Abstract
Musical syntax has been studied mainly in terms of “syntactic irregularity” in harmonic/melodic sequences. However, “perceptual ambiguity” referring to the uncertainty of judgment/classification of presented stimuli can in addition be involved in our musical stimuli using three different chord sequences. The present study addresses how “syntactic irregularity” and “perceptual ambiguity” on musical syntax are dissociated, in terms of effective connectivity between the bilateral inferior frontal gyrus (IFGs) and superior temporal gyrus (STGs) by linearized time-delayed mutual information (LTDMI). Three conditions were of five-chord sequences with endings of dominant to tonic, dominant to submediant, and dominant to supertonic. The dominant to supertonic is most irregular, compared with the regular dominant to tonic. The dominant to submediant of the less irregular condition is the most ambiguous condition. In the LTDMI results, connectivity from the right to the left IFG (IFG-LTDMI) was enhanced for the most irregular condition, whereas that from the right to the left STG (STG-LTDMI) was enhanced for the most ambiguous condition (p = 0.024 in IFG-LTDMI, p < 0.001 in STG-LTDMI, false discovery rate (FDR) corrected). Correct rate was negatively correlated with STG-LTDMI, further reflecting perceptual ambiguity (p = 0.026). We found for the first time that syntactic irregularity and perceptual ambiguity coexist in chord stimulus testing musical syntax and that the two processes are dissociated in interhemispheric connectivities in the IFG and STG, respectively.
Highlights
Right anterior negativity (ERAN) appearing with the negative peak at about 100–200 ms from stimulus onset reflects the degree of expectation violations in chordal and melodic sequences; i.e., the more a chord and a melody are unexpected, and the more the peak amplitude of the Early right anterior negativity (ERAN) increases (Koelsch et al, 2000; Koelsch and Jentschke, 2010)
The linearized time-delayed mutual information (LTDMI) were calculated for 12 connections among four regions of interest (ROIs) of the bilateral inferior frontal gyrus (IFGs) and superior temporal gyrus (STGs) for three conditions of the T, SM, and ST in 19 participants
The processing of syntactic irregularity and perceptual ambiguity in the three conditions was dissociated in the IFG-LTDMI, and the STG-LTDMI, respectively
Summary
Right anterior negativity (ERAN) appearing with the negative peak at about 100–200 ms from stimulus onset reflects the degree of expectation violations in chordal and melodic sequences; i.e., the more a chord and a melody are unexpected, and the more the peak amplitude of the ERAN increases (Koelsch et al, 2000; Koelsch and Jentschke, 2010). Syntactic Irregularity and Perceptual Ambiguity known as the generator of ERAN (Maess et al, 2001). In our previous magnetoencephalography (MEG) study on the ERAN (Kim et al, 2011), using three different stimuli, which consisted of three levels of “regular” (dominant to tonic), “less irregular” (dominant to submediant), and “irregular” (dominant to supertonic) conditions on the conditional probability, the ERAN was not observed in the less irregular condition but in the irregular condition. Our hypothesis is first that the connectivity between the bilateral IFGs would be increased with the “dominant to supertonic,” eliciting the largest ERAN. Perceptual ambiguity refers to the uncertainty of judgment/classification of presented stimuli. The “dominant to submediant” of the less irregular condition might elicit a neural response to perceptual ambiguity in areas other than the IFG, instead of the ERAN. We tested whether the LTDMI reflecting perceptual ambiguity would be correlated with correct rate (CR) in the behavioral experiment, since the more ambiguous it is to distinguish the conditions, and the lower CR will be
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