When primates make decisions about sensory signals, their choices are biased by the costs and benefits associated with different possible outcomes. However, much remains unknown about the neuronal mechanisms by which reward information is integrated into the perceptual decision-making process. I used electrophysiological, psychophysical and imaging techniques to explore the effect of reward on sensory representations, whilst humans and monkeys made perceptual judgements about structure-from-motion (SFM) stimuli. Electrical microstimulation of visual area V5/MT in the macaque monkey was used to bias per- ceptual judgements, under different available reward sizes for correct choices. The behavioural effect of microstimulation interacted with available reward, and, in the context of a drift diffu- sion model of decision-making, the results demonstrated that reward must influence sensory processing before visual signals and micro stimulation signals are accumulated in sensorimotor areas. In a parallel human psychophysics experiment, viewers made decisions about SFM stim- uti whilst their choices were biased towards one outcome or the other by unequal pay-offs. A full drift -diffusion model was fitted to human choice and reaction time data. There was a signif- icant effect of reward on model drift rate, a parameter known to be dependent upon evidence represented in sensory brain regions. A second set of experiments used magneto encephalography (MEG) to explore activity in visual , areas in human cortex and the effects of reward. Brain responses to retinotopic visual stimuli were localized with three different MEG source analysis methods, and localization accuracy was evaluated by comparison with fMRI maps obtained in the same individuals. The results demon- strated that the beamformer and minimum norm estimate (MNE) methods were most suitable for investigating early visual activity with MEG. Human brain activity was then recorded with MEG whilst viewers made perceptual judgements about SFM stimuli, under unequal pay-offs. The results revealed an effect of reward size on early MEG responses in the region of the occipi- tal cortex and visual precuneus. Taken together, the experiments presented in this thesis provide consistent evidence that in- formation about reward can influence the processing of sensory information during perceptual decisions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:589747 |
| Date | January 2012 |
| Creators | Cicmil, Nela |
| Contributors | Krug, Kristine ; Parker, Andrew |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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