Our senses are an interface with the world. Each sense adds a level of immersion in how we experience reality. Remove or alter even one sense and your perception of reality differs. A dolphin in the ocean can perceive creatures and objects in the sea from great distances, while I’m limited to just a few meters with what I can see and hear. Fundamentally, nothing is different about our environment, but the way I perceive that reality compared to the dolphin is vastly different. Our perceptions shape different realities.
Touch is, perhaps, the most important form of perception for humans. In previous articles, we’ve described how touch is made up of four modalities: tactile, vibration, thermal, and force. Removing any one of the modalities of cutaneous feedback alters how you experience touch, and hence, reality. Imagine for a moment closing your eyes and performing each of the following activities. Take away any one of the modalities of touch, and you can see how it would affect your interpretation of reality.
Skin and the Anatomy of Touch
Our skin is a pretty amazing organ. I mean, aside from protecting us from just about everything, it is just as important in crafting a reality as our sense of sight, sound, smell, and taste. The somatic sensory system is at the foundation of our skin’s ability to perceive stimuli like pressure, texture, temperatures, pain, and proprioception—the position and motion of the body’s joints and muscles. To deliver our sense of touch, a set of specialized nerve cells operate as touch receptors and are broadly divided into two groups: mechanoreceptors and thermoreceptors.
Mechanoreceptors are responsible for most of what you experience from touch, but not all mechanoreceptors are created equal. Different kinds of mechanoreceptors are located across the body, and each has a different function, rate of adaptation (how fast the receptor responds to a stimulus), and threshold of activation (at what point a stimulus causes the receptor to respond). The four mechanoreceptors most important to touch—the Meissner's corpuscles, Pacinian corpuscles, Merkel's disks, and Ruffini's corpuscles—are located in the glabrous (hairless) skin, and all have low thresholds of activation, meaning they are some of the most sensitive receptors. When you feel the purr of a cat or your skin stretching as you grip your hand around a glass jar—that’s your mechanoreceptors at work. Your thermoreceptors, the result of free nerve endings, then tell you the glass is cold or the cat is warm.
Collectively, these receptors account for most of the tactile, thermal, and vibration feedback you experience. What about force? Another set of mechanoreceptors—muscle spindles, Golgi tendon organs, and joint receptors—handle that business. Continuing with the exercise above: It’s these cells that tell you you’re petting a cat and not a hedgehog.
What’s really amazing is that these receptors, along with a host of other receptors unassociated with touch, such as chemoreceptors, photoreceptors, nociceptors, almost entirely shape how you perceive the world around you.
Editing Our Touch Experiences
When we bring haptics into virtual reality, though, what we touch no longer is bound to what we see. In “normal” reality, a cat always feels like a cat. With virtual reality and realistic haptics, one could make a porcupine feel like a cat. Or a cold glass of water could feel hot. Or a dog could purr. These examples show us two things. First, to create realistic experiences, it’s important that our visual cues in VR map to equivalent haptic experiences to avoid the uncanny valley of touch. Second, it reveals the amazing creative capabilities when you bring lifelike touch to VR. For decades, artists have used a range of shapes and colors for creating surreal imagery. A cat can be green, blue, purple, have tentacles and six legs, or appendages in any other configuration thanks to the flexibility of the visual medium.
Yet never have we had the capability to create haptic experiences that aren’t representative of what our eyes see. I recently experienced WeVR’s The Blu, in which I sat on the ocean floor surrounded by a curtain of glowing jellyfish. What if, instead of reaching out and feeling a slimy membrane (or feeling nothing at all), I could instead feel a sensation like the caress of fern fronds or the purr of a cat?
The realization of technology capable of delivering realistic and complex haptic feedback is like going from having a Kodak camera to having a digital camera with photoshop. We’ve unlocked a palette of tools, filters, and colors, all of which are unfettered from reality. In VR, we can edit not only the reality you can see, but also the reality you can feel.
I think that’s pretty exciting.