Sherman, Maxine (2016) Prior expectations shape subjective perceptual confidence. Doctoral thesis (PhD), University of Sussex.

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Abstract

The notion that unconscious Bayesian inference underlies perception is gaining
ground. Predictive coding approaches posit that the state of the world is inferred
by integrating, at each level of the perceptual hierarchy, top-down prior beliefs
about sensory causes and bottom-up prediction errors. In this framework,
percepts correspond to a top-down stream of beliefs that best 'explain away'
sensory signals. Although such frameworks are gathering empirical support,
subjective facets of perception remain unexplained from these perspectives.
This thesis combines behavioural, computational and neuroimaging methods to
examine how subjective visual confidence can be accounted for in a predictive
coding framework.
Experiment one shows that, behaviourally, perceptual expectations about target
presence or absence both liberalise confidence thresholds and increase
metacognitive accuracy. These results are modelled in a signal detectiontheoretic
framework as low-level priors shifting the posterior odds of being
correct. Using EEG, experiment two reveals that influence of expectations on
decision and confidence oscillates with the phase of pre-stimulus alpha
oscillations. This means that prior to target onset, both objective and subjective
decisions have been rhythmically biased by the periodic recruitment of
expectations to visual areas. Using fMRI, experiment three shows that in the
post-stimulus period, expectations and sensory signals are integrated into
confidence judgements in right inferior frontal gyrus (rIFG). Furthermore, this
process recruits orbitofrontal cortex and bilateral frontal pole, which represent
top-down influences, and occipital lobe, which represents bottom-up signals.
Together, these results suggest that expectations shape subjective confidence
by biasing the posterior probability of the perceptual belief.

Item Type:	Thesis (Doctoral)
Schools and Departments:	School of Psychology > Psychology
Subjects:	Q Science > QZ Psychology
Depositing User:	Library Cataloguing
Date Deposited:	27 Oct 2016 10:10
Last Modified:	27 Oct 2016 10:10
URI:	http://srodev.sussex.ac.uk/id/eprint/64934

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