“…In humans, most research work on multisensory integration is still at the stage of demonstrating the phenomenon and understanding the operative factors at perceptual and behavioral levels (for review, see O'Hare, 1991;Welch & Warren, 1986). Most frequently investigated are the aspects related to intersensory bias, that is, the capacity of a sensory system to modify-enhance, degrade-the perception from another system (e.g., Bernstein, 1970;Hershenson, 1962;Hubbard, 1966;McGurk & MacDonald, 1976;O'Leary & Rhodes, 1984;Sekuler, Sekuler, & Lau, 1997) and the relationships between this bias and multimodal spatial processing (how the sensory signals compete with one another according to the relative spatial position of the unimodal cues) (Bertelson & Radeau, 1981;Ehrenstein & Reinhardt-Rutland, 1996;Fisher & Pylyshyn, 1994;Frens, Vanopstal, & Vanderwilligen, 1995;Held, 1955;Pick, Warren, & Hay, 1969;Shelton & Searle, 1980;Stein, Meredith, Huneycutt, & McDade, 1989;Warren, McCarthy, & Welch, 1983) or the relationships between intersensory bias and the subject's attentional focus (Bernstein, 1970;Miller, 1982Miller, , 1986Spence & Driver, 1997). In these investigations, the tasks have been most often to detect, localize, and/or react to stimuli containing cues from one or more sensory modalities.…”