Tactile enhancement of auditory detection and perceived loudness.

To study the effects of touch on auditory processing, we examined whether uninformative and irrelevant tactile stimuli presented together with task-relevant sounds can improve auditory detection (Experiment 1), and enhance perceived loudness (Experiment 2). We demonstrated that irrelevant tactile signals facilitate the detection of faint tones, and increase auditory intensity ratings. These crossmodal facilitation effects were found for synchronous when compared to asynchronous auditory-tactile stimulation, and were stronger for weaker than for louder sounds. They are interpreted in terms of a multisensory integration mechanism that increases the strength of auditory signals, and adheres to the rules of inverse effectiveness and temporal (but not spatial) co-occurrence. This integration might be mediated by auditory-tactile multisensory neurons in regions of auditory association cortex that are also involved in auditory detection and loudness discrimination.