Enhancement of response times to bi- and tri-modal sensory stimuli during active movements.

Simultaneous activation of two sensory modalities can improve perception and enhance performance. This multi-sensory enhancement had been previously observed only in conditions wherein participants were not performing any movement. Since tactile perception is attenuated during active movements, we investigated whether a bi- and a tri-modal enhancement can occur also when participants are presented with tactile stimuli, while engaged in active movements. Participants held a pen-like stylus and performed bidirectional writing-like movements inside a restricted workspace. During these movements participants were given a uni-modal sensory signal (visual--a thin gray line; auditory--a brief sound; haptic--a mechanical resisting force delivered through the stylus) or a bi- or tri-modal combination of these uni-modal signals, and their task was to respond, by pressing a button on the stylus, as soon as any one of these three stimuli was detected. Results showed that a combination of tri-modal signals was detected faster than any of the bi-modal combinations, which in turn were detected faster than any of the uni-modal signals. These facilitations exceeded the "Race model" predictions. A breakdown of the time gained in the bi-modal combinations by hemispace, hands and gender, provide further support for the "inverse effectiveness" principle, as the maximal bi-modal enhancements occurred for the least effective uni-modal responses.