Lecture 25: The Mechanical Basis for "Getting About Among Things" (Turvey, 2019, Lectures on Perception)

This chapter is about the mechanical consequences of interacting with the environment; what happens when we come into physical contact with things. Importantly, though, we are going to focus on the informational consequences - what information is created by mechanical interactions, what does it enable us to perceive, and what is the medium for this information? Broadly then, the topic of this literature is dynamic/effortful touching. 

Talking about this topic will enable us to make a few key points. First, dynamic touch is a commonplace activity, namely the kind of activity an ecological psychology takes as it's main topics. Second, it engages with the ecological hypothesis that information is specific to the dynamics of what it is about, and not specific to the medium in which it lives. Visual information and haptic information, for example, are the same kind of thing, and are sometimes even the same information variable. The important thing for a theory of perception is the information, and not the details of the medium, nor the anatomy that happens to pick it up. 

Turvey then spends most of the chapter reviewing key empirical findings from the ecologically motivated investigation of dynamic touch. The key perceptual variables are not things like mass or weight, for example, but the moments of inertia; how an object resists changing state. This leads to tasks that involve hefting or wielding (changing the state, essentially), and experimental manipulations that separate out things like mass from mass distribution and the inertia tensor. 

Several things emerge. People can perceptually identify different properties via similar movements, by attending to different properties of the object. This demonstrates that intentionality matters (you can ask people to judge different things and that drives attention to different variables), and that in any task there are multiple variables available, defined across various scales and relations between properties (the task is multi-fractal). These mechanical properties are also the basis of perceiving things about ourselves, as well as what objects we are mechanically interacting with; we perceives things about our limbs this way as well as things our limbs are dynamically touching. There's no in-kind difference between perceiving ourselves and other things, it's all grounded in informationL. Finally he notes the case of weight perception, and how it is not based on the weight of objects, but on their inertia (this connects to Gibson's point, that the variables of perception must be empirically discovered and confirmed, not assumed from one description of the task at hand). This connects to things like the size-weight illusion and reveal it's only an illusion given the assumption of the wrong variables at play. 

Turvey then discusses a fascinating case, a man called Ian Waterman who lost all proprioception and had to effortfully replace that perception of the environment with vision. The details of his ability to do so and the limits on what he could do are a fascinating story for ecological psychologists (some clips from a documentary here, and there's a great book about it too). 

Turvey briefly reviews his hypothesis that the medium for all this mechanical interaction perception is the body considered as a tensegrity structure (Turvey & Fonseca, 2014). The hypothesis is that the way the body deforms under mechanical pressure provides a medium for the same kinds of structure as the optic array does; it has the right kind of features to support implementing informationL. Analogous to the optic array, the key is the right level of description - the optic array begins with optical solid angles, for example, rather than points or rays of light. 

Turvey then notes briefly that hearing is also about the detection of mechanical events, just not necessarily ones in which our body was involved. He points to the work of Gaver (1993a, b) on the kinds of events that can be specified in the acoustic array, and how we can 'hear what a struck object looks like' because of the nature of the informationL involved.