A blog about problems in the field of psychology and attempts to fix them.

Monday, March 1, 2021

Defining key terms in Ecological Psychology

Andrew Wilson and I had a tiff on twitter about whether "Affordances" are by-definition "perceivable". Well... backing up... it was a tiff about whether it is fair for a researcher to start talking about something as an example of an affordance, when they have not bothering to demonstrate that the thing in question is perceived. This actually has deep implications for all the key terms in Ecological Psychology. As it is the type of thing you can't really discuss in 240 characters, we decided to return to the blogosphere. Who knows, maybe we can crank out a second blog-driven co-publication when this is done!*

I am extremely sensitive to the problems that occur in a theory when terms start to get mutually inter-defined. You quickly end up with tautologies, and tautologies stop your theory from being a theory in any proper sense. My post-doc advisor and occasional co-author Nick Thompson wrote about this problem extensively in the context of learning theory and evolutionary theory and other contexts in psychology. I don't think any prominent members of the Eco Psych community have such a problem when they are doing research. However, when they start writing theory, the problem pops up fairly often, and it is behind many of the long-term disputes in the literature. The temptation to inter-define terms is strong, because when terms are mutually defined, deduction is easier, and that makes the theory feel intellectually safe and well-founded. However, that feeling is misleading in a scientific context. you can't test things that are deducible from each other, so if you find yourself just stating things that are true by definition, you don't have a theory anymore, because the exact part this is supposed to be testable can't be tested. The way out of this is to rigorously ensure that your terms point to things that can be verified independently of each other, leaving it open for testing whether the things in question relate in the manner proposed. 

My last paper in the journal Ecological Psychology, "Essential Elements of an Evolutionary Theory of Perception"** was, in a large part, directed towards untangling the tautology problem so I'm going to draw heavily on that here. 

Structured Energy - "Invariants":

Gibson's system is "Ecological Psychology" because he speculated about the existence of a hitherto unrecognized aspect of ecology, the structure in ambient energy arrays. Perceptual systems evolved (and develop) as adaptations to that aspect of their environment. 

  • The objects and events in the world create all sorts of structure the ambient energy. 
  • Some of that structure is specific to properties of the objects/events, other structure is commonly associated with certain objects/events, and still other structure is - for lack of a better term - random. 
  • Specification cannot be in a projective image (as has been well established for centuries), but specification can exist in higher-order structures of the ambient energy. Those are commonly referred to as "invariants" or "higher-order invariants." 
  • We can identify higher-order invariants that specify properties of the environment purely mathematically, or discover them empirically. The second-order moment of inertia may specify the length of a wielded rod, the rate of optic (or acoustic) acceleration may specify time to impact, etc. 

Perceptual Systems:

Because Gibson's approach views perception as an adaptation to structures that exist over space and time, Gibson views the perceptual system as virtually whole-organism. 

  • Perception and action blend together, as part of a larger dynamic system, because movement will not only be a result of perception, it will be a driver of perception. 
  • For example, if I don't move the rod, I cannot detect the second-order moment of inertia, and only certain types of movements will allow for that perception. Similarly, if I stay in exactly the right place, I will be unable to tell the difference between my child doubling in size and my child moving to the other end of an Ames room, but the right movements easily allow my perceptual system to "resonate" with the higher-order invariants that specify which situation I am in. 
  • Learning to behave and learning to perceive are thus intimately intertwined. 
  • We can study the activities of perceptual systems without reference to the above concept. 
  • We can study behavior, including the movements of perception, by placing the organism in various situations and seeing how they move. For most tasks, organisms that move in certain ways will be found to be more accurate in tasks than those that move in different ways. That suggests such movements promote accurate perception. 

Gibson coined the term "affordances", to refer to opportunities for action that exist in the environment. 
  • Certain situations afford the production of certain outcomes, by organisms with certain properties. 
  • A human, a racoon, and an elephant might all be able to open a front door, but the open door does not afford a house-entering for the elephant. The door-with-doorknob set up does not afford door-opening to a slug or a blue jay. 
  • We can study affordances without reference to any of the above concepts. 
  • For many affordances we can simply measure the environment and measure the organism (e.g., can the elephant fit through my front door). For others we will need to measure the organism's abilities in various ways (e.g., I can jump up on surfaces higher than most people my height, but some people can jump much higher than I can). 
Gibson's THEORY

Gibson proposed that organism evolve and develop so that their perceptual systems pick up invariants that specify affordances. 
  • Perceptual systems frequently cannot pick up invariants that specify affordances, when it would be quite useful for the organism to be able to. 
  • Invariants exist that specify aspects of objects/events that do not afford anything to any organism that currently exists, or ever will.
  • There are affordances that are imperceivable, either because they do not structure ambient energy sufficiently, or because the relevant organisms lack perceptual systems capable of detecting them. 
  • But sometimes it all lines up. Sometimes -- often even! -- organisms pick up invariants that specify affordances, and that veridical perception guides skilled behavior to the successful realization of the organism's goals. The diving bird, attuned to "Tau", perfectly times its contractions to pierce the water, and it grabs the fish. If the fish got away, it could try again, but if the piecing-contraction was mistimed, the impact with the water could be fatal. 
The proposed relationship between things that can be defined independently of each other is what makes the Ecological Approach a theory. Gibson claimed that if we spent enough time and effort studying the structure of ambient energy arrays, and enough time and effort studying the perceptual systems of organisms, and enough time and effort studying affordances, and enough time and effort studying the relationship between those things, we would be able to evidence that they fit together to create a larger story, much of the time. 

What would happen if we defined affordances as oportunities-for-action-specified-by-invariants-and-infallibly-detected-by-perceptual-systems? And defined invariants as patterns-that-specify-afforadances-and-are-infallibly-detected-by-perceptual-systems? And defined perceptual systems as the-parts-of-the-organism-that-infallibly-detect-invariants-that-specify-affordances? If we do all that, we will have taken the basic empirical claims of the theory -- the hypotheses intended to drive scientific discovery -- and turned it into some sort of word game, something that is a matter of definition, not evidence. 

Gibson didn't make that mistake. He did not argue that all perception was perfect, nor did he try to render perception as perfect by wordsmithing the definition. He argued that the new-level of ecology he described -- structured energy arrays -- made veridical perception possible, and argued that his work on perceptual systems and research into perception-action coupling evidenced that it was not only possible, but routine. The normal, mundane behaviors that get all of us through our day rely on our perceptual systems picking up invariants that specify affordances, as does highly-complex skilled behavior. And we know that because we can identify invariants, affordances, and perceptual systems independently of each other, and then study how they relate. 

* Charles, E. P., Golonka, S. & Wilson, A. D. The Most Important Thing Neuropragmatism Can Do: Providing an Alternative to ‘Cognitive’ Neuroscience. In Pragmatist Neurophilosophy: American Philosophy and the Brain, J.R. Shook & T. Solymosi, Eds, pg 127-149.

** Charles, E. P. (2017). The essential elements of an evolutionary theory of perception. Ecological Psychology, 29(3), 198-212.




  1. I'm curious whether you think this implies anything for the principles of mutualism or reciprocality that ecological psychology (and enactive thinking) places so much emphasis on.

    Where the perspective depends on a recognition of holism in the system overall, can any definition be maintained with the clear distinctness you require here?

  2. I appreciate how you breakdown and define the key terms of ecological psychology. This article is quite beneficial to many.

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