Date of Award
Open Access Dissertation
Multisensory integration (MSI) refers to the neural processes that integrate information from multiple different sensory systems and follows three established principles: the spatial, temporal and inverse effectiveness principles. Evidence now suggests that MSI can occur at the earliest stages of sensory processing in primary sensory cortices, including audiovisual integration in primary visual cortex; however, the mechanism responsible for audio-visual MSI enhancements remains elusive. Recently, unimodally presented sounds have been shown to activate visual cortex; however, no research has been conducted to evaluate if these sound-evoked responses reflect the auditory contribution to audiovisual integration in primary visual cortex. Here we conducted a series of three studies in which we systematically evaluated whether sound-evoked responses in visual cortex operated in a manner consistent with the principles of MSI by manipulating different auditory stimulus features while neural activity was recorded using an electroencephalogram (EEG). In the first study (Chapter 2), two experiments were conducted in which sound location was manipulated to allow us to evaluate if sound-evoked responses had the necessary spatial specificity to result in MSI in visual cortex. We observed a novel early-latency event-related potential (ERP) in primary visual cortex, the rapid occipital auditory-evoked response (ROAR) that satisfied both the spatial and temporal rules, and showed that the established late-latency sound-evoked response, the auditorily-evoked contralateral occipital positivity (ACOP), failed to meet the spatial and temporal principles. Chapters 3 and 4 manipulated sound intensity and frequency, respectively, to evaluate if the two observed sound-evoked responses operated in a manner consistent with the principle of inverse effectiveness. The ROAR displayed inverse effectiveness to sound intensity, but not to sound frequency, whereas the ACOP did not display inverse effectiveness to either sound intensity or sound frequency. Taken together we believe our results indicate that the ACOP does not reflect a mechanism of audiovisual integration in visual cortex, while the ROAR satisfies all three integration principles and likely plays a causal role in audiovisual integration within primary visual cortex.
Mac Adams, S. L.(2019). Sound-Evoked Activations of Visual Cortex and the Principles of Multisensory Integration. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/5605