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Re: [ontolog-forum] Looking forward at the past

To: "[ontolog-forum] " <ontolog-forum@xxxxxxxxxxxxxxxx>, "Schiffel, Jeffrey A" <jeffrey.a.schiffel@xxxxxxxxxx>
From: Pat Hayes <phayes@xxxxxxx>
Date: Mon, 6 Oct 2008 13:32:09 -0500
Message-id: <E7F0610A-6FF7-41F5-837A-75D9E62F07F9@xxxxxxx>

On Oct 6, 2008, at 12:55 PM, Schiffel, Jeffrey A wrote:

...... An
affordance, for those not familiar with the term, is a pattern of
behavior in a culture. 

Not in Gibsonian psychology. There - and I believe it was Gibson who coined the term - an affordance is a property of the perceived world which is (1) germane to the concerns of an organism, in that it provides useful information about the world, and (2) easy for the perceptual system of the organism to compute. It is the combination of salience and 'fit' to the sensory apparatus which makes affordances noteworthy. Methodologically, their importance is in providing an alternative to behaviorism's insistence on observing and theorizing only about behavior:, while being objectively definable and measurable. 

A couple of examples may help. 

Imagine that your task is to catch a ball which is flying through the air in your general direction. A useful affordance here is the apparent velocity of the ball in your visual field. If you run so as to keep that velocity close to zero, you and the ball will arrive at the same point at the same time. There is no need to solve differential equations of Newtonian physics in order to catch baseballs, in other words. 

If you look at a face, you perceive how 'mature' it seems to be. You cannot see a face without also seeing this maturity property. Faces of young children are very quickly recognized as such, and evoke different reactions in normal adults. Gibsonian psychologists have identified a very simple affordance for this, which is the degree to which a vertical-perspective distortion of a 'normal' face fits the face being observed, using the eye-line as center. Young kids have top-large heads, and the ratio changes through puberty, becoming fully 'adult' around age 25.
This can be computed very rapidly and reliably from close-to-raw visual data (a few synapses from the human foveal cells, or in a digital camera chip) and corresponds to human age judgements very closely. 

As you can see, these have to do with perception, and they have nothing at all to do with culture or behavior. This is typical: Gibson was primarily a perceptual psychologist, after all. 

Pat Hayes
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