Effects of multisensory interactions on how subsequent sensory inputs are processed remain poorly understood. We investigated whether multisensory interactions between rudimentary visual and auditory stimuli (flashes and beeps) affect later visual processing. A 2 x 3 design varied the number of flashes (1 or 2) with the number of beeps (0, 1, or 2) presented on each trial, such that '2F1B' refers to the presentation of 2 flashes with 1 beep. Beeps, when present, were synchronous with the first flash, and pairs of stimuli within a trial were separated by 52 ms ISI. Subjects indicated the number of flashes presented. Electrical neuroimaging of 128-channel event-related potentials assessed both the electric field strength and topography. Isolation of responses a visual stimulus that was preceded by a multisensory event was achieved by calculating the difference between the 2F1B and 1F1B conditions, and responses to a visual stimulus preceded by a unisensory event were isolated by calculating the difference between the 2F0B and 1F0B conditions (MUL and VIS, respectively). Comparison of MUL and VIS revealed that the treatment of visual information was significantly attenuated approximately 160 ms after the onset of the second flash when it was preceded by a multisensory event. Source estimations further indicated that this attenuation occurred within low-level visual cortices. Multisensory interactions are ongoing in low-level visual cortices and affect incoming sensory processing. These data provide evidence that multisensory interactions are not restricted in time and can dramatically influence the treatment of subsequent stimuli, opening new lines of multisensory research.