Many studies have revealed that attention operates across different sensory modalities, to facilitate the selection of relevant information in the multimodal situations of every-day life. Cross-modal links have been observed either when attention is directed voluntarily (endogenous) or involuntarily (exogenous). The neural basis of cross-modal attention presents a significant challenge to cognitive neuroscience. Here, we used a neural network model to elucidate the neural correlates of visual-tactile interactions in exogenous and endogenous attention. The model includes two unimodal (visual and tactile) areas connected with a bimodal area in each hemisphere and a competition between the two hemispheres. The model is able to explain cross-modal facilitation both in exogenous and endogenous attention, ascribing it to an advantaged activation of the bimodal area on the attended side (via a top-down or bottom-up biasing), with concomitant inhibition towards the opposite side. The model suggests that a competitive/cooperative interaction with biased competition may mediate both forms of cross-modal attention. 1. Introduction Our environment constantly provides us a large amount of information. An important goal for the brain is to filter out irrelevant information and to select only relevant events in order to guide behaviour. A basic mechanism for selecting information is to process stimuli from a limited portion of space; this function is mediated by spatial attention. Most research on spatial attention has been focused on purely unimodal situations [1–5]. Most studies show that responses to stimuli presented at the attended locations increased in comparison to those at the unattended locations, both at behavioural and electrophysiological level. Moreover, extensive theoretical and experimental work on the visual system [1, 3, 6–9] has suggested an influential hypothesis about the neural mechanisms underlying visuospatial attention, known as the biased competition hypothesis. The basic idea is that attention biases the competition between multiple stimuli in the visual field in favour of one stimulus, so that neurons encoding the attended stimulus win the competition and suppress the activity of the cells representing unattended stimuli. The competition among concurrent stimuli can be biased both voluntarily, when the subject dedicates more attentional resources to a given spatial position (endogenous or top-down spatial orienting), or reflexively, when an external stimulus cue suddenly appears at a given spatial location (exogenous or bottom-up spatial
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