mismatch negativity to frequency changes: no evidence from human event-related brain potentials for categorical speech processing of complex tones resembling vowel formant structure. Neuroscience Letters, 362(3), 204-208.
Based on a memory-comparison process, changes in the pitch of repetitive sounds are pre-attentively detected, reflected by the mismatch negativity (MMN) event-related brain potential. In the present investigation of categorical speech perception, complex tones were used that consisted of vowel-defining F1 and F2 formant information while not being perceived as speech. MMN was obtained in oddball blocks. The auditory system tracks two simultaneous changes in formant frequencies of 50 Hz while also abstracting from three levels of intensity variation. Lower frequency deviants elicited larger MMN. No effects of language-categorical processing were observed.