Fig 1.
(A) Notation of the four stimuli used in the experiment.
(B) Power spectral density plots (Welch's method) illustrate the formation of each chord by moving the middle tone in the 3-tone chords progressively further from C#5 (major triad). Harmonic overtones are illustrated up to 3 kHz. The frequency differences between the first and second tones of the dissonant chord (27 Hz), and their first harmonics (54 Hz), are indicated for the dissonant chord above the plot. (C) For each chord, the amplitude envelope of the signal in a narrow frequency band centered on the base tone (440 Hz) is plotted above the corresponding energy spectrogram (measured in dB, dark areas represent relatively higher energy than light areas). The dissonant chord is characterized by strong amplitude envelope modulation at a rate of 27 Hz, corresponding to a 37 ms period.
Fig 2.
Time-frequency representations of MEG responses to musical chords reveal prominent stimulus-locking and amplitude modulation of oscillations in a wide frequency range (TFRs averaged over all subjects, chords, and over MEG planar gradiometers).
A) Left Panel. TFR shows significant PL relative to the baseline period averaged over all subjects and all MEG-sensors (Wilcoxon's signed rank test, p < .01; FDR corrected). Robust PL between 3 and 75 Hz is observed both during early (0–100 ms) and late (100–400 ms) post-stimulus periods. Shaded areas represent TF-elements for which less than 2% of channels exhibited a significant effect. Right panel. The sensor topographies of selected TF-ROIs are illustrated in the sensor layouts. PL is strongest in the temporal channels. Shaded areas represent channels for which less than 2% of T-elements exhibited a significant effect. B) Left Panel. TFR shows significant AM relative to baseline averaged as in A (Student's t test, p < .01; FDR corrected). Positive AM is observed in a broad frequency range during the first few hundred ms. The positive AM is followed by negative AM in the alpha (8–12 Hz) and beta / gamma (18–40 Hz) frequency bands. Right panel. The positive AM is most pronounced in the bilateral temporal channels whereas the late negative AM in the 10 − 40 Hz range is observed in a slightly left-lateralized fronto-parietal and temporal network. Inset; Outline of the Elekta Neuromag Vectorview sensor helmet when flattened to 2D and seen from above (L = left, R = right, F = front, B = back).
Fig 3.
Main effect of musical expertise (Group) on response amplitude (2-way ANOVA, p < .01; FDR corrected) induced by musical chords.
A group difference in AM was observed 5 to 10 Hz range from 0 to 300 ms post-stimulus, and localized to bilateral temporal sensors (insert). Only those TF-elements (channels) that survive the test of p < .01 (FDR-corrected) in at least 2% of channels (TF-elements) are shown (see Methods for details).
Fig 4.
Main effect of musical expertise (Group) and Group by Chord interaction on PL (2-way ANOVA, p < .01; FDR-corrected) induced by musical chords.
A) A main effect of Group (musicians > non-musicians, red-yellow color scale) was observed in a wide frequency range between 3 and 60 Hz, and a Group by Chord interaction (black-green color scale) in the gamma band. Only those TF-elements that survived the test of p < .01 (FDR-corrected) in at least 2% of channels are shown. B) The sensor topographies for the selected TF-ROIs show the spatial distribution of the main effect of Group, where only those channels that survived the test of p < .01 (FDR-corrected) in at least 2% of TF-elements are shown. Musicians exhibited stronger PL in a widespread network, with pronounced effects in temporal, parietal and central sensors. C) The sensor topography for the significant Group by Chord interaction (green regions in panel A) reveals a cluster of right-hemispheric channels over the parietal cortices. D) Post-hoc analysis of the Group by Chord interaction. The channel subset shown in C was used to extract the PLF values (within-group mean +/- SD) for each chord category.
Fig 5.
Main effect of Chord on PL (2-way ANOVA, p < .01; FDR-corrected) induced by musical chords.
A) Significant main effect of Chord is observed in the 20–40 Hz and 40–75 Hz bands, between 100 and 450 ms after stimulus onset (TFR thresholded as in Fig 4). B) TFRs of PL, separately for each chord type, averaged over subjects. Note that the color scale is intentionally chosen to emphasize mid-range PL values (red). C, above). The sensor topographies (above) in selected TF-ROIs (dashed boxes in A) for which at least 2% of TF-elements exhibited significant effects (p < .01; FDR-corrected). The main effect of Chord was observed predominantly in the right-hemispheric sensors in both ROIs. C, below). Post-hoc analysis of the PL values (mean over subjects +/- SD) in the TF-regions in A and sensor selection in C (above) indicates that the observed effect is caused by PL of population oscillations to the periodic amplitude envelope fluctuation of the dissonant chord (see also Fig 1).