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The great majority of the world's music is metrical, i.e., has periodic structure at multiple time scales. Does the metrical structure of a non-isochronous rhythm improve synchronization with a beat compared to synchronization with an isochronous sequence at the beat period? Beat synchronization is usually associated with auditory stimuli, but are people able to extract a beat from rhythmic visual sequences with metrical structure? We addressed these questions by presenting listeners with rhythmic patterns which were either isochronous or non-isochronous in either the auditory or visual modality, and by asking them to tap to the beat, which was prescribed to occur at 800-ms intervals. For auditory patterns, we found that a strongly metrical structure did not improve overall accuracy of synchronization compared with isochronous patterns of the same beat period, though it did influence the higher-level patterning of taps. Synchronization was impaired in weakly metrical patterns in which some beats were silent. For the visual patterns, we found that participants were generally unable to synchronize to metrical non-isochronous rhythms, or to rapid isochronous rhythms. This suggests that beat perception and synchronization have a special affinity with the auditory system.

We analyzed a set of full-head (66 channels, CTF Inc.) magnetoencephalography (MEG) data recorded when 5 subjects performed rhythmic right index-finger flexion and extension movements on the beat (synchronization) or off the beat (syncopation) with a visual metronome at 1 Hz. Neuromagnetic activities in the alpha (8-14 Hz), beta (15-30 Hz) and gamma (30-50 Hz) ranges were shown to correlate with different aspects of the task. Specifically, we found that, compared with the control condition in which subjects only looked at the visual metronome without making any movement, all the movement conditions were accompanied by a decrease of power in the alpha range (8-14 Hz) in sensorimotor channels of both hemispheres, and an increase of coherence among a subset of these channels. The same comparison showed that power changes in the beta range differentiate task conditions by exhibiting power increases for synchronization and power decreases for syncopation. Changes in the gamma range power were found to be related to the kinematics of movement trajectories (flexion versus extension). These results suggest that three important cortical oscillations play different functional roles in a visuomotor timing task.

Spectral analysis was applied to study the variability in human rhythmic synchronization to a visual, auditory or combined auditory-visual metronome of about 2 Hz, as well as the variability in continuation tapping at the same rate with or without visual or auditory feedback. In synchronization, variability was larger in the visual condition than in the auditory and combined conditions, but only below frequencies of about 0.3 Hz. Thus, there seem to be at least two sources of variability in synchronization, one being modality-independent and limited to intervals shorter than 3 s, and the other being modality-dependent and evident as slow "drift", especially in the visual task. In continuation tapping, variability did not depend reliably on the presence or modality of feedback. However, spectral analysis revealed a change in the temporal structure of variability around 0.08 Hz (a period of about 12 s or 24 taps), which roughly agrees with earlier findings reported in the literature.

This paper presents evidence indicating that the signals generated by neural responses to visual input can be either enhanced by increasing or suppressed by decreasing the area of the stimuli to which attention is directed. We used magnetoencephalography (MEG) to measure the frequency-tagged steady-state visual evoked responses of 11 subjects presented with two superimposed images flickering at different frequencies. Each image consisted of seven parallel bars of equal length; in any image, all bars were either red or green and either horizontal or vertical. At randomly chosen times during the experiments, any one of the three middle bars in either image transiently increased or decreased in width. Subjects were asked to attend to one image and ignore the other and to respond to changes in bar width in the attended image with a key press. In one condition, subject responses were required for changes in any of the three central bars of the attended image. We found that visual steady-state evoked responses to the attended image were enhanced relative to those evoked by the unattended image in this condition. In a second condition, subject responses were required for changes only in the middle bar. In this condition, the responses to the attended image were suppressed relative to those of the unattended image. These results may reflect relative differences in the synchronization and desynchronization of responding neuronal populations. [ABSTRACT FROM AUTHOR]