Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Corneil, Brian D


Humans and other primates rely heavily on vision as a primary sensory input to drive our upcoming volitional motor actions. Our motor system makes so many of these visual-to-motor transformations that they become ubiquitous in our daily lives. However, a central question in systems neuroscience is how does the brain perform these transformations?

Reaching movements have been an ideal model for studying volitional motor control in primates. Broadly, these visually-guided reach movements contain three inherent sensorimotor components: an action selection component, a motor execution component, and a motor learning component. A core assumption is that as reach movements become more complex, our motor system requires more cortical processing, which prolongs the time between stimulus onset and reach initiation. Typically, visually-guided reach movements occur within 200-300 ms after the onset of a visual stimulus.

Previous human behavioural studies have shown that prior to these volitional reach movements, a directionally-tuned neuromuscular response can also be detected on human upper limb muscles within 100 ms after the onset of a novel visual stimulus. In this thesis, I characterized the sensorimotor properties of this visual stimulus-locked response (SLR), under the same framework that has been used to describe volitional motor control.

In Chapter 2, I showed that the SLR is an ‘automatic’ motor command generated towards the visual stimulus location regardless of the current task demands. In Chapter 3, by changing the initial starting hand position and the pre-planned reach trajectory, I showed that like volitional control, the pathway mediating the SLR can rapidly transform the eye-centric visual stimuli into a proper hand-centric motor command. In Chapter 4, I showed that the directional tuning of the SLR is influenced by motor learning. However unlike volitional control, the SLR is only influenced by the implicit, but not explicit, component of motor learning. Thus, the results from this thesis suggest that despite the reflexive nature of the SLR, the SLR shares some sensorimotor properties that have been classically reserved for volitional motor control.