Metrical Rhythm Implicitly Orients Attention in Time as Indexed by Improved Target Detection and Left Inferior Parietal Activation
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■ When we direct attentional resources to a certain point in time, expectation and preparedness is heightened and behavior is, as a result, more efficient. This future-oriented attending can be guided either voluntarily, by externally defined cues, or implicitly, by perceived temporal regularities. Inspired by dynamic attending theory, our aim was to study the extent to which metrical structure, with its beats of greater or lesser relative strength, modulates attention implicitly over time and to uncover the neural circuits underlying this process of dynamic attending. We used fMRI to investigate whether auditory meter generated temporal expectancies and, consequently, how it affected processing of auditory and visual targets. Participants listened to a continuous auditory metrical sequence and pressed a button whenever an auditory or visual target was presented. The independent variable was the time of target presentation with respect to the metrical structure of the sequence. Partici-pantsʼ RTs to targets occurring on strong metrical positions were significantly faster than responses to events falling on weak metrical positions. Events falling on strong beats were accompanied by increased activation of the left inferior parietal cortex, a region crucial for orienting attention in time, and, by greater functional connectivity between the left inferior parietal cortex and the visual and auditory cortices, the SMA and the cerebel-lum. These results support the predictions of the dynamic attending theory that metrical structure with its relative strong and weak beats modulates attentional resources over time and, in turn, affects the functioning of both perceptual and motor preparatory systems. ■
