Multisensory integration has been recently shown to produce a larger pupil size than unisensory constituents. Superior colliculus (SC), an important laminar nucleus in the midbrain, not only engages in spatial attention and saccadic eye movements, neurons in whose intermediate layer can also modulate pupil size. Given neurons in the deeper layers of SC are able to integrate multimodal signals, it is thus assumed that the multimodal inputs, relative to unimodal stimuli, may modulate pupil size as well.