A little history, by way of introduction

I’m a Gibsonian. I study perception and action from an ecological perspective, which is based in James Gibson’s theories of perception (and Nikolai Bernstein’s theories of motor control). This perspective is, in many ways, in direct conflict with the dominant cognitive paradigm in psychology, and frankly a lot of people simply think it’s ridiculous. This is partly our own fault: the ecological camp is small, a bit insular and prone to picking odd fights. But I think we are right, even if sometimes I don’t think we’re studying it or talking about it right. My goal for this blog is to work some of these thoughts out (amongst other things) so I can actually turn these thoughts into experiments and papers.

The main driver for me doing this right now is an internal argument that is brewing amongst ecological types that I think is a) flawed and b) a waste of time. I’ve been thinking and talking about this conflict for a little while now, but I need to find ways to go after the flaws empirically: I am a scientist, and in spite of all the evidence I really do believe psychology can be a science. The argument is actually yet another round of the only argument that ever happens about perception: what constitutes information for a perceiving organism? The modern Gibsonian approach makes specific claims about this, so before we get into the recent stuff we need some context. That means we need a little history.

A Little History

The fundamental question in perception is, what is the information for perception? What is the form of the proximal stimulus (the thing that actually causally interacts with an organism’s sensory apparatus)? The answer to this question has almost always been that the proximal stimuli are sensations, meaningless physical events (photons for vision, compression waves for hearing, etc). Sensations are meaningless because they do not fully specify the world that caused them; they are ambiguous, because a given physical event gives rise to many patterns of sensations (a small red ball flying towards you produces a different optical pattern than, say, a large blue ball, although they are both the same type of event).

The basic ‘sensation based theory of perception’ runs as follows:

a. Something happens in the world (the distal stimulus). This is what an observer eventually needs to respond to, and so needs to detect it somehow.

b. This event causes a pattern of change in the light, although this pattern only correlates with the event in the world; local conditions, the observer’s perspective, etc, alters many of the details.

c. An observer detects this pattern (the proximal stimulus) which is related to the event in the world but not uniquely.

d. They must then infer what event in the world lead to this pattern (i.e. resolve the ambiguity).

e. The observer then responds appropriately to the event.

Modern cognitive psychology has what is essentially just the latest version of this hypothesis, in which it fills in some of the details. (a) and (b) remain the same: these are taken to be the facts of the matter (and it’s the correlation aspect in (b) that Gibson will object to):

c. The proximal stimulus (for vision) is the ‘image’ projected to the back of the eye, onto the retina. Like a camera, the eye focuses rays of light (photons) to a point (the fovea) and forms an image. The image isn’t really a picture (not in modern theories, although people still talk about the retinal image); it’s a pattern of light distributed across the retina. There are internal correlations between the ‘pixels’ such that neighbouring pixels tend to resemble each other, unless there is an edge, in which case they differ immensely (telling you there’s an edge there). However, this image is ambiguous with respect to what caused it; there is a one-to-many mapping, in which one event could lead to multiple patterns (every visual illusion is an example of this).

d. The job of vision is to resolve this ambiguity, via inference. Essentially, the solution to this problem is that the visual system must make an educated guess about which of the ‘many’ possible events caused the ‘one’ proximal stimulus. The education of the guess comes from mental representations, the workhorse of cognitive psychology. A representation is a pattern of neural activity/connections that ‘stands in for’ (i.e. represents) the missing information. The representation may contain information about past exposure to this pattern and what the event turned out to be (learning); it may contain information about how certain types of correlations tend to indicate one thing or another. Visual perception is the cognitive process of detecting the proximal stimulus, then selecting and applying the correct representations from your repertoire to resolve the ambiguities.

Cognitive theories about visual perception therefore

1. assume a poverty of stimulus, i.e. an ambiguous proximal stimulus that must be enriched with internally stored information, and

2. are about uncovering the contents of the representations and how the correct one(s) are selected and used.

This is the state of things today, and is the essential form of the argument that James Gibson rejected with his theories. Gibson’s move was simple: he considered (b) from above, and rejected it. If the proximal stimulus only correlates with events in the world, he said, then perception is doomed to failure – how do we ever build correct representations? How could we possibly select the right ones? Gibson’s solution was to rethink information, and propose that events in the world can, in fact, lead to changes in patterns of light that uniquely specify the event that caused them, rather than merely correlate with. He also argued that it couldn’t be any other way, if perception was to ever work the way we experience it working every day. The next step is to consider some details of Gibson’s alternative.