Monday, September 20, 2010

Runeson and Affordances

Here is how Runeson describes the information one uses in static viewing of the Ames room in order to perceive a rectangular room.
Geometrically, the chances that an equivalent configuration would occur by random is therefore only in a 100 million and that is for a very simple, barren case. For a room without the size restriction or with furniture and structured surfaces, the chances are many orders of magnitude smaller yet.
Physical constraints. Solid chunks of matter can not be distributed arbitrarily in space, especially not in a gravitational field. Hence, out of the total set of geometrically possible configurations, only a subset can be physically realized (Todd, 1985). The subset that can be realized through more or less natural shaping processes is even smaller. The physical constraints that apply to the manufacture of roomlike enclosures include gravity and other load forces, strength and weight of materials, methods for shaping and joining parts, economy of space, materials, and labor. One must then ask, do prevailing physical and ecological constraints suffice to exclude the kind of room shapes that would be projectively equivalent with normal rooms?  (Runeson, 1988, p. 299).
Part of why I like this is that it seems to me to be talking about the good old-fashion geometry and physics I learned in college and before.  I get that.

But, it also makes me wonder how one fits the talk of affordances and the ecologically meaningful into the story.  Affordances and ecological meaning here seems to me to be superfluous.  So, I don't really see how Runeson needs the kind of thing that Gary describes in comments on this earlier post:
I think the best way to get a grip on ecological information is to forget about the complexities of higher mammalian perception and look at the bacterium as the exemplar of detecting ecological information.

If you put a bacterium in a sucrose solution, the bacterium is able to detect or discriminate the differential sucrose gradients and orient itself such that its propulsion will maximize the exposure to sucrose. For ecological psychology, *this* is the paradigm case of successful perception. The ecological information in this example is the nutritional properties of the sucrose. There is nothing intrinsic to the sucrose molecule that makes it "ecological information" or "nutrition". Rather, it is ecological information only in relation to the nature of the bacterium's specific metabolism. But this doesn't make it "subjective".


  1. The answer to your question is in Runeson:

    What is equally important, as explained above, is to avoid using overly rich descriptors for the to-be-perceived environment. Also in this respect, Gibson has initiated a revised view by rejecting the uncritical use of the euclidean space conception and introducing new descriptive notions such as surface layout and affordances (e.g., Fowler & Turvey, 1982; Gibson, 1979, part 1). The present analysis provides a clear case in support of the Gibsonian assertion that in order to avoid pseudoproblems, theories of perception will necessarily have to rely on an organism-relevant theory of the environment (Mace, 1977). [Runeson, pp301]

    “Affordances and ecological meaning”, i.e. things taken from an organism-relevant perspective, are the types of ecological constraints that act to constrain the space of things-needing-to-be-specified. Organisms don’t need access to the Euclidean description of the world, they need access to the ecological description of the world – affordances.

  2. "Gibson has initiated a revised view by rejecting the uncritical use of the euclidean space conception and introducing new descriptive notions such as surface layout and affordances"

    But, here is what is tripping me up. Runeson does not seem to me to be using surface layout, etc. He seems to me to be using physics and indeed Euclidean geometry. The discussion of "The variability of six-panel enclosures" seems to be an exercise in basic features of Euclidean geometry.

    What I am having trouble with is the theory apparently failing to mesh with practice.

  3. Gibson did more than just reject the uncritical use of "the euclidean space conception". He rejected "the euclidean space conception", but Runeson uses it.

  4. Here seems to me an outright rejection of geometrical space, not a mere rejection of an *uncritical* use of euclidean or geometrical space:

    "I am asking the reader to suppose that the concept of space has nothing to do with perception. Geometrical space is a pure abstraction." (Gibson, 1979, p. 3).

  5. In science, you're allowed to rely on abstractions. Physics does this all the time, with it's mathematical characterisation of (e.g.) space-time. All science does this; but psychology is uniquely vulnerable to what James called 'the psychologist's fallacy', which is when you take your abstract description and make it the mechanism. Gibson is trying to restore geometry to it's rightful place: an excellent set of tools for conceptualising things but not the thing itself.

    So he is indeed rejecting the 'uncritical' use. Also, Euclid only gets you so far: there are many geometries and it's an empirical question as to which is the most useful tool.