Are Illusions Even a Thing?

Traditional vision science is very excited about illusions. These are cases when perception seems to break down; there is a mismatch between what is out there and what we experience, and traditional approaches consider these breakdowns as clues to how vision has to work, given what it is working with. 

Ecological psychologists don’t like illusions. Typically, they occur when information is either made ambiguous or faked, and in general we think these are the wrong situations to study perception in. We sometimes engage with the literature on these effects, but usually to show how the trick is the result of not thinking ecologically. 

Rogers (2022) has taken this basic analysis but gone one interesting step further. He’s argued that the notion of ‘visual illusion’ is simply not a clear category; it’s not a useful way to describe any of the effects people study. He argues that there simply is no sufficient definition of what an illusion is that works, and that what we call illusions are just either tricks (as above) or inevitable consequences of how the visual system works. 

I am broadly on board with this additional step, and it’s made me think hard about what illusions are and how best to respond when people use them against direct perception. 

Brains Don't Have to be Computers (A Purple Peril)

A common response to the claim that we are not information processors is that this simply cannot be true, because it is self-evidently the case that brains are transforming and processing information - they are performing computations. Greg Hickok throws this ball a lot, and his idea is clear in this quote from his book 'The Myth of Mirror Neurons':

Once you start looking inside the brain you can’t escape the fact that it processes information. You don’t even have to look beyond a single neuron. A neuron receives input signals from thousands of other neurons, some excitatory, some inhibitory, some more vigorous than others. The output of the neuron is not a copy of its inputs. Instead its output reflects a weighted integration of its inputs. It is performing a transformation of the neural signals it receives. Neurons compute. This is information processing and it is happening in every single neuron and in every neural process whether sensory, motor, or “cognitive.”

Hickok, pg 256.

There are two claims here. First, neurons are processing information because their input is not the same as their output; they are transforming the former into the latter. Second, this process is computational; 'neurons compute'.

This is a widely held view; psychologist Gary Marcus even wrote about this in the NYT saying 'Face it, your brain is a computer'. In response, Vaughn Bell at Mindhacks posted about this op-ed and this issue in a nicely balanced piece called 'Computation is a lens'. He sums up the issue nicely by asking 'Is the brain a computer or is computation just a convenient way of describing its function?'. The answer, I propose here, is that computation is a fantastically powerful description of the activity of the brain that may or may not be (and probably isn't) the actual mechanism by which the brain does whatever it does. This is ok, because, contra Hickok,  not every process that sits in between an input and a different output has to be a computational, information processing one. 

Non-Specifying Variables in the Perception of Collisions (Specification III)

Part of Withagen's critique of specification and whether it's necessary to underpin direct perception is a brief review of some empirical literature that shows people using non-specifying variables. I want to spend a few posts reviewing these, because all good potentially sensible ideas need data to confirm whether they're right or not.

First up, the perception of relative mass after a collision. Events in the world are dynamic, that is, they involve motion caused by a pattern of underlying forces. Perceptual systems want access to the underlying dynamics of events, because this is the level at which the event is defined (Wilson & Bingham, 2001). However, perceptual systems can only detect kinematics, that is, motion - this is the perceptual bottleneck  (Bingham, 1988 and this note on dynamics and kinematics). We can only perceive the underlying dynamics of an event, according to the ecological approach, if we can detect motion that is specific to that dynamic. Runeson coined the phrase kinematic specification of dynamics (Runeson & Frykholm, 1983) and investigated whether there were such kinematic patterns and whether we can detect them. Working with Claire Michaels and David Jacobs, he has also investigated the use of non-specifying variables.

Gibson vs Physics: Gibson Wins, at the Ecological Scale

One of the interesting questions that popped out of our discussions with Ken Aizawa about Runeson and the Ames Room is this: did Gibson and his followers banish physics and geometry from his psychology? And if so, is Runeson breaking this prohibition by talking geometrically about the Ames Room? And how can you banish physics anyway - what the hell?

I think I've convinced Ken that there is no such prohibition in the comments at the posts linked to above (I think). But it's a topic of fairly central importance to the ecological approach, so I wanted to summarise some of these ideas and examples here.

The Ames Room and the Bower Bird

A recent study (Endler et al, 2010) has shown that bowerbirds take advantage of forced perspective (the Ames Room effect) in the construction of their bowers. This study has a few interesting things to say on the topic of the origin of the Ames Room effect and the likelihood of equivalent configurations popping up by chance. (This article got a lot of popular press when it came out: Ed Yong at Not Exactly Rocket Science covered it best here.)

Runeson, the Ames Room and the Irrelevance of Equivalent Configurations

Recently we’ve been discussing several topics with Ken Aizawa at his blog, The Bounds of Cognition; there are several posts brewing from the two of us on this, but some travelling (plus, for me, a broken wrist) has slowed things a little.

I want to spend some time talking about some recent discussions on aperture vision and the Ames Room. This post will go over two papers on the Ames Room; the next few will discuss some of the more interesting points about the ecological approach that came out of the discussion with Ken. This is a really rich topic, and there’s a lot of ground. First, though, we need the set up.

"Smart" perceptual mechanisms

I mentioned yesterday that James' theory about pure experience being all there is, and relations being legitimate objects for perception does at one level sound crazy. Surely physics is where it's at - if you aren't talking about a physical variable, how can you be talking about anything real?

 Ecological theorists have one good example to hand, courtesy of a 1977 paper by Sverker Runeson, that might help: the polar planimeter (pictured). This is a device that measures area directly, rather than measuring the 'simpler' physical unit length and then performing the necessary computation. Runeson uses this device as an example of a 'smart' mechanism, and proposes that perception might entail such mechanisms.