Intensity-dependency and plasticity of perceived audio-visual simultaneity: behavioural and neural correlates

Horsfall, Ryan
(2021) Intensity-dependency and plasticity of perceived audio-visual simultaneity: behavioural and neural correlates. PhD thesis, University of Liverpool.

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The perception of simultaneity and temporal order of audio-visual stimuli is vital in understanding which sensory information emanates from the same physical events. Two tasks commonly used to assess the relative perceptual latencies of audio-visual stimuli are the simultaneity judgement and temporal order judgement tasks, both of which provide an estimate of the point of subjective simultaneity (PSS), which reflects the temporal stimulus offset (typically in milliseconds) where simultaneity is perceived. These two estimates, perhaps surprisingly, have been shown to be uncorrelated, leading to the suggestion that the two tasks are mediated by separate neural mechanisms. The present thesis addresses this possibility using electroencephalography (EEG), and demonstrates that task-based differences are evident only late in the event-related potential, attributable to differences in decisional, rather than early sensory, processes. The PSSs estimated using these tasks are highly variable and depend on the relative intensity of the stimuli. By comparing various contender models, the author argues that the effect of intensity on the PSS can be explained by intensity-dependent processing latencies, and critically, that this intensity dependency is consistent across the two tasks. Furthermore, the current thesis highlights a novel process, whereby the PSS shifts depending on the visual intensity (as well as the leading modality) of the preceding trial, which is argued to reflect a decisional mechanism to compensate for differences in central arrival times caused by intensity-dependent processing latencies. Finally, training observers using the SJ task has previously been cited as a potential method to improve the accuracy of audio-visual perceptual judgements in those with multisensory deficiencies. The presented data highlights the lack of generalisability of training induced performance improvements between audio-visual stimuli with two visual intensities, highlighting limitations of these proposed interventions.

Item Type: Thesis (PhD)
Divisions: Faculty of Health and Life Sciences
Depositing User: Symplectic Admin
Date Deposited: 06 Jul 2021 13:01
Last Modified: 09 Nov 2021 08:52
DOI: 10.17638/03128890