Figure 1.

Two potential varieties of multisensory interactions assessable by applying a linear model to the analysis of event-related potentials. The linear model involves comparing the summed responses from unisensory conditions with the response to the multisensory stimulus. In this figure, the level of activity (arbitrary units) within fictive brain regions is illustrated within the blue discs. In panel (A) modulations in response strength are illustrated, wherein the same set of brain regions is observed in response to the summed unisensory and multisensory conditions, albeit with greater magnitude in the latter case. This is illustrative of a supra-additive gain modulation. The colored topographic maps illustrate what one might observe in the ERP data. In panel (B) modulations in the configuration of brain regions active under multisensory stimulus conditions are illustrated, such that brain regions otherwise inactive under unisensory conditions are observed. In terms of event-related potential analyses, this latter mechanism would manifest as a modulation in the topography of the electric field at the scalp, which is illustrated in the voltage maps below. It should be noted that these two mechanisms, i.e., gain and generator modulations, can co-occur.