Separating rhythms of sensory and motor preparation

Covert attention enhances the processing of relevant stimuli within our environment without the need for overt eye movements. Recent work has demonstrated that our covert attentional system rhythmically samples the environment approximately 3 to 8 times per second. Our sensory system must work in tandem with our motor system to produce fluent natural behaviour. That is, once we perceive a task-relevant stimulus, we must execute the appropriate response. Although past work has shown an important role for actions in resetting perceptual sampling, it remains unclear to what extent motor preparation is itself rhythmically modulated. To investigate whether motor preparation follows a similar rhythmic sampling as found in perception, we designed a task that orthogonalized sensory and motor preparation. Compound cues indicated both the most likely location of an upcoming target stimulus (left or right visual field) and the most likely motor response (left or right button press). Both sensory and motor predictions of cues were valid in a majority of trials. However, in a minority of trials, predictions could be invalid in only the sensory domain, only the motor domain, or both domains with equal likelihood. The interval between the cue and target varied between 300 and 1100 ms. This manipulation allowed us to interrogate the effects of valid sensory vs. motor cues orthogonally time. Consistent with previous work we found that sensory cues modulated behaviour in a range between 3 and 8 Hz. In contrast, interestingly, motor preparation showed little evidence of rhythmic modulation.