Our primary mode of interaction with computers has long been visual. From the onset of the first terminals through modern personal computers, we receive most of our information via the screen. While we have long been receiving information through speakers and sound generators, the onset of the “sound-only” computer (virtual home assistants), has only recently started to become ubiquitous. There is however a field of human-computer interaction that is still in its infancy – touch. Where we control almost all aspects of our machines with touch, the action is rarely returned. The concept of haptic feedback, first developed in the 80s, has long been stagnant and limited to notification and touch-feedback purposes on mobile phones.1 This paper outlines new technologies, advancements, and uses in the field of haptic technology in a rapidly expanding tech world.
Somatosensation is much more than the sensation of touch. With thermoreceptors for heat, nocireceptors for pain, mechanoreceptors for touch, proprioceptors for orientation, and many others, our skin allows us to experience the wide range of somatosensory experiences including heat, pain, texture, moisture, and more.1 With such a wide range of receptors, artificial stimulation of them, known as haptic feedback, has an uncanny valley problem of its own to solve. With current technologies, there is a formidable challenge to overcome to accurately portray a lifelike, convincing sensation to a human.
The concept of haptic feedback, or artificially generating a sense of touch, was first realized with vibration. Short vibrations allow users to bring a device or an event to their attention, and are still methods well in use today. Mobile phones with touch screens employ short haptic events upon key depression, to alert the user that they have depressed a key successfully. Mobile phones, smart watches, and many other devices vibrate to alert the user to a particular event that requires their attention. As it is an incredibly useful and versatile tool, vibration shows no likely sign of disappearing from our technology any time soon. It does however have a major shortfall; it does not have the capability to replicate somatosensory events in the same way as other technologies, the most promising being electrical stimulation. Quite simply, vibration will always be felt by the brain as vibration.
The use of varying types of electrical stimulation is paramount in the advancement of this technology, and is poised to expand rapidly. With different frequencies, amplitudes, and pulse lengths, it is entirely possible to stimulate every type of somatosensory end-receptor or nerve.2 The sensation of touch is primarily generated through the use of transcutaneous electrical nerve stimulation (TENS), a technique normally used to block peripheral nerves in pain management therapy.2 Percutaneous solutions have been employed in the past, but due to the invasive nature and the use cases (putting on and taking off a suit), transcutaneous solutions are well preferred.2 With TENS, tactile feedback can be simulated with surface electrodes; by varying frequency, amplitude and pulse length, current systems can cause tickling to painful sensations.4, 2
Neuromuscular electrical stimulation (NMES, or MES), has been used in the past for muscle training, or offsetting the effects of atrophy in para/quadriplegic patients.2 It is seeing a new role however in the generation of pseudo-haptic events in a similar manner to TENS.2 Whereas TENS can trigger tactile sensations, the use of NMES has the ability to create a sense of force or pressure on the user, by creating “voluntary, but not self-induced muscle contractions” as stated in Kruijff et al.2 By using high intensity, low frequency pulses, NMES can cause the excitation and activation of alpha motor neurons, exciting musculature and creating a sensation of force or pressure.2 These stimuli can be increased in amplitude, allowing for the recruitment and activation of more neurons and therefore muscles.2
Traditional TENS and MES requires the specific attachment and placement of transcutaneous adhesive electrodes on a patient’s skin.2 In order to be a viable, reusable solution however, this technology has evolved to transmit electrical impulses directly to a patient’s skin via the suit or device, so that it can be easily gowned or removed. Older technologies have sewn leads and wires into the suit, where newer technologies like the Teslasuit have been experimenting with conductive polymers and modular solutions.1
With the rapid expansion of virtual reality (VR) technology, uses of haptic feedback suit technology have been rapidly expanding and entering the market. VR is not however the only use for these kinds of suits. There is great benefit in medical rehabilitation, spaceflight orientation, and situational awareness, as discussed below.
VR technology has exploded within the last few years, allowing users to completely immerse themselves in convincing foreign environments. Gaming is the primary use of VR, but recent innovations have shown it to be useful for uses beyond gaming. Current commercial VR solutions employ both audio and visual stimuli to convince a user that they are immersed in a virtual environment. As the market currently stands, innovations in haptic feedback and touch are being developed as separate systems with the ability to connect to individual games through software development kits (SDKs).1 Several commercial solutions are currently in beta testing and developmental stages, with a few poised to release over the coming year. A few of the top innovators include the Teslasuit (with no relation to Tesla motors), HaptX gloves, and KOR-FX, a haptic vest similar to the Teslasuit, the first two discussed in detail below.1
The Teslasuit markets itself as a modular immersive suit for virtual reality gaming. Using conductive polymers as the primary structure, and specific add on modules, the suit can actively stimulate heat, cold, vibration, and tactile stimulation, through various electrical modules and modes.1 Employing functional electrical stimulation, muscular electrical stimulation, and transcutaneous electrical nerve stimulation, the suit has the ability to create senses of touch, pressure, and even almost-painful stimuli.1, 4 Current iterations of the technology use 16 channels (comprised of 4-6 leads), with a pulse amplitude of 0-80mA, and frequencies ranging from 1 to 500Hz.5 High frequency stimulation has been described by early users as a sharp poking sensation, whereas low frequency stimulation has been described as a tickling, or skin crawling sensation, with various other sensorineural experiences between the two frequencies.4
Using an older technology redeveloped for the digital age, HaptX gloves focus specifically on a user’s hands, and achieve different sensations with micropneumatics and microfluidics.8 With small valves and silicon actuators, HaptX gloves are able to deliver a wide range of sensations, textures, and temperatures to a user’s hands, allowing them to feel a wide variety of objects in virtual reality.8 An old trick with a new twist, this technology is arguably more expensive to produce than electrodes, making it suitable for highly sensitive areas like the hands. Whereas small silicon actuators on the inside of the gloves cause the sensation of touch, a microfluidic network of capillaries runs through the gloves, allowing water to flow generating feelings of hot and cold temperatures.8
Another exciting innovation of Haptic Feedback Suit technology is in the augmentation and treatment of neurovestibular pathologies.1 In recent experiments, patients with neurovestibular conditions were subjected to a random tilt platform, and balance and gait was studied.7 When patients were subjected to haptic feedback in an anterioposterior direction as tilt was applied, balance scores improved dramatically.7 This evidence suggests that a Haptic Feedback Suit can be paired with a series of accelerometers to help those suffering from these conditions to regain some semblance of a normal life during neurovestibular episodes.7 Interestingly enough, these pathologies closely mimic the experiences of those in no or microgravity environments (pilots and astronauts), so research for rehabilitation and for spaceflight often draws parallel conclusions and happens simultaneously.1
One of the more important challenges with flight and spaceflight is spatial disorientation. Pilots train specifically and extensively on conflicting vestibular and visual conflicts, as consequences of misinterpreting a sense can often be disastrous. The use of haptic feedback in flight and spaceflight environments can provide a sense of orientation, and in some cases guidance.1, 6 These technologies allow a pilot to better and more quickly respond to events (“feeling the aircraft”), as well as provides a sense of touch allowing for better spatial orientation and situational awareness.1
The TSAS is a wrap-around belt and seat cushion system originally envisioned in the 1980s that is still being experimented with today.1,6 The concept provides a level of situational awareness to a pilot of an aircraft by relaying an aircraft’s pitch and roll (via onboard avionics) to the pilot with vibrotactile stimulators.6 Two specific companies are working on various iterations of the technology, but the overall concept includes a firewall mounted control panel, an umbilical attached belt-seat-avionics cushion connection, and onboard suit actuators and control units (to allow for redundancy and compensation in case of actuator malfunction).6
Field tests of the TSAS have allowed helicopter pilots to successfully hover a helicopter without the use of vision, a near-impossible concept without the technology due to the unreliability of the vestibular system.6 Problems currently being worked through include suit weight due to the actuators and control units, and the umbilical wiring.6 Wireless alternatives like Bluetooth technology are currently being explored by both companies, but response time and dropped packets remains a formidable challenge.6 Aviation is not the only environment that could benefit from this technology. Astronauts, divers, firefighters, and others whose sense of orientation and vision is often obscured, have been theorized to benefit from a haptic feedback suit that provides orientation. Some prototypes have been recently exploring these fields, addressed below.
The ESNOS system is a prototype system comprised of an array of coin vibratory motors, a touch interface system for the wearer, a Bluetooth monitor, and a 3 axis accelerometer.1 The suit is designed to be used by a wearer, and a 3rd party providing orientation directions by means of haptic feedback through a user interface.1 The 3rd party presses a button indicating forward, and the wearer feels a vibration in the front of their suit.1 This has been indicated to be of particular use in environments where vision is severely limited, such as during extravehicular activities (spacewalks), while diving, or by use of firefighters.1
It can be assumed that the ultimate goal of the virtual reality field is to immerse the user in a world that is indistinguishable from true reality. The addition of tactile sensation and touch to an already convincing and well-developed experience only further serves to immerse users in this environment. It is likely haptic feedback suits will expand to incorporate not just tactile sensations, but heat, cold, weight, resistance, pressure, proprioception, pain, and all other aspects of the human touch experience.
Looking to the future, this technology is poised to disrupt the virtual reality market and add the next level of the user experience. Ethical questions do arise though in the ability for these devices to inflict pain on their users. What steps will be taken to ensure device security, could this technology pose lethal for those with undiagnosed arrhythmias, and will this technology be implemented in our day to day lives, are all questions that need to be raised looking towards the future.
While haptic feedback suit technology has the potential to directly benefit those with sensorineural conditions and those in environments that cause sensorineural conflict, it is likely we will see the biggest advances coming from the ever growing field of virtual reality.