We are nearing the end of the Foundational Concepts section of the book, and we have arrived at one final historical attempts to explain perception; the Gestalt school. This chapter doesn't actually spend any time on Gestalt, however, but instead lays out the things Gestalt was developed to oppose. Those things are atomism, anatomism, and mechanical order.
The basic question for psychologists is to explain the order in behaviour; why do people do things the way they do, rather than another way? Everything that is a Cartesian programme (so, everything so far) assumes that people are mechanisms, specifically machines. Machines are built of parts (atoms, in a generic sense; smaller parts that contribute something specific to the overall behaviour of the mechanism) and these are arranged in specific ways so that the parts can work together correctly (the anatomy, in generic terms). A clock has 'atoms' (smaller components like wheels, cogs, hands, etc), and 'anatomy' (these components must be assembled in a particular way to function as a clock) and the result is a mechanism who's behaviour (the order) is a function of the atoms and anatomy.
In perception, we have Helmholtzian ideas such as the specific nerve doctrine, etc, and around his time (late 19th century) develops in histology revealed the structured anatomy of the nervous system. Helmholtz's ideas were an application of the Cartesian programme to perception and mind, and they seemed to all have anatomical support. The order in, say, perception, seems to arise from the order in the anatomy of the nervous system. Neurons implement the elements, and connections between neurons implement the association required to link these elements into mind.
The rest of the chapter describes the notion of mechanism, and the limitations of this notion.
A machine is something that is made up of smaller parts. Each of these parts serves a function (defined by it's structure), and their functions add up to the function of the machine they are a part of. Given all this, you can study a machine via decomposition (breaking it into parts and studying the parts separately). This allows for reductionism as a research strategy. Another implication is that machines cannot show impredicativity (Lecture 3) - this is considered a good thing, because impredicativity is to be avoided in this framework, but obviously this is going to be a problem in developing an ecological approach.
The Cartesian hypothesis is that everything is a machine; both animate and inanimate things are machines, just of varying complexity. To explain the behaviour of something, you must propose a machine-like account; a mechanism. This mechanism allows you to simulate the behaviour of the system. Some scientists (e.g. Lord Kelvin) effectively equated 'machine' and 'simulator'; having the mechanism that let you simulate meant you understood the machine. Others (e.g. Arthur Eddington) thought that not everything could be modelled in this strictly syntactic way.
One of the assumptions of the machine metaphor is that every machine behaviour can be explained using forces acting on unalterable objects via local causation. Turvey spends a lot of time then discussing examples of scientists trying to develop machine like explanations for a variety of physical phenomena and failing. One example is the caloric theory of heat; that heating entailed the addition of caloric atoms that had the properties required to create the effects of heating such as melting. Another was the theory that electricity was carried by two forms of 'subtle fluid'. The issue here is that first, all these explanations rested on additional hypothesised elements such as the ether to work, and so got very complicated, and then second, all these theories were replaced with less machine-like explanations. The 'mechanical programme' from Descartes didn't last, in physics. The implication is that it shouldn't be allowed to last in psychology, either.
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