Evidence for rapid auditory perception as the foundation of speech processing:: a sparse temporal sampling fMRI study

We examined the processing of verbal and nonverbal auditory stimuli using an event-related functional magnetic resonance imaging (fMRI) study to reveal the neural underpinnings of rapid temporal information processing and it's relevance during speech perception. In the context of a clustered sparse-temporal fMRI data collection eight right-handed native German speakers performed: (i) an auditory gap detection task; and (ii) a CV syllable discrimination task. A tone perception task served as a nontemporal control condition. Here we aimed to research to what extent the left hemisphere preferentially processes linguistically relevant temporal information available in speech and nonspeech stimuli. Furthermore, we sought to find out as to whether a left hemisphere's preference for linguistically relevant temporal information is specifically constrained to verbal utterances or if nonlinguistic temporal information may also activate these areas. We collected haemodynamic responses from three time points of acquisition (TPA) with varying temporal distance from stimulus onset to gain an insight on the time course of auditory processing. Results show exclusively left-sided activations of primary and secondary auditory cortex associated with the perception of rapid temporal information. Furthermore, the data shows an overlap of activations evoked by nonspeech sounds and speech stimuli within primary and secondary auditory cortex of the left hemisphere. The present data clearly support the assumption of a shared neural network for rapid temporal information processing within the auditory domain for both speech and nonspeech signals situated in left superior temporal areas.