Touch seems like a paradigm contact sense. In order to experience things through touch it seems necessary that we be in direct contact with them.
I argue that this is false. We can and often do experience things not in direct (or even apparent) contact with our bodies. We do this primarily by using tools and other intermediary devices that appropriately connect us to things in the distal world. I give many examples in the book to support this claim, and then describe several classes of distal touch.
Tactual Filling-In: Fanning your fingers apart, run your fingertips down a tabletop. You experience the unified and singular surface of the table as your hand moves. You do not feel the table only at the five points of contact; you experience one solid table.
Volume Touch: Volume touch was first discussed (as far as I know) by pioneering psychologist David Katz in 1925. Volume touch involves touching solid objects through thick mediating layers of cotton or other materials. Such experiences give the impression of a volume or space through which the distal object is perceived. The experience is distal, but occurs through some soft material which adds a sense of depth and space to our experience. A similar case is palpation. Doctors, therapists, and masseurs use palpation to sense such objects as tumors, cysts, and muscle knots which lie below the surface of the skin. In these cases there is an awareness of something not in direct contact with the body.
Indirect Touch: Similar to volume touch, indirect touch involves touching an object through a thin, non-spacious material, like a blanket or towel. We can touch a playful puppy hiding under a blanket, and determine its shape, size, location, and movements. In so doing, the blanket functions something like a medium through which we touch the puppy.
Tactual Projection: The paradigm case of distal touch.
Such cases involves experiences of objects and properties that are not in direct contact with the actual limits of our body, but are connected to us through an intervening tool.
We have these classes of distal touch, but many questions remain. Here I will discuss one: what are the constraints on distal touch? (Another, which I’ll save for another time, concerns the spatial content of distal touch). Touch can represent objects located some distance from the body, but only if those objects are connected to us in the appropriate way. I defend what I call the Connection Principle (CP): Tactual awareness of an object requires an appropriate tactual connection with the object, either directly or through some appropriate intermediary.
On my view, anything that appropriately transmits information about distal objects, and thereby allows us to have genuine tactual experiences of these objects, counts as a tangible medium. This will include various objects, tools, voluminous materials, and even organic substances such as fingernails.
What kinds of connections are appropriate? First, tactual media must transmit tangible properties, which include roughness, solidity, weight, elasticity, vibration, thermal properties, along with many others. Some tangible properties are more easily transmitted than others. These tend to be relatively sparse properties like roughness and smoothness that do not involve precise spatial resolutions. Other tangible properties, like fine texture, exact shape, contours, and part-whole relationships are more difficult to transmit, though some media exist that can transmit such information (thin gloves, for instance). Part of what makes a connection appropriate for touch then, is that tactual media must reliably transmit information about distal tangible features.
In addition, the connection seems to be closely related to exploration and control. Consider a simple case of distal thermal touch. With your eyes closed, you can experience the heat coming from a candle set before you. Even here, the exploratory actions you perform relative to the candle —- perhaps moving your palm around in front of you, feeling for the heat to increase or decrease —- seem crucial to your ability to experience the heat as coming from an external source, as located in a particular distal spot. So exploration is also important.
The same is true of distal touch involving tools. When we use a pencil or tongs to touch objects, we are able to move and manipulate the tools in different ways, allowing for coherent and stable representations of objects located away from the body. When we use such a tool, we are, in a sense, able to feel through them to the object on the other side. When we explore through touch we are able to ground and represent certain properties as located in certain places. The same is true of the use of tools for tactual projection, which occurs when the medium becomes, in a certain constrained sense, transparent.
We can say more about the constraint on exploration. Tactual media, I suggest, must mesh with our exploratory procedures (EPs). Lederman and Klatzky (1987) introduced this notion after discovering that subjects typically used a set of stereotypical exploratory movements when touching objects in an unconstrained setting. These EPs include movements like unsupported holding, pressing, and contour following that allow a subject to engage directly with objects in order to determine sets of tangible features. The use of tactual media must allow for the smooth incorporation and extension of these exploratory movements. That is, the actions we perform with tools and other tactual media must cohere with the kinds of EPs we would normally use when touching objects: we should be able to press and tap and slide tactual media across a surface, for instance. This explains why we can experience a distal surface with a pencil, but not with slack string: the string cannot transmit tangible features and we cannot perform any exploratory procedures with it.
Katz, D., & Krueger, L. E (trans). (1925). The world of touch. L. Erlbaum Associates.
Lederman, S. J., & Klatzky, R. L. (1987). Hand movements: A window into haptic object recognition. Cognitive Psychology, 19(3), 342–368.