Amputees but not healthy subjects optimally integrate non-spatially matched visuo-tactile stimuli

Our brain combines sensory inputs to create a univocal perception, enhanced when stimuli originate from the same location. Following amputation, distorted body representations may disrupt visuo-tactile integration at the amputated leg. We aim to unveil the principles guiding optimal and cognitive-efficient visuo-tactile integration at both intact and amputated legs. Hence, we designed a VR electro-stimulating platform to assess the functional and cognitive correlates of visuo-tactile integration in two amputees and sixteen healthy subjects performing a 2-alternative forced choice (2AFC) task. We showed that amputees optimally integrate non-spatially matched stimuli at the amputated leg but not the intact leg (tactile cue at the stump/thigh and visual cue under the virtual foot), while healthy controls only integrated spatially matched visuo-tactile stimuli. Optimal integration also reduced 2AFC task reaction times and was confirmed by cognitive EEG-based mental workload reduction. These findings offer insights into multisensory integration processes, opening new perspectives on amputees' brain plasticity.