Neurocognitive signatures of auditory and visual sensory gating

The aim of this thesis was to investigate the neurophysiological phenomenon of auditory and visual sensory gating, and primarily, explore the notion of a cross-modal mechanism. The electrophysiological characterisation and associated cognitive functions of both visual and auditory sensory gating were examined to determine similarities and differences across the two input modalities. In order to explore this, three issues were addressed: 1) The latency and surface scalp location(s) of the maximal or most reliable sensory gating was identified; 2) the associated cognitive mechanism(s) were explored using 11 diverse tasks incorporating attentional inhibition; 3) the sensitivity of the gating mechanism was examined with regards to changes in stimulus form/location or changes in attentional demand. Despite limited consideration in the literature to date, this thesis reports evidence that sensory gating is a phenomenon that exists within the visual modality and moreover, can be reliably observed. Compared to standard auditory gating procedures, visual gating is found at a later latency and further back in the central-parietal or central-occipital electrode sites. Correlations between visual and auditory gating with latent inhibition and the continuous performance task suggests gating, independent of iii modality, may reflect the encoding of target and non-target stimuli/stimulus features alike, and the subsequent categorisation and inhibition of those deemed irrelevant. Additionally, a comparable limitation was observed for both modalities, with regards to sensitivity of sensory gating, with spatial features being processed as a priority over the perceptual stimulus features. In conclusion, the differences in latency and component of the observed gating presented in this thesis, indicates that visual and auditory sensory gating are not products of the same intra-cortical mechanism. Rather the gating observed in each modality is a functionally distinct mechanism that is qualitatively analogous across modalities.