Eyes are for seeing and noses are for smelling. Everyone knows this. You know this. But hold on, what’s this? Ecological psychologists think you’re wrong!
The problem goes like this. Animals have to move about in an environment that already has other stuff in it besides the animal itself. All kinds of stuff. Imagine you’re a fish. You want to get over there to swallow that clod of plankton. If this was a video game you’d just press buttons until the plankton clod got big and filled up the screen. And when you can’t make the plankton clod look any bigger, that’s when you know you’ve arrived. Good old-fashioned visually-guided locomotion. But things aren’t that simple. You’re a fish, and there’s water in the way. Now you also have to move in such a way as to cancel out the movement of the water. Also, since you’re a fish, that is, a living, active organism, the visual scene before your eyes is in part structured by your own movements. Now you have to work out which bits of the stuff you’re looking at are moving because stuff out there is moving, and which bits are moving because you’re a fish and you’re twitching your face from side to side and your paddling is creating weird ripples and shadows.
One way to respond to this is to shrug and say, “I dunno, being a fish is complicated, I guess. At least they don’t have to worry about table manners or heights.” This is the normal way to respond. If you’re an ecological psychologist, however, you might respond differently. You might come out with something like this: “We propose that the senses form a single, unitary, irreducible perceptual system whose sole function is to detect parameters of the global array.”
In making this proposal, Stoffregen, Mantel, and Bardy are doing us a service for they are forcing us to question an unexamined assumption. In this case, the assumption is that the senses constitute distinct and separate systems. As the authors note, James J. Gibson also liked to question unexamined assumptions. But Gibson himself accepted this particular assumption without examining it. According to SMB, this has led to problems. One such problem: research within the ecological tradition has asked questions of the form, “What visual parameter is implicated in controlling the movement of this seabird into this body of water?” But this reductively detaches the visual component of the behaviour from everything else that is going on in the bird–air–water–gravity–etc. system.
A more esoteric problem is this: specification of structure in the environment into structure in perception does not work if we consider the senses as distinct systems. If all the seabird has to go on is vision, then it has no way of distinguishing between changes in the appearance of the water surface that are caused by its movements towards the surface, and those that are caused by the movement of the air relative to the same surface. Without being able to distinguish between these, SMB claim, the bird cannot adjust its behaviour over time in the appropriate way. Specification only works if we consider all of the relevant structure at once. And we need specification. Ambiguity is no good. If specification fails, then direct perception is also impossible, and ecological psychology itself disintegrates into an incoherent puddle.
Now, it is tempting to respond to SMB’s proposal that the senses constitute a single, unitary system in this manner: “Nuh-uhh! The senses are obviously separate! Look! Eyeballs!” But SMB have been making this argument for a few years now and have apparently come across this response before (S&B originally published this argument in BBS in 2001; the 2017 paper is largely a reassertion of that one). The authors call for their critics to go beyond merely pointing out apparent instances of counter-evidence and to engage with their arguments “at the level of general principles”. So let’s try to do that. I will make three points.
First, while every assumption deserves to come under scrutiny once in a while, it’s impossible to evaluate any given assumption except in the light of remaining assumptions that we hold to be more fundamental or secure. Thus, SMB state:
If we accept that perception yields knowledge (i.e., that perception is epistemological), then we can ask what type of knowledge is obtained. Following Darwinian principles … Gibson reasoned that perception yields (and should yield) knowledge about the environment.
But wait, what? Why should we accept this assumption? I mean, not to be rude, but “perception yields knowledge”… that sounds a little, I dunno, Cartesian? SMB also talk about perception as having content: “Our focus is on the animal–environment interaction as the contents of perception”.
Maybe the real problematic assumption here is this one: that information is contentful, i.e. that it is about structure in the environment. This argument was made by Van Dijk, Withagen, & Bongers in a paper that I blogged about here. If information is contentless, then the issue of ambiguity does not arise. Ambiguity is not in the information because information is not being transmitted. The animal is not in the business of constructing knowledge about what the world has in it. Rather, the animal is in the business of regulating the fit between itself and its environment. If this is the case then perception does not have to be infallible, it just has to be good enough to keep the animal alive for a certain while. The fit is either maintained, in which case the animal is still alive, or it isn’t, and it’s dead. But why say that this fit is the content of perception?
Second, in their enthusiasm to do violence to the Aristotelian dogma of separate senses, SMB sometimes risk doing damage to other theoretical distinctions which we presumably want to maintain. For instance, it seems useful to distinguish between a) action and b) structure in the environment with reference to which that action is being regulated. In their more effusive moments SMB seem to want to fold this all together:
The global array is not ambient to massless, geometric points; rather, it intrinsically, inescapably is ambient to and provides information about the full dynamics of the animal–environment interaction. The global array pulses with the life of the organism; it embodies animal–environment reciprocity.
SMB argue that Gibson’s notion of the ambient optic array as a set of points of potential observation is “disembodied” and “reductionist”, and we should instead think in terms of an “embodied point of observation”. We should recognize that visual information in real life is structured simultaneously by stuff in the environment and by the activities of the living, moving animal itself. When you walk, your eyeballs jiggle in your head, which is going up and down on top of your neck thump-te-thump. This is fine, but don’t we also still want to be able to talk about structure that’s actually out there in a straightforward way, without constantly having to talk about it in terms of the animal–environment fit?
Third, and more generally: suppose we all went along with SMB and just admitted that the notion of separate senses is mere superstitious hokum and baloney that has been holding us back from pursuing a properly scientific study of perception. Where would that actually get us? In what way is it useful to treat perception as a single system? It certainly seems useful to treat vision, say, as a distinct system. To do so is consistent with our everyday conception of our experience—our way of talking about it. Don’t we want to be able to explain, say, the navigability of the inside of a building in terms of what it looks like without having to also talk about what the air feels like on our faces or what smells are wafting in from a nearby cafeteria? How does it help us to flat out deny the distinctions we have traditionally made between the senses?
It’s hard to see the global array concept getting any real uptake based only on arguments that have been presented so far. What would make the case more convincing? SMB need to show either that the assumption of distinct senses is pernicious and has misled us in important ways, or that rejecting the assumption leads to useful outcomes or applications that would otherwise be inaccessible to us. They have done neither of these so far. Maybe they’re right, though. I’m going to ask a fish.
Stoffregen, T. A., Mantel, B., & Bardy, B. G. (2017) The senses considered as one perceptual system. Ecological Psychology, 29(3):165–197 doi: 10.1080/10407413.2017.1331116