Effect of reward on visual perceptual decision-making in humans and non-human primates

Thesis

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 perceptual 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 diffusion model of decision-making, the results demonstrated that reward must influence sensory processing before visual signals and microstimulation signals are accumulated in sensorimotor areas. In a parallel human psychophysics experiment, viewers made decisions about SFM stimuli 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 significant 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 magnetoencephalography (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 demonstrated 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 occipital cortex and visual precuneus.

Taken together, the experiments presented in this thesis provide consistent evidence that information about reward can influence the processing of sensory information during perceptual decisions.

Authors: Cicmil, N

• Publication date: 2012
• DOI: 10.5287/ora-eqpe7apv8
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: decision-making; perception; vision; neuroscience; cortex; reward
• Subjects: Neuroscience; Cognitive Neuroscience; Computational Neuroscience