Monday 9 November 2020

Turvey, Lectures on Perception: The Story So Far

I have now reviewed the first 7 Lectures on Perception from Turvey' textbook (posts indexed here). I feel like I've reached a natural pause point before carrying on with the rest of the lectures, and I wanted to summarise what I thought has been going on so far.

These are lectures on perception, quite generally. While Turvey will explain the ecological approach, that's not what is currently going on. Right now Turvey is laying out the scope of the question 'what kind of material system could be a perceiving system?' and reviewing the typical, non-ecological answers to that question.

The main takeaway at this point is that we have been trying to answer that question using 17th century notions of material systems, specifically Newtonian mechanics. This has placed what turn out to be unacceptable restrictions on the kinds of properties we are allowed to invoke, and theories of perception have had to fill the gaps with unpayable 'loans of intelligence'. 21st century physics, however, has more on offer; complexity science and quantum mechanics teach us many valuable lessons on how to expand our horizons so that perception becomes possible, rather than miraculous. 

In Lecture 1, he establishes that a perceiving system must be understood as epistemic, intentional, and as a system. Systems are collections of parts that depend in some way on each other for how they function. Intentional systems are about something, and epistemic systems know about something. This lays out the question for a science of perception: what kind of material system can come to know about things?

To answer this, we need to think about what sort of properties material systems are allowed to have. Turvey introduces Newtonian mechanics as the science of physics we tend work within, and the Cartesian property dualism that comes out doing that. These are sets of assumptions about what the legitimate elements of a science of perception has to work with, and they lead to the mess that is perception as indirect, specifically a three term relation;

  • The Newtonian notion of local causation implies a linear chain of events, one thing causing the other over time. For perception, this implies some kind of copy/simulation of the world being carried by (for example) light and projected to an observer, which causes perceptual experience (Lecture 4).
  • All efforts to identify the nature of the simulation and therefore what is projected leads to an assumption of poverty of stimulus
  • Given this, there must be at least one thing standing between the world and perceptual experience of the world; perception is indirect, involving the world, the perceiver, and at least one intermediate entity
  • These always and inevitably require unpayable 'loans of intelligence' to make work
  • Even empiricists trying to avoid the problem fall foul of it, because they remained committed to Newtonian mechanics and local causation
Throughout these Lectures, Turvey spends a lot of time illustrating that physics has come a long way since Newton, and that the legitimate set of physical properties a perceptual system might be built from is much wider and more interesting. Specifically, quantum physics has revealed one domain in which properties can be impredicative, that is, defined with respect to the system in which they are currently playing a part. These properties can then take part in non-local causation. Turvey proposes that if we can develop an ecological scale physics that can include impredicative properties and therefore non-local causation, we enable the possibility of perception as direct, specifically a two term relation (world and observer). 

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