Investigating human visual processing using MEG and psychophysics

Yuan, Jing 2022. Investigating human visual processing using MEG and psychophysics. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Our visual system organises sensory inputs into coherent object percepts. Knowledge and expectations about objects facilitate perceptual organisation via top-down processing. My PhD set out to investigate the neural mechanisms underpinning this process via frequency-tagging. Frequency-tagging studies embed flickers of different frequencies in a stimulus to drive narrow-band neural responses, which provide indices of spatial integration across the stimulus. My pilot experiments failed to robustly evoke this neural signature of perceptual organisation. Consequently, I conducted the following two lines of research. In a series of MEG studies, I systematically investigated the power of flicker-evoked neural responses as a function of stimulation frequency (Chapter 2). The resulting temporal response tuning profile showed substantial individual variability, which I assessed in relation to two other intrinsic properties of the individual’s visual system (Chapter 3). Spectral features of the temporal tuning profile were found to be associated with an individual’s perceptual temporal resolution but not with the peak frequency of visually-induced gamma oscillations. Moreover, the temporal resolution was found to be unrelated to visual gamma oscillations and the computationally modelled synaptic properties underlying visual gamma (Chapter 4). These MEG studies provide insights into dynamical properties of the visual system and form the methodological basis for future frequency-tagging studies. Besides the MEG research, I conducted a psychophysical study to investigate the top-down modulation of the perception of low-level features in an organised percept (Chapter 5). I found that whether the perceptual sensitivity to a low-level feature is enhanced by top-down processing depends on whether this feature contributes to the object percept. Future studies can investigate this effect further via frequency-tagging, by implementing flickers in the stimuli of the psychophysical task and choosing tagging frequencies informed by my MEG studies, to advance our understanding of the neural mechanisms underlying top-down processing in perceptual organisation.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Cardiff University Brain Research Imaging Centre (CUBRIC) Psychology
Date of First Compliant Deposit:	4 April 2023
Last Modified:	05 Apr 2023 10:24
URI:	https://orca.cardiff.ac.uk/id/eprint/158373

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