Visual and Auditory Perceptual Decision-Making in The Human Brain as Invesitgated by fMRI and Lesion Studies
by Ahmad M. Nazzal
Date of Examination:2017-05-26
Date of issue:2017-07-27
Advisor:Prof. Dr. Melanie Wilke
Referee:Prof. Dr. Melanie Wilke
Referee:Prof. Dr. Mathias Bähr
Persistent Address:
http://dx.doi.org/10.53846/goediss-6405
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Abstract
English
Perceptual decision-making refers to the act of choosing one option from a set of alternatives based on the available sensory information. In this manuscript, we used model-based functional magnetic resonance imaging and lesions studies to investigate auditory and visual perceptual decision-making. In the first study, we demonstrated that spatially-specific sensory evidence, when decoupled from motor plans, accumulates in modality-specific sensory cortices: Occipital regions showed signals correlated to spatially-specific accumulated visual sensory evidence, and superior temporal regions showed signals correlated with spatially-specific accumulated auditory evidence. On the other hand, signals in the frontal and parietal regions were modulated by the level of accumulated sensory evidence in a spatially non-specific manner for both modalities; when the level of evidence was low, the signal in the frontal and parietal regions was stronger regardless of the sensory modality. Thus, the well-known signatures of evidence accumulation observed in frontal and parietal cortices described in the literature might reflect secondary decision processes such as saliency. In the second study, we investigated the neural correlates of confidence in the decision. We used model-based fMRI to investigate the neural correlates of visual perceptual decision-making and devised criteria based on predictions from integrate-and-fire attractor models to identify neural correlates of confidence in the decision. We managed to disentangle the neural correlates of sensory evidence accumulation from neural correlates of decision monitoring; confidence in the decision and error detection. We found that the signal in the occipital cortex was modulated by visual sensory evidence accumulation while the frontal and midbrain regions had signals suggestive of decision monitoring. In the third study, we investigated the effect of cortical and subcortical lesions on auditory and visual perceptual decision-making. We formulated an fMRI-driven hypothesis based on the findings from our fMRI studies. We used voxel-based lesion-symptom mapping to investigate the role of lesions on patients' behavior in a voxel-by-voxel manner. Data from the patients suggests a role of the right parietal cortex in auditory task performance as predicted by the fMRI study. Together, our results help to reveal the neural correlates of auditory and visual perceptual decision-making in human beings, explore neural correlates of decision-monitoring, and provide insights into the underlying mechanisms of the auditory and visual hemispatial neglect syndrome.
Keywords: decision-making; fMRI; Auditory; Visual; hemispatial neglect syndrome; Evidence accumulation
