Multisensory interactions and impacts on attention and awareness

In our daily lives, we constantly receive input from multiple senses, including sights, sounds, odours, tactile sensations, and tastes. Information from one sensory modality may interact with, and affect the processing of, information from another sense, and stimuli from different senses may be integrated and perceived as one multisensory event. Multisensory stimuli have been argued to be particularly effective at capturing attention, and the overarching aim of the first part of this thesis was to investigate the proposed ‘special’ attentional status of external multisensory stimuli, and their effects on both attentional capture and awareness. Using well-established manipulations of perceptual load, multisensory stimuli presented as search targets were demonstrated to offer an advantage over unisensory stimuli. Whilst still being subject to modulation by visual perceptual load, this advantage presented both in terms of speed of detection (Chapters 2 & 5) and awareness (Chapter 4) and persisted even when the load itself was multisensory (Chapter 5). On the other hand, multisensory stimuli presented as irrelevant distractors were found to be no more distracting than unisensory stimuli (Chapter 2), and ERP evidence suggests that the two sensory modalities involved were actively suppressed through two independent processes, with no multisensory integration (Chapter 3). Additionally, multisensory stimuli do not appear to impose on perceptual capacity any differently than unisensory stimuli in a primary task (Chapter 5). The final study looks at a different type of multisensory interaction, in terms of the impact of internal mental imagery on external sensory Processing. Chapter 6 presents fMRI evidence of differing effects on early perceptual processing of visual and auditory external stimuli, by visual and auditory internal imagery. Theoretical and practical implications of all findings are considered throughout, and in Chapter 7.