Melbourne School of Psychological Sciences - Theses
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ItemThe temporal dynamics of neural processing of static and moving objects( 2023-01)Transmission and processing of information takes time. In the case of motion perception, the brain could theoretically compensate for these delays by using information about a moving object's past trajectory to predict where the object is located at the present moment. This thesis aimed to explore the neural delays that accumulate during visual processing in humans, and whether these can be compensated during perception of objects moving with a predictable trajectory. In Study 1, we used forward encoding modelling of EEG data to show that, after onset of a simple, static stimulus, the spatial specificity of the neural representation of the stimulus fluctuated over time. This indicates that stimulus processing unfolds in a series of feedforward and feedback sweeps of neural activity through regions of the visual cortex consisting of neurons with varying receptive field sizes. Following this, in Study 2, we again used multivariate analysis of EEG data to investigate the neural response to moving stimuli, to discover whether the brain extrapolates the position of moving objects to compensate for neural delays. We found that objects moving into a position on the screen were represented in that location much earlier than if they were flashed in the same position. This predictive encoding of position served to fully compensate for the delays that accumulate during early stimulus processing. Finally, in Study 3, we investigated the consequences of compensation for delays on perception. In the High-Phi illusion, uncorrelated noise textures are interpreted as motion due to a rotating inducing texture; we show that perception of illusory motion can be explained by extrapolation of the preceding motion. Furthermore, the perceived position of a flashed static object was biased by these predictive signals, and the magnitude of illusory motion jumps and position shifts scaled with the speed of the inducing motion. Overall, these results show that processing even simple visual information takes time, but this time can be compensated when viewing predictable visual motion, leading to changes in neural coding and perception of moving objects.