Palpable City

Palpable City is an extension of Tactile Space - a wearable interface to tactile landscapes, undertaken as part of my MS thesis project in Information and Computer Science in the Arts, Computation and Engineering program at University of California Irvine, 2004 - 2005



Palpable City explores the relationship between the abstract and concrete spaces of the city by parameterizing its spaces of representation–the space of architects and urban planners–with phenomenal space, to challenge our "lust to be a viewpoint" [1] in understanding the urban experience. The project allows walkers to feel the spatial form of the urban grid at their location as vibro-tactile rhythms on their body. The rhythms of the urban grid are parameterized by local conditions as the walker encounters them, reflecting the influence of time, light, temperature and humidity on the experience of space. Augmenting the everyday activity of walking the city with a tactile experience challenges participants to think about the interrelation of vision and touch in their experience of space. The void of purely optical space is thickened with palpable sensations, creating a tactile space that can only be explored by moving through it. Tactile displays are usually applied to provide orientation information in unusual phenomenal environments, such as virtual reality, deep sea diving, and zero gravity environments. In Palpable City, this process is reversed; instead of providing a stable spatial reference in unusual conditions, the technology is used to make the usual experience of space unusual.

1. Michel de Certeau. The Practice of Everyday Life, "Walking the City."


from TactileSpace installation at UC Irvine




There are a number of tactile receptors that could be stimulated for use in wearable computing applications: thermal, pressure, electrocutaneous, humidity, air movement, vibrotactile, etc. The current state of the art points to vibrotactile as the modality for ubiquitous computing applications. Vibrotactile actuators are neither intrusive nor painful (problems that are possible with electrocutaneous actuators). They can be felt through clothing, are inexpensive, and have relatively low mechanical and power requirements.

A perceptual illusion, sensory saltation, holds promise for use in vibrotactile displays. Sensory saltation occurs across the senses resulting in the perception of apparent motion. Tactile sensory saltation was discovered in the early 1970s by Dr. Frank Geldard at the Princeton Cutaneous Communication Lab. In a typical setup for eliciting tactile sensory saltation, three mechanical stimulators are place equidistant from each other on the forearm. The stimulator closest to the wrist delivers three short pulses, followed by three more at the middle stimulator, and finally three more at the last stimulator. Instead of perceiving three pulses at each of the stimulator sites, the observer perceives that all of the pulses are distributed with approximately uniform spacing from the site of the first stimulator to the site of the third. (Figure 2) The sensation is described as if a tiny rabbit was hopping up the arm from wrist to elbow, and is sometimes called the "rabbit" effect or the "cutaneous rabbit." (Figure 1) An important feature of this illusion is that it is able to simulate higher spatial resolution than the actual number of stimulators, yet create the impression of a dense stimulator array, thus potentially reducing the overall weight and power consumption needs of a wearable device.

Using variations in these parameters in different spatio-temporal patterns has uncovered a group of concepts which can be perceived through the tactile sense. For example, a single point can be perceived as a direction. (van Erp, 2001) Tactors arranged spatially on the body can create a relationship akin to vision where the ego center is perceived as one point and the stimulus at another, thus creating direction. Taking advantage of sensory saltation, lines can be perceived, as can their length, straightness, spatial distribution and smoothness. (Cholewiak, 2000) There is also some more recent research (TNO Human Factors) that suggests planes and three dimension forms can be perceived. Tactors on the body can create a 360 degree "field of touch" where lines and forms can be perceived not just on the surface of the body, but through the body. Finally, the tactile systems that have been discussed are very easy for users to learn, and require practically no training.

Figure 1: A Norwegian artist's illustration of the 'cutaneous rabbit'

Figure 2: Graphical representation of the saltation illusion


tactile vision+haptic space arises out of concerns about the ways in which new technologies shape our perceptions of space. The computer arises from Western scientific ideology which is built upon the assumption that the mind is separated from the body. The influence of this assumption is present at all levels of the technology, from the architectural level in the hardware/software split to the reduced set of body senses/movements engaged by its interface. The majority of research in human computer interaction has focused on the visual or aural modalities. Very little has been focused on the cutaneous senses. This could be because culturally, the senses of the flesh are regarded as the most lowly, the most animal. They are the farthest away from pure reason or thought, a belief upon which computing is founded: the mind/body split. The mind/body split has been debunked time and time again from all angles: philosophy, linguistics, biology, neurology, cognitive science, art, and even computer science (Dourish). However, embracing what embodiment means is difficult in a language that reifies the ideology. We talk of "my hand" or "my head" as if they are objects that we own, not inseparable parts of our being. To describe what is meant by embodiment, we must use neologisms such as the embodied mind, being-in-the-world, the life-world, etc. An embodied perspective that is not clouded by traces of duality is difficult, at best, in contemporary Western culture. In computer science, where the ideology is ingrained in the technology itself, it presents an even stiffer challenge.

As computing produces increasingly influential cultural artifacts and becomes ingrained in culture, it can no longer disregard the ideologies that have been responsible for cultural production for the thousands of years of humanity's existence. The 'arts' (with a lowercase 'a') have traditionally emphasized body knowledge in the making of things. Embodied thought is important in the design of physical spaces (architecture) as well as in the making of objects. As computing begins to shape physical spaces and their uses, it will be important to look to the arts and architecture to see where the underlying assumptions inherent in the discipline conflict with embodied humanity. tactile vision+haptic space combines technology and the environment through embodied interaction.

Please refer to the written thesis for citations: [pdf]

How to display a flying dragon, from Johann Kestler, Physiologia Kircheriana Experimentalis, p. 247. from

© Erik Conrad 1998-2006