Sensory and integrative properties of the fast visuomotor system

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Humans are largely visual animals; vision is the main sense we use to identify objects of interest in our external world. In order to execute accurate visual actions, visual information from the outside world needs to be rapidly contextualized and integrated with current body posture to generate efficient and appropriate motor commands. Previous research has shown that such contextualization and integration can be carried out remarkably quickly by a fast visuomotor system capable of initiating a movement in less than 150 ms of a visual event (e.g., such as a corrective action to catch a falling cup of water). Precise recordings of neck and limb muscle activity have provided evidence for stimulus-locked responses (SLR), which are small bursts of muscle activity well in advance of movement onset that occur time-locked ~80-100 ms after visual stimuli.Our hypothesis is that SLRs are a signature of the fast visuomotor system mediated through the superior colliculus, a key midbrain structure for orienting.******The goal of the proposed research is to better understand the fast visuomotor system by examining the SLR in upper limb muscles, as humans execute planar reaching movements. In the first of two projects, we aim to better understand the sensory properties of the SLR. To date, the SLR has been elicited by simple punctate visual stimuli presented in isolation. Here, we will investigate the SLR following the presentation of more refined visual stimuli (e.g., varying spatial frequencies, providing stimulus motion), or complex environments (e.g., presenting multiple stimuli, or varying initial position of the eyes and hand). The findings from this project will provide information about the visual processing and pathways underlying the SLR.***In the second project, we will study the integrative properties of the SLR while participants reach in different behavioural contexts. For example, the SLR will be studied when participants move away from a stimulus, abruptly cancel an upcoming action, move in an altered visual-to-motor environment, or make a decision between uncertain alternatives. Together, the results from this project will provide functional insights into how the SLR relates to ensuing behaviour, and reflects the participant's cognitive state in a variety of different tasks.***The overall objective of this proposal is to better understand the SLR from both a sensory perspective, as the results from project 1 will provide information about the extent and timing of visual processing, and a functional perspective, as the results from project 2 will clarify how the SLR relates to ensuing behaviour. One of the particularly unique aspects of the SLR is that it is available on a trial-by-trial basis in humans; accordingly, we can leverage many of the tools normally reserved for animal neurophysiology to better understand the contribution of the fast visuomotor system to human behaviour. ********