Notes on J.J. Gibson Part I [posted 3/11/00]


Notes and thoughts on J.J. Gibson's Ecological Approach to Visual Perception. Part I

Reasons for reading.

        This may seem like an odd book to start out on - given the tentitive topic of the line of inquiry I'm following. But it made sense to me for several reasons. First of all, I had it in hand, and the circumstances of my getting it were rather intresting. Second, It seems to be pretty heavily cited, its one of those "a classic in its field books" But most importantly, I'm very intrested in some of his ideas and his theoretical methodology.

        Gibson is usually credited with coining the term "affordence" and is sort of the founder of the ideas of "Ecological Perception". (My impression is that Ecological Perception of the fifties and sixtes is to current "mind-body studies" almost as Cybernetics and the Systems Theory of that era are to modern Dynamical Systems and Complexity. Interesting restatements, or perhaps reteration with verification...)

        The basic argument of the book (at least so far as I have read) is that it is a mistake to consider the problems of visual perception (and the implication is for other senses as well) from a static abstract perspective. Gibson argues that the classical deliniation of the problem of extracting information from and classifying the visual world is essential misconcieved. For him the individual is not some sort of stationary camera-obscura making logical models of the world in an abstract cartesion space. His conception is intrequeing because it is far more dynamic. He sees the individual as almost a moving sampleing point in a very concrete "visual array", detecting the "invariant structre" of the environmental layout in relation to its (the enviroment's) possiblites for action and perception.

        The book has an almost philosophical tone. It is almost as if he is carefully pulling together the elemnts of a new worldview. Perhaps the long listings and categorisations are necessary due to the simultateious radical changes and subtle difference from more traditional ideas about perception, but I found his God-like enumerations a little off-putting. He is presenting a perspective which to him is entirly self consistant - I'm usualy more convinced when there are some exciting holes...

        He spends the first couple of chapters devloping what is essentialy an ecological geometry system. That is, as system for describing and classifying the world which is concerned soley with its behavior <I>as directly perceived by the observer<I> rather than one which is rigorously accurate to an abstract mathematical idealism. He works hard to make a distinction between the actual physics of what is going on the way the environment is actualy experinced. I never got the impression that he was in any way trying to question the valitiy of a physical explanation for phenomena, but he was very definitly questioning the appropriatness of using the same terms and concepts to describe the world as it appears. A good example is on p.54 where he states that from a physical perspetive, we can only see light (it is the only thing actually entering our eyes), but as far a pserception is concered, light is a thing which cannot be seen. (only illuminated objects)

        Again, the philosophical flavor of the book comes through. It is evident that he has spent a great deal of time trying to understand the world from a fairly innovative perspetive - to see it how it actually looks, not just how we've all been taught to see (or think about how we see). It is less that is arguing that the facts which have been discoverd about perception are wrong (allthough he does make specific claims..) and more that the wrong conclusions have been drawn - the facts have been misinterprated.


-Interesting statement on p.63. He makes the claim that there is no actual information in the light (or more specificaly, in the stimulation of the retina). I'd guess that he is implying that the information lies in the configuration of the visual system/motor system to the light? Hard to tell because the example he uses is an illuminated fog - in which there is very little information of the more tradditonal sense either.

p.57 "...stimulus information is not lost from the environment when it is gained by the observer. There is no such thing as conservation of information."

p.68 I liked how he distinguished between location by metric and location by the relation of inclusion. It does seem to map better to how we actually work with the world: "the broken window is in the wall of the house over there." rather than "the broken window is 60 inches from the south-west edge of the wall of a house which is 200 yards to your right" adimitedly my two examples are contrived and show very different levels of precision, but I think that is part of the point. Gibson is not arguing that we cannot describe the world using high-level abstract concepts. He is saying that the unconscious or "natural" level of perception, we do not use such concepts - and that what goes on in not just less precise, it may be qualitatively different.

p.83 Gibson is making the assertion that object perception is not fundamentally based on detection of outline or sillouette with 3D form added by processing shading and other visual cues. He seems to argue that 3D forms are perceived almost directly by detecting the transformations andd relations of shapes as the object or the observer moves. Certainly both methods sound feasible (perhaps both are used). It would be interesting to somehow devise and experment to see i a prson culearn to see if only preseneted with still images, or images which were somehow decoupled from the movements of the viewr. Another kitten thing...

        This may also explain why a 2D shaded " cube " can be made to pop in and out. The illusion doesn't work in 3D because moving the head caused the shapes to transform in an unambiguous way.

        I'm also reminded of the optical illusion of the room which is designed so that you look through a peephole and the people inside seem to have radically different sizes. My understanding of the conventional explanation is that the viewer is deprived of binocular depth cues and forced to rely on the intentionally misleading perspective cues. But Gibson might argue that the most important component of the illusion is that the viewer is forced to observe from a fixed vantage point and is deprived of movement cues.

        I imagine he'll probably get to it, but Gibson's emphasis on the textures in the optic array might explain why the illusion of TV works. - we don't care that the parallax cues are missing because the optical texture and occlusions function the way we expect them to.

pg. 114 Gibson mentions that there are two fields of view - one for each eye. This fact works well with his conception of an environment of potential points of observation. In a sense he can shift the emphasis from the triangulation ability of binocular vision to a consideration of the benefits of always being able to see the world from two places at the same time. When the ability to make small movements of the head is added...

        --be interesting to analyse videotapes of people who have been given confusing perceptual tasks. Do they wiggle their heads around? Lean forward? Reach out to touch the object in question?

pg. 122 Many of these statements about perception seem especially descriptive of the experience of being drunk or otherwise perceptually out-of-whack. Perhaps because the "higher cognitive abilities" are discombobulated? We have less ability to construct analytic models so we rely more on perception itself?

pg. 129 "An affordance points both ways, to the environment and to the observer."

pg. 135 Some discussion of social affordances.


Not sure where I'm going here, but affordance has a relational quality which might make it a useful concept to base a culture theory on. Something about the way afordances create a mapping from object to action, a sort of shadowing of potentials which are simultaneously based in the perceiver and rooted to the physical reality. ]

pg. 138 Gibson seems to be making some distinctions between his affordance theory and more traditional gestalt theory. Arguing that affordances are invariant and always perceived, just not always paid attention too. This seems if fits well with a frame perspective, maybe I'm missing something.

pg. 140 " is because the affordances of things are specified directly in the stimulus information."

        I guess he's saying that rather than perceiving a wire-frame outline, shading it with color, and then attempting to tag and categorize an object, what we perceive are the potential uses of the object which we then assemble into a category. I guess I'm not entirely clear how he posits the leap from the visual array to direct perception of affordances. It seems like a big leap. But perhaps by applying a similar methodology to describe a "sensory array" or sensorium...

pg. 143 "When Koffka asserted that 'each thing says what it is', he failed to mention that it may lie."


-the dump experiment:

        Watching/recording people as they deal with and try to figure out an unfamiliar object. If the task is being done by a brainstorming group, what would they say to each other? What do people say when asked to describe the process?

-affordance matching/Milgram's letterbox

        What paths/actions do people take when they find a letter and a mailbox in the same "frame"? How do the addresses on the letter change what happens?

- Questions about the nature of variance/invariance as meant by Gibson, and when expanded to deal with affordance of humans and symbols.

        one "lead" for getting at the meaning of invariance might be Gibson's idea of the Principal of Reversibility (i.e. you can always turn your head back) It seems like this is tied to an idea of expectation/reproducibility: Invariant objects behave as expected?

        Perhaps there is a link between Gibson's Invariance and the Shannon concept of information?

Shannon Information Measure roughly:

        the information in a signal is equal to the decrease in uncertainty about which state a system is in









Commentary: -none-

So far, nobody has had anything to say about this text. If you would like to comment, please email skye.