Visual-tactile integration: does stimulus duration influence the relative amount of response enhancement?

Responses to multiple stimuli from different modalities tend to be faster compared to responses to each of these stimuli alone. Neurophysiological studies on higher mammals and behavioral studies on humans suggest that the relative amount of enhancement is inversely related to stimuli intensity. In two experiments the duration of visual and tactile stimuli was varied to investigate whether duration, as a further determinant of stimulus effectiveness, is also inversely related to the relative amount of response enhancement. Visual and tactile stimuli were presented left or right of fixation either in the same or different hemifields. Participants were required to gaze only at visual stimuli and to ignore tactile (focused attention paradigm). Saccadic reaction times were recorded. Results from both experiments show that the relative amount of response enhancement was largest for the shortest stimulus duration and decreases with increasing stimulus duration, i.e., inverse effectiveness of stimulus duration.