Simultaneous presentation of auditory and visual input can often lead to visual dominance. Most studies supporting visual dominance often require participants to make an explicit response, therefore, it is unclear if visual input disrupt encoding/discrimination of auditory input or results in a response bias. The current study begins to address this issue by examining how multimodal presentation affects discrimination of auditory and visual stimuli, while using a passive oddball task that does not require an explicit response. Participants in the current study ably discriminated auditory and visual stimuli in all unimodal and multimodal conditions. Furthermore, there was no evidence that visual stimuli attenuated auditory processing. Rather, multimodal presentation sped up auditory processing (shorter latency of P300) and slowed down visual processing (longer latency of P300). These findings are consistent with research examining modality dominance in young children and suggest that visual dominance effects may be restricted to tasks that require an explicit response.