Topography of the auditory evoked potential in humans reflects differences between vowels embedded in pseudo-words

To study the processing of vowels embedded in more complex linguistic structures, we compared cortical responses for pseudo-words. Auditory evoked potentials were recorded in 11 right-handed females using a passive oddball paradigm, with /pemu/ and /pomu/ as standard stimuli, differing only with respect to the first syllable. Topographic differences in the N100 were observed between the standards: /pemu/ had larger amplitudes than /pomu/ at more posterior electrode sites whereas a reverse pattern was found at more anterior positions along the midline. This topographic difference can be explained by different generators for the two stimuli. Different vowels and/or the initial formant transition possibly activate different neural populations in the auditory cortex, also when the vowels are embedded in pseudo-words.