Friday, September 17, 2010

Gibson and Turvey/Carello versus Runeson on Physics and Perception

In The Ecological Approach, Gibson is keen to move away from the concepts and quantities of physics, and perhaps geometry, as useful theoretical apparatus for vision science.  So, for example, in the summary for Chapter 1, he writes,

The environment of animals and men is what they perceive. The environment is not the same as the physical world, if one means by that the world described by physics.
     The observer and his environment are complementary. So are the set of observers and their common environment.
     The components and events of the environment fall into natural units. These units are nested. They should not be confused with the metric units of space and time.
     The environment persists in some respects and changes in other respects. The most radical change is going out of existence or coming into existence.
Turvey & Carello, 1986, say similar sorts of things:
Fig. 1.1. In conventional discussions of space perception, 'space' is a mathematical concept. Theory and experiments focus on how an observer perceives points, distances between points and motions of points localized by triplets of values in a Cartesian coordinate system. The mathematical conception of space is traditional and, perhaps, convenient but it has little bearing on what animals (including humans) need to perceive in order to get around successfully in their cluttered environment. (Turvey & Carello, 1986, p. 133).
Runeson, for his part, however, does not seem to abide by this prohibition on the concepts and quantities of physics and geometry.  For example, he writes,
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).
Personally, I like Runeson's approach, because it is more familiar to me.

Turvey, M., & Carello, C. (1986). The ecological approach to perceiving-acting: A pictorial essay. Acta Psychologica, 63(2), 133-155.


  1. I don't think Runeson is really departing from Gibson in talking about the geometrical layout of rooms as they exist apart from animals. In denying the relevance of geometric space for vision, Gibson was simply emphasizing how the "given" for animals is never a completely static geometric snapshot that exists in an instantaneous slice of time. The information in the environment animals seek out is extended over time. Since normal animals are mobile, if you set up the problem of vision in terms of a static geometric array of light rays, you will miss the way in which transformations of patterns across the retina are just as stimulating as a static geometric pattern. By denying that geometric space is relevant for animals, Gibson is claiming that animals *directly* perceive motion rather than deduce it secondarily from change of position.

    Moreover, in distinguishing between the world of physics and the ecological world, Gibson is trying to emphasize how animals are not interested in photons or pure wavelengths. The bee is not attracted to a particular wavelength, but rather, to an opportunity for action which is specified by the invariant patterns that result from stimulus transformation. Here's another example: a animal who is escaping from predators is not interested in the geometric or physical profile of a burrow, but rather, the way in which the hole affords safety. Sure, you could talk about how the geometric profile of the hole reflects the photons and how these photons impact the retina which are then transduced into electrical activity. But Gibson claims these are physiological or anatomical facts, not psychological facts. For psychology, the relevant facts are the way in which the hole affords an opportunity for escape and shelter. Or at least that is the claim.

  2. I'll try and reply in more detail later; I've broken my wrist so typing is a pain.

    There's no 'prohibition on the concepts and quantities of physics and geometry' in ecological psychology; there's just the understanding that those concepts are not special or privileged. Just because physics treats 'space' the way it does doesn't make that the 'objective' yardstick against which to evaluate or conceptualise biological perception. Think affordances; these are physical, real properties of the world expressed with respect to properties of the organism.

    This push isn't anti-physics, it's simply anti-reduction-to-physics.

  3. Runeson isn't arguing that we organise our behaviour with respect to the variables that are typically used to describe physical layouts (e.g., metres), and this is what Gibson was actually concerned about. Runeson is simply commenting on the likelihood (given natural physical constraints) of enclosed spaces possessing certain layouts. This isn't really a departure from the other quotations.

  4. I probably should have added a page number to the quote from Gibson, although all of you may know it. But, it is (of course), the summary for Chapter 1.

    Now, regarding Gary's suggestion that Gibson is concerned with rejecting snapshot vision in favor of vision over time (or dynamic vision), I'm thinking that this is not what Gibson is up to as this early stage. I agree that this static versus dynamic matters for Gibson, but that is not what he is up to at that point in the book.

    By contrast, I think Gary is right that part of what Gibson seems to be up to early on is to indicate that perceivers are not interested in, or do not perceive, geometrical configurations or physical properties.

    There is, however, a residual additional concern, it seems to me, in Gibson's claims that "The mutuality of animal and environment is not implied by physics and the physic sciences. The basic concepts of space, time, matter, and energy do not lead naturally to the organism-environment concept or to the concept of a species and its habitat. Instead, they seem to lead to the idea of an animal as an extremely complex object in the physical world. The animal is thought of as a highly organized part of the physic world but still a part and still an object. This way of thinking neglects the fact that the animal-object is surrounded in a special way, that an environment is ambient for living object in a different way from the way that a set of objects is ambient for physical object. The term physical environment is, therefore, apt to get us mixed up and it will usually be avoided in this book.

    Every animal is, in some degree at least, a perceiver and a behaver. It is sentient and animate, to use old-fashioned terms. It is a perceiver of the environment and a behaver in the environment. But this is not to say that it perceives the world of physics and behaves in the space and time of physics. "

    Chapter 2 also starts,
    "According to classical physics, the universe consists of bodies in space. We are tempted to assume, therefore, that we live in a physical world consisting of bodies in space and that we we perceive consists of objects in space. But this is very dubious".

    It is the residual that seems to me to be a radical element in Gibson's discussion, one that Gary, Andrew, and Sabethg seem not to address. These sounds like encouragements to "purge" physics from vision science. They sound like the things that Runeson has not done (to his credit, I think).

  5. Andrew, sorry to hear about your injury. I had worried that your silence had meant that I had offended you. Best of luck on the mend.

  6. I'm not that easily offended, although I apparently afford breaking to a soccer ball. :)