Vision merges with touch in a purely tactile discrimination.

To construct a coherent percept of the world, the brain continuously combines information across multiple sensory modalities. Simple stimuli from different modalities are usually assumed to be processed in distinct brain areas. However, there is growing evidence that simultaneous stimulation of multiple modalities can influence the activity in unimodal sensory areas and improve or impair performance in unimodal tasks. Do these effects reflect a genuine cross-modal integration of sensory signals, or are they due to changes in the perceiver's ability to locate the stimulus in time and space? We used a behavioral measure to differentiate between these explanations. Our results demonstrate that, under certain circumstances, a noninformative flash of light can have facilitative or detrimental effects on a simple tactile discrimination. The effect of the visual flash mimics that produced by a constant tactile pedestal stimulus. These findings reveal that sensory signals from different modalities can be integrated, even for perceptual judgments within a single modality.