Abstract
Evaluating series of complex sounds like those in speech and music requires sequential comparisons to extract task-relevant relations between subsequent sounds. With the present functional magnetic resonance imaging (fMRI) study, we investigated whether sequential comparison of a specific acoustic feature within pairs of tones leads to a change in lateralized processing in the auditory cortex (AC) of humans. For this we used the active categorization of the direction (up vs. down) of slow frequency modulated (FM) tones. Several studies suggest that this task is mainly processed in the right AC. These studies, however, tested only the categorization of the FM direction of each individual tone. In the present study we ask the question whether the right lateralized processing changes when, in addition, the FM direction is compared within pairs of successive tones. For this we use an experimental approach involving contralateral noise presentation in order to explore the contributions made by the left and right AC in the completion of the auditory task. This method has already been applied to confirm the right-lateralized processing of the FM direction of individual tones. In the present study, the subjects were required to perform, in addition, a sequential comparison of the FM direction in pairs of tones. The results suggest a division of labor between the two hemispheres such that the FM direction of each individual tone is mainly processed in the right AC whereas the sequential comparison of this feature between tones in a pair is probably performed in the left AC.
Highlights
The perception of complex auditory stimuli like speech and music requires the processing of single sounds and of sequences of auditory stimuli
With the present functional magnetic resonance imaging study, we investigated whether sequential comparison of a specific acoustic feature within pairs of tones leads to a change in lateralized processing in the auditory cortex (AC) of humans
The results suggest a division of labor between the two hemispheres such that the frequency modulated (FM) direction of each individual tone is mainly processed in the right AC whereas the sequential comparison of this feature between tones in a pair is probably performed in the left AC
Summary
The perception of complex auditory stimuli like speech and music requires the processing of single sounds and of sequences of auditory stimuli. The processing of an auditory sequence requires maintaining specific acoustic parameters in memory but in addition, a continuous update of the information in memory in order to process the ongoing parts of the sequence. Such sequential comparisons, are fundamental for language and music processing which require extracting relative changes in a number of different acoustic parameters (e.g., duration, frequency, intensity). Regarding the parameter duration, identifying whether a tone is short or long always requires the comparison with at least one other stimulus For this comparison, it is necessary to hold the information regarding the properties of one stimulus in memory until it can be compared with another stimulus. Parietal, and temporal areas (e.g., auditory cortex, AC) with different lateralization have been shown to be involved in auditory pitch or verbal working memory (Zatorre et al, 1992, 1994; Gaab et al, 2003, 2006; Brechmann et al, 2007; Koelsch et al, 2009; Schulze et al, 2011; Schulze and Koelsch, 2012)
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