My proximate motivation for starting this blog is that I have become an active commenter on a couple of blogs, and I both envy the authors and feel bad when I want to post a reply elaborate enough that it might look like thread hijacking. With that in mind, I want to rift for a bit off of Charles Wolverton's reply to my comments on Sabrina Golonka's post over at Notes from Two Scientific Psychologists. I was trying to cut the difference between Ecological and traditional Behaviorist ways of thinking, and Charles said:
In the absence of the tone, the lever doesn't necessarily invite purposeful action, ie, doesn't offer an affordance. But as Eric notes, the rat has learned to associate the tone with a purpose - getting access to something offering "ingestible" - so that the tone's sounding results in the lever's otherwise purposeless offer of "graspable" becoming purposeful, and hence an affordance.
This made me feel great, but also a little squeamish. It is great, because Charles clearly got my point, and phrased it better than I did. It made me squeamish because of the very last word: affordance.
The term 'affordance' was introduced by Gibson, and has since been adopted by many others and adapted for many purposes. One challenging topic as I work on the incipient Ecological Psychology textbook is what to do about how broadly or how narrowly to use the term affordance. My initial inclination is to use a very restrictive reading of the term. The most natural use of the term 'affordance' is to refer to a behavioral action made possible by a matching between the crude physical features of an organism and the nuances of the immediate environment. My hand is the rough size and shape that allows the picking up of a coffee cup, my frame allows me to fit through standard doorways, etc. The affordance is thus the relationship between me and the objects in question. The further we get from such straightforward relationships, the more nervous I am about using the term 'affordance'.
One reason I am nervous, is because of how we (ecological psychologists) want 'affordance' to relate to the other key terms in our system 'invariants', 'specificity', and 'perceptual systems'. We are particularly interested in affordances that can be perceived, that is, affordances that structure ambient energy (e.g. light) in a manner that specifies the relevant physical properties of the object. When such specification is present, a properly attuned perceptual system can accurately detect the properties of the world. This is important, because it provides a definition for perception, which allows us to distinguish the perceptual process from other (potential) psychological processes. When we are attuned to the proper higher-order invariants, the affordances themselves become our 'percepts', they are given directly in perception.
So, back to the rat and the lever. It is very easy, with the most natural use of the term 'affordance' to talk about the rat perceiving the lever as affording pressing. The physical structure of the rat and the physical structure of the lever take care of that perfectly fine, and everything about the lever being press-able by a rat-like organism is specified in the ambient light (or so I assert for the purpose of this example). However, I'm nervous saying that the affordance of the lever changes when the tone sounds. Yes, the rat normally lives in a world where pressing the lever is boring, but when the tone sounds the rat suddenly finds itself in a world where pressing the lever produces food. Yes, because the rat has jumped between those two worlds many times before, the rat is now so built that it presses the lever many times when the tone sounds, but rarely otherwise. Yes, one can objectively describe the rat's behavior towards the lever as food-directed when the tone is sounding, but no such description is appropriate the rest of the time. I'm a crazy behaviorist, I'm happy with all that. But I'm nervous saying that the 'affordance' of the lever has changed. The physical relationship between the rat and the lever has stayed the same, and the lever affords pressing equally in both worlds.
Am I being too picky?