Source Location and Orientation, Dipole Moment, and Latency of Magnetic Mismatch Fields May Mirror the Perceptual Salience of Phonetic Contrasts

Abstract

Evoked magnetic field measurements have provided evidence for topographic differences between vowels and consonants with regard to the Nlm component of the magnetically evoked response [1]. However, it has not yet been shown, whether the magnetic mismatch field (MMF) is sensitive to the distinction between vowels and consonants. The mismatch response reflects the detection of a difference between current stimulus input and a trace in sensory memory [2]. Mismatch responses are elicited by rare deviant stimuli presented in the context of frequent standard stimuli. For the electric counterpart of the MMF, the mismatch negativity, it has been shown that the amplitude of the mismatch response is correlated with the discriminability of the eliciting stimulus contrast [3],[4]. It is relatively easy to discriminate perceptually among vowels even when they are presented in noise [5]. Under comparable conditions of ambient noise, it may be difficult to discriminate among plosive stop consonants differing in place of articulation [6]. Thus, it is to be expected that MMF sources activated by vowel and consonant contrasts, respectively, differ in dipole moment amplitude.