Supervisor: Profs Tim Ledgeway and Paul McGraw
School: Psychology

Description:

Transcranial magnetic stimulation (TMS) is a popular method for studying the functional properties, connectivity and chronometry of brain regions associated with vision. However comparatively little is known about the precise mechanisms by which TMS influences on-going visual processing, though previous studies suggest it may suppress the processing of the signals associated with a task and/or induce increased levels of internal noise. We have recently shown that although repeated TMS stimulation over area V1 initially impairs performance on a simple orientation judgement task, accuracy levels unexpectedly improve across a block of 200 trials (but no recovery occurs if a brief, external, visual noise mask is used instead of a TMS pulse). The computational principles underlying this recovery are currently unknown, but an interesting possibility is that the visual system can dynamically adapt to increased internal noise levels, by increasing the temporal interval over which visual stimuli are integrated, thus minimising the deleterious effects of TMS-induced cortical activity on sensory judgments. This project will explore these important issues.

Required skills:

• Demonstrable programming experience in a language such as Matlab or Python and an interest in understanding vision.

Desirable skills:

• Previous experience with behavioural (psychophysical) experiments, and computational modeling

Background readings:

• Harris, J. A., Clifford, C. W. G., & Miniussi, C. (2008). The functional effect of transcranial magnetic stimulation: Signal suppression or neural noise generation? Journal of Cognitive Neuroscience, 20, 734-740.
• Ledgeway, T., Heslip, D & McGraw, P. (2015). Changes in temporal integration mitigate the disruptive effects of transcranial magnetic stimulation over visual cortex in humans. Journal of Vision, 15(12): 809; doi:doi:10.1167/15.12.809
• Ruzzoli, M., Marzi, C. A., & Miniussi, C. (2010). The neural mechanisms of the effects of transcranial magnetic stimulation on perception. Journal of Neurophysiology, 103, 2982-2989.
• Stevens, L.K., McGraw, P.V., Ledgeway, T. & Schluppeck, D. (2009). Temporal characteristics of global motion processing revealed by transcranial magnetic stimulation. European Journal of Neuroscience, 30, 2415-2426.

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