Purpose: The aim of this review is to analyze haptic sensory substitution technologies for deaf, blind and deaf–blind individuals. Method: The literature search has been performed in Scopus, PubMed and Google Scholar databases using selected keywords, analyzing studies from 1960s to present. Search on databases for scientific publications has been accompanied by web search for commercial devices. Results have been classified by sensory disability and functionality, and analyzed by assistive technology. Complementary analyses have also been carried out on websites of public international agencies, such as the World Health Organization (WHO), and of associations representing sensory disabled persons. Results: The reviewed literature provides evidences that sensory substitution aids are able to mitigate in part the deficits in language learning, communication and navigation for deaf, blind and deaf–blind individuals, and that the tactile sense can be a means of communication to provide some kind of information to sensory disabled individuals. Conclusions: A lack of acceptance emerged from the discussion of capabilities and limitations of haptic assistive technologies. Future researches shall go towards miniaturized, custom-designed and low-cost haptic interfaces and integration with personal devices such as smartphones for a major diffusion of sensory aids among disabled.

We present a tactile telepresence system for real-time transmission of information about object stiffness to the human fingertips. Experimental tests were performed across two laboratories (Italy and Ireland). In the Italian laboratory, a mechatronic sensing platform indented different rubber samples. Information about rubber stiffness was converted into on-off events using a neuronal spiking model and sent to a vibrotactile glove in the Irish laboratory. Participants discriminated the variation of the stiffness of stimuli according to a two-alternative forced choice protocol. Stiffness discrimination was based on the variation of the temporal pattern of spikes generated during the indentation of the rubber samples. The results suggest that vibrotactile stimulation can effectively simulate surface stiffness when using neuronal spiking models to trigger vibrations in the haptic interface. Specifically, fractional variations of stiffness down to 0.67 were significantly discriminated with the developed neuromorphic haptic interface. This is a performance comparable, though slightly worse, to the threshold obtained in a benchmark experiment evaluating the same set of stimuli naturally with the own hand. Our paper presents a bioinspired method for delivering sensory feedback about object properties to human skin based on contingency–mimetic neuronal models, and can be useful for the design of high performance haptic devices.

The integration of polymeric actuators in haptic displays is widespread nowadays, especially in virtual reality and rehabilitation applications. However, we are still far from optimizing the transducer ability in conveying sensory information. Here, we present a vibrotactile actuator characterized by a piezoelectric disk embedded in a polydimethylsiloxane (PDMS) shell. An original encapsulation technique was performed to provide the stiff active element with a compliant cover as an interface towards the soft human skin. The interface stiffness, together with the new geometry, generated an effective transmission of vibrotactile stimulation and made the encapsulated transducer a performant component for the development of wearable tactile displays. The mechanical behavior of the developed transducer was numerically modeled as a function of the driving voltage and frequency, and the exerted normal forces were experimentally measured with a load cell. The actuator was then tested for the integration in a haptic glove in single-finger and bi-finger condition, in a 2-AFC tactile stimulus recognition test. Psychophysical results across all the tested sensory conditions confirmed that the developed integrated haptic system was effective in delivering vibrotactile information when the frequency applied to the skin is within the 200–700 Hz range and the stimulus variation is larger than 100 Hz.

During the last decade significant advances have been made in vibrotactile actuator design that are leading to the development of novel haptic technologies. Similarly, important innovations have been made in the area of virtual reality for scene rendering and user tracking. However, the integration of these technologies has not been well explored. In this paper, we outline a broad design philosophy and integration plan of these tools. In addition, we give an overview of applications for such a cohesive set of technologies. Preliminary results are provided to demonstrate their critical importance and future widespread use.