Our brain has a limited in capacity for processing concurrent information streams. While the limitations of processing capacities have been extensively studied within the visual modality, less is known about how processing capacities are limited across sensory systems. Using EEG, we investigated how auditory stimuli modulate the processing of visual input at early perceptual stages. Participants were asked to detect brief deviant visual or auditory stimuli while viewing a continuous steady-state visual stimulation. Both visual and auditory stimuli elicited a desynchronization of the steady-state visual evoked potentials (SSVEPs) between 300~500ms following the transient event. These results suggest that early visual cortex activity is subject to both within-modality and between-modality competition.