Misperceiving the affordances in anorexia nervosa

Alice had a few problems with doors too

It's always hard to evaluate the impact of your research, although funding bodies are increasingly asking that we do so. I always struggle a bit, because the connection between studying, say, the perception of affordances and impact on policy or clinical practice is rarely a straight forward story. My problem is that I think that, if you ask a question the right way the answer will always come in handy to someone at some point, and that this is a big part of how science has its impact. 

Case in point: in 1987 Bill Warren was investigating the perception of affordances for passing through an aperture, such as a door. Apertures can vary in width, but the question facing the observer isn't 'how wide is it?' but 'can I fit through it?'. Bill was describing affordances using pi numbers, ratios of widths in the world divided by widths of some relevant body scale. An aperture wider than your shoulders, say, would yield a ratio larger than 1. For a given person's shoulder width, different apertures would produce different ratios. Across people, apertures of different sizes will produce the same ratio as shoulder width changes. It's a way of factoring out the effect of the size of the observer, and it's based on the idea that we percieve the world in terms of our own ability to act on it.