Abstract
We investigated visual and tactile motion perception and multimodal integration by measuring velocity discrimination thresholds over a wide range of base velocities and spatial frequencies. The stimuli were two physical wheels etched with a sinewave profile, one seen the other felt, allowing for the simultaneous presentation of visual and haptic velocities, either congruent or in conflict. Stimuli were presented in two separate intervals and subjects required to report the faster motion in 2AFC, using visual, tactile or bimodal information. Both visual and tactile and bimodalò thresholds showed a characteristic “dipper function”, with the minimum at a given “pedestal duration”. The “dip” (indicating facilitation) occurred over the same velocity range (0.05 - 0.2 cm/sec) at all spatial frequencies and conditions. Most interestingly, a tactile pedestal facilitated a visual test and vice versa, indicating facilitation between modalities. The facilitation occurred only for motion in the same direction, over a narrow range of velocities. It did not occur for neutral stimuli like sound beeps (ruling out reduction of temporal uncertainty), nor for motion in opposite directions, even when subjects knew that the motion was in the opposite direction (ruling out a “cognitive” facilitation”). This results suggest that visual and tactile motion signals pass through a common neural mechanism, allowing one to facilitate the other.
Supported by European Research COuncil “STANIB”.