A multisensory illusion with haptic interaction to treat phantom limb pain

Abstract

Phantom limb pain (PLP) is a chronic, intractable condition that affects over 2 million Americans. PLP has been treated by pharmaceuticals, and interventional treatments, as well as psychological strategies including sensory illusions. This work develops a theoretical framework to characterize prior instantiations of sensory illusions. Each instantiation is a particular treatment protocol that consists of three design elements: stimulus modality, volitional movement, and multisensory interaction. Utilizing this framework, we custom-built a haptics-enabled mirror visual feedback (MVF) sensory illusion. The device provides its amputee user with tactile and proprioceptive feedback, specifically the capability to interact with a 1 DOF haptic slider bar. In this way, we sought to incorporate additional sensory modalities into the illusion. In a case study with lower limb amputees (N=3), the realism of the device's seven illusions was evaluated. Preliminary results are that: 1) interaction with the haptic slider bar increased the amputee's sense of presence of the amputated limb, 2) one subject with intractable chronic PLP experienced relief that persisted during use of the device and reported tactile and proprioceptive sensation in the phantom limb, 3) forceful pressure against the slider bar produced asymmetric proprioceptive forces that interrupted the illusion, 4) the specific amputation site affected which illusions were most believable. These preliminary findings indicate that multi-sensory illusions may augment and enhance MVF instantiations, potentially improving the therapeutic value for a wider range of amputation cases.