Understanding the timing of incoming neural signals is fundamental to moving, speaking and perception. To properly determine causality, animals must judge motor-sensory signals with the correct timing. However, this is not an easy task for brains to solve, because signals carried by different sensory modalities are processed at different speeds. The problem of sensory delays is compounded by factors ranging from changing lighting conditions to limb growth. This suggests that the brain continually recalibrates its motor- sensory timing judgments. Our preliminary studies seem to confirm this: we make the novel demonstration that an artificially injected delay between actions and effects leads to a recalibration of temporal order judgments. Under some circumstances this leads to an illusory reversal of action and effect. The goal of this proposal is to elucidate how the brain determines causality, and how it dynamically recalibrates that determination when the timing of feedback changes. We employ a battery of techniques including novel psycho physics, Virtual Reality and fMRI. We have four aims: (SA1) Demonstrate and quantify the conditions under which brains recalibrate motor-sensory timing. To this end, we have developed novel psychophysical experiments to analyze the effect of injected delays on temporal order judgments. (SA2) Determine the neural basis of causality timing judgments using fMRI. (SA3) Explore the neural basis of causality recalibration using fMRI and computational theory. (SA4) Root these findings in the context of timing in the brain more generally. Throughout the proposal, novel psychophysical findings are buttressed by brain imaging, and both sets of results steer our understanding of the neural mechanisms. Collectively, these experiments shed light on the dynamic temporal interactions of motor-sensory systems, leading to new insights about disorders that might be properly understood as disorders of temporal calibration.
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