Reading Group - Gibson (1979) Chapter 6 Part 1

Chapter 6: Events and the information for perceiving events

Thus far, Gibson has been talking about how we perceive objects. But, things in the world often move around, so we'd better be able to perceive things that are extended in time as well. First off, Gibson describes the properties of surfaces that are relevant to events. He then identifies a number of things that can happen to surfaces during events. The nature of these changes will determine what types of optical information might specify particular events (this will be discussed in Chapter 6 Part 2).

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.

How to Build a Valid Measure of Behaviour

One of the main problems facing psychology as a science is the issue of validity - what is the relationship between what you measured and what you are actually interested in? One of the things I like about studying movement is how straight-forward this issue is - we're interested in the control of action, so I just measure the action! The most common directly measured kinematic variable is displacement, or position over time; you can then derive (via differentiation) the various rates of change of the previous variable (velocity, acceleration, jerk, and, I kid you not, snap, crackle, and pop). In human movement we never tend to go past jerk, and you can do pretty well with just position and it's rate of change, velocity.

This post will discuss how we start from these basic kinematics and derive a measure of coordination that is  entirely valid, covers the entire space of possible states and provides a unique number for every possible state within that space. Psychology doesn't have a lot of these kinds of variables, but you need to be able to characterise your state space to do the kind of modelling I've been describing and advocating.

Stuff on the Internet (3 December 2010)

Some things that have come our way recently that are somewhat on topic for the blog.

Science

Ed Yong has a (paywalled) piece in the New Scientist about how birds visually perceive magnetic fields. He followed up on Not Exactly Rocket Science with interviews with two scientists working on this fascinating question: Klaus Schulten and Thorsten Ritz. 

NPR covers an interesting study on the fact that blindfolded humans tend to walk in circles. This fairly robust result is not due to handedness or any obvious biomechanical asymmetry, but seems to be the result of sensorimotor drift accumulating in the system (link to paper). Without calibration by vision, our sense of direction becomes increasingly noisy. This relates nicely to some data from a study some colleagues and I really need to write up, in which we got people to misperceive which finger was receiving vibrations after an extended period without vision of the hands.

The biomechanics of pterodactyl flight. 

Baroness Greenfield continues her war on the neurological consequences of modern technology.

Cool toys...er, I mean, educational stuff

Microsoft's Kinect motion tracker uses structured infra-red light arrays to passively track multiple moving objects. Deformations in the field are robust enough to detect game-specific motions as well as faces, etc. There's apparently a lot of people using the IR fields in their art (e.g here, via BoingBoing; mildly NSFW depending on where you work) and I think these could be a fun way to teach optic arrays to students. All I need is a Kinect and an IR sensitive camera...dear Microsoft...

Hi-speed video taken from a train.

Media

I caught up on some Rationally Speaking podcasts while recuperating from surgery on my wrist; these are the ones that caught my eye:

• Experimental Philosophy - to be honest, I have yet to hear an argument why this isn't just psychology done by people who don't really know how to do psychology properly.
• Thought Experiments - they worry about basically the same things I do, but are more generally optimistic about their utility.
• Evolutionary Psychology - here they were a little less generous, which I think Sabrina would be ok with.

Newton TV: I haven't had a chance to really poke around, but what could be wrong with science videos hosted by scientists?

Blogging
There's a new blog  on being a science blogger called The Science of Blogging. We're looking forward to some good advice for broadening our reach a bit.

This editorial about the dangers of science blogging is almost entirely wrong.

What Does Coordinated Rhythmic Movement Have To Do With Anything?

In which I provide an answer to a question I get asked by everyone, including grant reviewers, students and random people who make the mistake of asking what I do for a living.

I've spent numerous recent posts talking about coordinated rhythmic movement. This is my bread-and-butter experimental task, my go-to example for studying all aspects of perception, action and learning. I'm branching out, now I have my own faculty position, but coordination is where it's at. 

The single most common question I get is "why study this? Surely it's just some fake movement task; I mean finger-wiggling, who ever even does that?" I wouldn't mind so much, but I even get this question from grant reviewers, scientists who should know the answer. Doing science properly is important, but communicating that my methods achieve this matters too, not least because today's funding climate demands it.

So, coordinated rhythmic movement: what the hell?

Life and Other Vague Categories

Awhile back I proposed that the distinction between what is cognitive and what is non-cognitive is problematic because of the types of categories we're dealing with - namely, vague artefact categories rather than clearly bounded natural kinds. I suggested that this causes important problems for the study of cognition itself (because we have no principled method for deciding what counts as cognitive) and for philosophical arguments related to cognition (e.g., the coupling-constitution fallacy) because these also depend on having some idea of what counts as cognitive.

Brief Note: Daryl Bem and Precognition

In case you missed it, the Journal of Personality and Social Psychology, a flagship APA journal, published a study by Daryl Bem containing evidence for psi (precognition). I didn't really want to post in too much detail about this study (which has been doing the rounds online all week) because I'm not that interested in being a science journalist. But I did feel it was worth posting a few links and some brief comments to this provocative paper, because it raises a lot of interesting questions about the business of doing psychological science.Should a paper on precognition be published in a major social psychology journal? How did Bem get his results? How seriously should we take what seems to be evidence for something that a lot of other science suggests is impossible?