Multisensory Integration

Our brain is constantly flooded by sensory signals from a number of different modalities; these signals must be integrated and attended to appropriately in order to create an accurate perception of our environment. When auditory and visual events occur simultaneously within close proximity to each other, though at disparate locations, source localisation for one modality interacts with that for the other modality in a characteristic manner (Bermant & Welsh, 1976) - referred to as cross-modal bias. The two locations are averaged with a greater weighting given to the stimulus with the greater spatial reliability, typically the visual stimulus. This results in the spatial location of the auditory stimulus appearing to be closer to the visual stimulus

An answer to the role of attention in multisensory integration could help determine whether this is a cognitive or automatic process, consequently this could lead to a greater understanding of how the brain forms a coherent representation of extra-personal space. This will result in a better understanding of the areas of the brain responsible for processing visual and auditory information. This research could also have implications for the understanding of multisensory integration deficits in neurological and psychiatric populations such as those with, schizophrenia (Ross et al., 2007) and autism (Magnee et al., 2010), as well as the aging population (Hugenschmidt,

(2000) who demonstrated that the apparent location of sound burst was attracted towards a visual event occurring simultaneously in a discrepant location; however they found that the size of this effect was unaffected by directing deliberate visual attention towards the location of the peripheral visual stimulus, suggesting that deliberate spatial attention plays little if any role. These findings were supported and further developed by Vroomen et al. (2001) who found a dissociation between automatic attention and apparent sound location, thus concluding that direction of attention has no affect on ventriloquism, suggesting that ventriloquism occurs at a stage of processing before attentional selection. Taken together, these findings appear to suggest no role for attention in multisensory integration. On the contrary, these findings fit with the alternative notion that the ventriloquist effect reflects automatic interactions between sensory codes for location and is pre-attentive and therefore unaffected by the direction of spatial attention. It makes functional sense for spatial interactions to be processed in a bottom-up fashion in order to ascertain the most accurate location of the stimuli in your environment irrespective of direction of attention from an evolutionary perspective. More recent research such as Talsma et al. (2010) has suggested however, greater