Wearable technologies for haptic feedback

The present thesis deals with the the development and testing of novel feedback strategies for providing tactile sensory information to human subjects in a non-invasive manner, towards the assessment of whether and how external haptic feedback can be quasi-naturally embodied within the human sensorimotor scheme for sensory substitution and augmentation purposes. Bioinspired haptic feedback strategies have been implemented and tested, towards a discrete-event encoding of tactile information. Specifically, the encoding strategy enables the real-time conversion of force information into neuronal spikes by means of the Izhikevich model. In such a novel approach, the spikes, usually provided via neuronal electric stimulation directly to nerves to restore tactile sensation in amputees or to investigate how tactile information is encoded in the brain, are presented on the skin surface mechanically. Scientifically, the proposed approach aims at merging together the simplification mechanisms of the discrete event-driven sensory feedback control (DESC) policy with the possibility of conveying qualitatively rich haptic information. A novel tele-palpation apparatus for the real-time transmission of information about object stiffness to the human fingertips was developed. Such a telepresence system consisting of a mechatronic sensing platform, for the automatized indentation of samples, and a haptic display, for the remote delivery of tactile information, allowed to encode object stiffness into spike trains at a proper frequency through a neural model. Experimental tests were carried out to investigate the mechanisms of tactile perception and the feasibility of the neuromorphic-based feedback strategy in enabling stiffness identification in telepresence and passive touch conditions. Further, the effectiveness of the proposed bioinspired method based on contingency–mimetic neuronal models for the provision of sensory feedback about object properties to human skin was also investigated in allowing nodule identification in telepresence and active touch conditions. A stand-alone, self-powered, wireless haptic system consisting of a sensing module and a haptic interface was designed and developed, being conceived for sensory substitution and augmentation purposes in rehabilitation and prosthetics. According to different neuromorphic-based and DESC-based feedback strategies, data on specific gait events or on the foot-ground interaction were used to trigger the activation of the haptic display motors along the waist by modulating the vibrotactile stimulation strength (frequency, amplitude, or both). The haptic feedback system was used to provide ipsilateral vibrotactile feedback in a protocol involving intact subjects to assess candidate strategies to be adopted in clinical trials. The potential of the more sophisticated and informative encoding strategy (the neuromorphic-based one) was further investigated in another context, in which the feedback was used to provide information also about terrain features for enabling identification of even and uneven terrains in both healthy subjects and lower limb amputees, respectively. The effectiveness of the haptic feedback system in conveying gait event-related information in the form of discrete short-lasting vibrotactile stimulations was also exploited in clinical settings for rehabilitation purposes. In this scenario, three transfemoral amputees performed a short training program based on over-ground walking aided by real-time bilateral rhythmic cues to enhance temporal gait symmetry.