A few evenings ago, on a country road, I came upon two pickup trucks stopped in the middle of the road, their drivers chatting with each other. I had been riding for several hours; a friend had come up from Los Angeles for the day to ride the area with me, and we had gone down to Jalama Beach for lunch – he had the celebrated burger, I had its less well known vegan alternative. Getting past the trucks meant riding onto gravel. As I rode past them, the front wheel slipped slightly for a moment, then bit as it regained grip, and I returned to the asphalt.
I did not see the slip happen. The tire’s contact patch is not visible from the saddle, and I only became aware of the movement through a change in the forces at the handlebars as the front wheel moved around. The correction was immediate: my hands had already straightened the bars, and my understanding of what had happened landed only once the wheel had gripped and I was back on the asphalt. I was tired after several hours of riding, my concentration was slipping, but I made it almost automatically.
I’m not always comfortable about the bike moving around underneath me, a feeling that derives from a crash I had on a dirt bike in Spain many years ago, when the bike didn’t just move around, it nearly went off a cliff. A story for another time.
As I reflected on that moment in the Santa Ynez Valley, I began to think about how the body and machine are one as we move along the road; it’s something I wrote about extensively in my PhD thesis, the hybrid combination of rider and motorcycle. That arrangement, in which a person’s contact with the world is mediated through an object they have learned to trust, is of course much older than the motorcycle, and it’s about to change dramatically. Technology shifts will force the motorcycle industry to completely reinvent the experience of mechanical feedback as drivetrains shift to electric motors, and if the engineers doing the reinventing are to be successful, they will likely benefit from an understanding of some other fascinating examples of how humans have been augmented and hybridized with objects.
The rein
Prior to the invention of the internal combustion engine, for most of recorded history the fastest thing a person could ride was a horse, and the primary channel of communication with the animal was a strip of leather. The rein is an unusual instrument in that it connects two nervous systems, transmitting in both directions: the rider’s hands issue instructions through it, and the horse’s mouth, neck and gait report back through the same channel. An experienced rider reads the animal’s attention, its anxiety, and the ground it is moving over from tension in the leather. Equitation science now measures rein forces directly[1]; the instruction is ancient, for Xenophon’s treatise on horsemanship, written in the fourth century BC, already advises that the horse’s mouth should be pulled neither so harshly that the animal tosses its head nor so gently that it feels no pressure [8].
The cane
Philosophy approached the same subject by way of the blind person’s cane. Maurice Merleau-Ponty, writing in 1945, observed that for a skilled user the cane stops being an object that is perceived and becomes an instrument that perception happens through: “The blind man’s cane has ceased to be an object for him, it is no longer perceived for itself; rather, the cane’s furthest point is transformed into a sensitive zone, it increases the scope and the radius of the act of touching and has become analogous to a gaze”[2]. The user does not feel wood against the palm, they feel the pavement at the tip of the stick. Michael Polanyi made the same observation about tools generally in 1958: “We pour ourselves out into them and assimilate them as parts of our own existence”[3]. The cane demonstrates something the rein only implies. When a sense is absent, a trusted object can carry a substitute channel, and with sufficient practice the substitution disappears from awareness.
Laboratory work later established how far this capacity can extend. From the late 1960s, Paul Bach-y-Rita’s sensory substitution experiments fed camera images to grids of vibrating pins pressed against the skin of blind subjects; with training, subjects reported perceiving objects out in the world rather than sensations on their backs[4]. The general lesson drawn from this line of work is that the nervous system, given a reliable channel of communication, will adopt it as a sense.
The vest
The rein and the cane both transmit real forces. The third object in this history is the one I find most interesting, as it does something categorically different.
Historically, military aviation has had a problem that the ordinary senses could not solve. In cloud, at night, or under sustained acceleration, the inner ear delivers false information about which way is up, and spatial disorientation has been a persistent cause of fatal accidents throughout the history of powered flight; one published analysis argues that it contributes to nearly a third of all aircraft mishaps[5]. It’s similar to a phenomenon with which scuba divers will also be familiar, the feeling of weightlessness leading to disorientation, referred to in that case as “being in the blue”. It’s an almost blissful state of sensory deprivation in which one loses all sense of direction and space, a state that I recall with equal parts fondness and terror from my Divemaster training many years ago.
In the 1990s a US Navy flight surgeon named Angus Rupert began developing the Tactile Situation Awareness System: a vest fitted with an array of small vibrating units, called tactors, that deliver the aircraft’s attitude to the pilot’s torso, so that information ordinarily read from instruments arrives through the skin. If the aircraft banks left, the tactors on the left side fire, and so on.
No mechanical connection runs from the wing to the tactor; instead, a computer decides what each vibration should mean and where to deliver it. The trials covered both helicopters and fixed-wing aircraft, and demonstration flights showed that pilots could learn the code to the point of total reliance. In Rupert’s words, reporting the trials in 2000: “Pilots were able to fly complex maneuvers with no instruments or outside visual references (blindfolded) with less than 20 min of training”[6].
The motorcycle
The motorcycle belongs at the latter end of this hybridization history. A combustion motorcycle transmits rather than encodes: the vibration in the bars and pegs, the sound rising and falling with engine speed, the lash in the driveline, and – in my case the other day – the forces returned through the front tire, are physical byproducts of the machine working, and the rider learns to read them the way riders once read the horse through the rein. None of it was designed exclusively as a message, and while it can be desirable to engineer vibration out of the mechanical object, absolute elimination is not achieved in practice.
An electric drivetrain produces little vibration and little sound, and that disrupts this longstanding arrangement. Whatever signals the rider is given to read will increasingly be chosen by engineers and delivered deliberately, working in a similar way to the pilot vest’s tactors. Discussions about synthetic sound and haptic feedback are usually conducted alongside arguments about authenticity of the riding experience. Notwithstanding that, the historic examples above suggest an evolution towards a more precise question: whether riders will extend to designed, synthesized signals the trust they built on mechanically transmitted ones.
The evidence from other fields is that they can. The vest-clad pilots flew without sight on coded vibration; similarly, prosthetics research over the past decade has shown that adding sensory feedback to an artificial limb measurably increases the wearer’s sense that the limb is part of their own body[7]. The success of adoption appears to depend on the reliability and consistency of the channel rather than on its origin: a well-designed signal can be learned quickly, as the TSAS training figure shows, whereas the deeper incorporation the prosthetics studies measure, the sense that the device belongs to the wearer’s body, develops over extended use.
That last point seems to me the one the motorcycle industry ought to hold onto. Designed feedback can clearly carry trust; the cane, the vest and the prosthetic limb each achieved that threshold for users. Whether any particular designed signal earns the same trust from motorcyclists will soon be put to the test as manufacturers inevitably transition to electric drivetrains. Riders developing trust in their machine is a complex, visceral process, and it presents some deep challenges for designers.
Ride safe.
Tim
References
- Dumbell, L., Lemon, C., Williams, J. (2019). “A systematic literature review to evaluate the tools and methods used to measure rein tension.” Journal of Veterinary Behavior 29, 77–87.
- Merleau-Ponty, M. (1945). Phénoménologie de la perception. Paris: Gallimard. Quotation from the English translation by Donald A. Landes, Phenomenology of Perception (London: Routledge, 2011), p. 144 (p. 178 in the French original).
- Polanyi, M. (1958). Personal Knowledge: Towards a Post-Critical Philosophy. Chicago: University of Chicago Press, p. 59 (“Skills,” on tools and probes).
- Bach-y-Rita, P., Collins, C.C., Saunders, F.A., White, B., Scadden, L. (1969). “Vision substitution by tactile image projection.” Nature 221, 963–964.
- Gibb, R., Ercoline, B., Scharff, L. (2011). “Spatial disorientation: decades of pilot fatalities.” Aviation, Space, and Environmental Medicine 82(7), 717–724.
- Rupert, A.H. (2000). “Tactile situation awareness system: proprioceptive prostheses for sensory deficiencies.” Aviation, Space, and Environmental Medicine 71(9 Suppl), A92–99. Quotation from the published abstract. PubMed.
- Shehata, A.W., Rehani, M., Jassat, Z.E., Hebert, J.S. (2020). “Mechanotactile Sensory Feedback Improves Embodiment of a Prosthetic Hand During Active Use.” Frontiers in Neuroscience 14:263; and “Grasping Embodiment: Haptic Feedback for Artificial Limbs.” Frontiers in Neurorobotics (2021) 15:662397.
- Xenophon. On Horsemanship (Peri Hippikēs), fourth century BC. Translated by H.G. Dakyns; Project Gutenberg ebook 1176. Chapters VII and X cover the bit and the management of the horse’s mouth (“The horse’s mouth is not to be pulled back too harshly so as to make him toss his head aside, nor yet so gently that he will not feel the pressure”).