Beat detection vs prediction
Perception of temporal patterns and regularities is critical for normal hearing, speech, motor control, and music processing. In the auditory domain, perception of a regular pulse, or beat, within a temporal pattern is associated with basal ganglia activity. Two alternative accounts of this striatal activity are possible: searching for temporal regularity in early stimulus processing stages, or internal prediction of the timing of future beats after the beat is already found. To resolve between these different accounts, we used fMRI to investigate neural activity in different stages of beat perception. Participants listened to a series of beat and non-beat (irregular) temporal sequences. For each beat sequence, the preceding sequence provided a temporal beat context for the following sequence. A beat sequence could be preceded by a non-beat sequence, requiring the beat to be found anew (‘beat-finding’ condition), or could be preceded by a beat sequence with the same beat rate (‘beat-continuation'), or a different rate ('beat-adjustment'). If the basal ganglia role is in detecting regular structure, activity should be greatest during 'beat-finding' sequences, whereas if they are involved in prediction, activity should be greatest during 'beat-continuation' trials. We found greatest activity for beat-continuation trials, less for beat-adjustment trials, and the least for beat-finding trials. Other motor areas did not show this graded activation pattern. Thus, the basal ganglia’s response suggests a role in beat prediction based on an internal model of the rhythm, not a role in extraction and analysis of temporal structure to find the beat.