Affordances are not probabilistic functions

The journal Ecological Psychology is hosting a special issue with papers from a Festschrift for Herb Pick. Karen Adolph and John Franchak have a paper that caught my eye about treating affordances as probabilistic functions, effectively applying standard psychophysical techniques to the study of affordance perception. 

The idea is this: affordance research typically treats affordances as all-or-none, categorical properties. You can either reach that object or you can't; you can either pass through that aperture without turning or you can't. You then measure a bunch of people doing the task as you alter some key parameter (e.g. the distance to the target, or the width of the aperture) and find the critical point, the value of some body-scaled measurement of the parameter where behaviour switches from success to failure. For instance, you might express the aperture width in terms of the shoulder width and look for the common value of this ratio where people switch their behaviour from turning to not turning.

There's No Prospective Information About Friction, or, Why I Fell Over on the Ice

In which I justify why I, a healthy perceiver-actor, slipped and fell on a clearly visible icy patch, breaking my wrist for the second time, using SCIENCE.

It's been a cold, icy winter here this year, and 6 weeks ago I slipped on a patch of ice and fell entirely on my (previously broken) wrist. The ensuing physics did enough damage that I needed surgery to set the wrist with two pins, and I am only today out of the cast. These kinds of falls and injuries are very common; half of all falls  in the US are caused by insufficient friction, and the types of injuries (broken wrists and collarbones, etc) suggest reactive responses to the slip - people using their arms to try and regain a sudden, unexpected loss of balance. 

The two papers I'm going to talk about are from the lab of my favourite developmental psychologist, Karen Adolph, who has done some excellent affordance work using the transition from crawling to walking as a way to studying the changing perception-action performance of children. This research, however, asked about whether a perceiver can detect information about upcoming friction conditions and use this information for prospective control. The answer seems to be no, because there isn't any information. Given that action requires information, the absence of information might explain the often catastrophic failures of action we see on ice and other low-friction surfaces.

At least, that will be my story.