Investigation of Rapid Visual Feedback Processing

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Balalaie, Parsa
Visually-guided reaching , Online correction , Interception task , Electromyography , Reaction time , Stimulus-locked Response(SLR)
The human brain can generate rapid motor responses in less than 100 ms when responding to visual stimuli. The earliest wave of these responses can be time-locked to the stimulus onset (Stimulus-locked Response, SLR) rather than the movement itself. Previous work highlights that these responses are generally more prevalent under predictable conditions, such as when there are visual cues on where the stimulus will occur, but little else is known about the behavioral contexts that influence these rapid motor responses. To investigate this, we employed a fast-feedback interception task (FFIT) in which the participants intercepted a virtual target moving towards them in the workspace. In some trials, the target randomly jumped laterally to the left or right at different times, limiting the time available to generate a motor correction in order to modify the urgency to respond. In another series of experiments, we varied the proportion of trials in which the target did not jump, modifying the certainty of whether they would need to make a correction or not. We also recorded electromyographic activity from shoulder and elbow muscles during the task. When the target always jumped, 97% of participants elicited SLRs within 100 ms of the jump. When the target jump occurred later (less time to respond), reaction times were faster, the onset of the SLR was earlier, and the magnitude of the SLR was larger. We also found that the onset time of the SLR was faster, and its magnitude was larger when there was a higher probability that the target jump would occur. In the second experiment, jumps with different times to respond were combined in the same blocks with different proportions of jump trials. We found that co-contraction of agonist and antagonist muscles emerged as a common strategy when participants were given very limited time (~250ms) to intercept the target following the jump. However, including trials in which the target did not jump (increased uncertainty) reduced co-contraction of the arm muscles. Our results highlight that SLRs are more prevalent under more predictable conditions and when motor corrections must be extremely fast to attain the behavioral goal.
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