Using hallucinations to understand top-down processes in human vision.

Tessa Dekker (primary)
Experimental Psychology & Institute of Ophthalmology
University College London
Jeremy I Skipper (secondary)
Experimental Psychology


In addition to sensory inputs, the visual cortex receives large amounts of feedback (top-down signals) from other cortical areas. This feedback plays a crucial functional role for percepts when sensory signals are noisy, ambiguous, or complex, which can be uncovered in visual illusions [1]. In some instances, top-down signals can give rise to rich and realistic visual experiences in the case of hallucinations. This occurs with high prevalence in people with severe vision loss but otherwise neurologically healthy (Charles Bonnet Syndrome) [2], and can be induced artificially via perceptual deprivation and hallucinogenic substances in controls [3,4,5]. How these experiences differ from each other and normal vision, and how and why they emerge, is currently poorly understood. The aim of the PhD is to investigate internally-driven visual percepts in health and eye disease, by investigating how brain activation (using MRI and EEG) and perceptual experiences (using psychophysics and self-report) during vivid, internally-driven vision differ from those during normal vision in terms of neural dynamics and information processing in visual cortex.


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Animal disease, health and welfare
Area of Biology
Techniques & Approaches
Image ProcessingMathematics / StatisticsSimulation / Modelling