What in the temporal structure of speech triggers speech-specific processing

The precise role of cortical oscillations in speech processing is under investigation. According to current research, the phase alignment of Δ/θ-band (2-8 Hz) neural oscillations in the auditory cortex is involved in the segmentation of speech. Neural oscillations in the θ band correspond to the slow energy fluctuations in the speech signal at the syllabic rate.

Recently, Overath, McDermott, Zarate and Poeppel [2015] showed that brain regions involved in speech-specific processing (i.e. superior temporal sulcus) are activated even by strongly corrupted speech stimuli. Certain structural features of the speech stimuli such as the slow energy fluctuations in the θ band, however, remained intact. Others features such as the fine structure of the signal, as well as pauses and acoustic features that are important for the perception of intonation, were manipulated. A clear delineation of processing speech-specific and non-specific stimuli was observed interms of anatomical localization.

Here we use magnetoencephalographic measurements (MEG) to investigate putative speech-specific neuronal mechanisms. We test first, whether the activation of the speech-specific areas is related to the segmentation of the speech signal in the θ-band. Second, we manipulate the phonological similarities between a native and a foreign language (German vs. Russian) in order to test which stimulus features drive the activation.