The first key paper of the modern science is probably a paper on perceptual learning (Gibson and Gibson, 1955), in which it was proposed that perceptual learning involved better discriminating stimuli. That is, this type of learning does not involve gaining more sophisticated mental processes, but rather more sophisticated sensitivity to the details of the world. Discussion generated by this paper, and further related works, were guided by a search for the 'discriminated thing' needed to fill in the perceptual-learning theory. The most obvious candidate would be something like the stimulation created by the retinal image... but the problem with the retinal image were already well known: The retinal image is not specific to the properties of the world, and therefore it cannot provide a firm basis for accurate perception. Gibson's prior work on optic flow was working towards a solution, but something more radical was needed.
This culminated in the second key paper (Gibson, 1961), in which it was pointed out that we could study the ecology of ambient energy, i.e., the structure of the light waves, sound waves, etc. that are bouncing all around you in whatever room you are reading this in. The visual side of this work would be called Ecological Optics, and from that we get the 'ecological' in 'Ecological Psychology'. The structured energy around us is specific to the properties of the world, and so if we can discriminate this ambient energy in the right ways, we come to know the properties of the world. Or, if we want to back off just a touch: At least some of the structure in the ambient energy is specific to at least some of the aspects of the world we would like to know about, and so, in those moments when we managed to correctly discriminate the correct pattern-structures, we are accurately and unambiguously discriminating something about the objects and events around us.
A few years later this idea was put into the a book-length discussion of the evolution of perceptual systems, which include both the sensory organs and all the other parts of the organism involved in moving so as discriminate these patterns (Gibson, 1966). The evolutionary context in which human abilities are thereby put, and the developmental context that started this whole line of thinking, led to some speculation in the final chapters about what aspects of the world we would expect organisms to perceive: Evolution and development both occur in the context of behavior, and so we might expect organisms to evolve and develop so that they discriminate those aspects of the world relevant to behavior. That is, we would expect animals (including people) to be best at discriminating the world in terms of what it affords them, e.g., in terms of what future actions the current situation makes possible, e.g., in terms what outcomes can be realized by the actions the animal is capable of performing. To make this concept more concrete, Gibson invented the term 'affordance.'
Still later (Gibson, 1979), the more radical consequences of this new understanding of perception were explored at length. Gibson had been a very well reputed perceptual researcher in the '40's and '50's, before any of this ecological thinking began, but by the time of his last book there were a growing number of people interested in pursuing the more aggressive research agendas he had laid out. The most obvious research tasks were: 1) Identify higher-order invariants that specify properties of the world, 2) Show that organisms (these days, typically 'people') are sensitive to those invariants, 3) Put those together into demonstrations that behavioral success is due to proper sensitivity to invariants. Oh, and 4) don't shy away from opportunities to do this in the context of tasks not traditionally thought of as 'perceptual.' The most important early proponents of Gibson's thinking were Michael Turvey, Bob Shaw, and Bill Mace, who played pivotal roles in founding the International Society for Ecological Psychology, the journal Ecological Psychology, and the Center for the Ecological Study of Perception and Action (CESPA) at the University of Connecticut. David Lee made the first solid demonstration of an optical invariant used to guide a critical behavior - the rate of acceleration of optic expansion (symbolized 'tau'), which can be used to regulate timing of impact with a surface. Initial studies looked at birds retracting their wings when diving into water at break-neck speeds, and modern studies span things as diverse as the control of force in punching and better understanding how people control their cars while breaking. Clair Michaels and Claudia Carello put out the first book that could be considered a textbook for the field "Direct Perception." It is now outdated not so much by advances in theory, but by lack of including the three decades worth of research success since its publication.
Today, Ecological Psychology has a small, but thriving research community using this approach to study the full range of psychological phenomenon.
Some notes (perhaps especially relevant to those interested in the Eco-psych textbook project):
- Many presentations of Ecological Psychology start with 'affordances', but I think that is a mistake. That organisms typically (or perhaps always) see the world in terms of opportunities for action, falls naturally out of an evolution and development focused approach to perception.
- There is a less extreme form of Ecological Psychology worth advocating, the one that uses the words like 'most' or 'typically' instead of 'always'. Many of the problems with Eco-psych being accepted in more mainstream contexts have to do with that pesky 'always'. At the least, get people onboard with the 'sometimes' first, and then the 'typically'. We can suggest the 'always' later... especially if your target audience is not into deep philosophy.
- The presentation above spent very little time (only a sentence or two) explaining alternative approaches to Eco-psych. This is similar to the format I hope the textbook can take. Lead with the ecological way of thinking, and avoid, to the extent possible, teaching students the way you do not want them to think about perception.
- The above presentation goes in historic order, which I'm not convinced is the best way to introduce the concepts to undergraduates. I have used the above order successfully with grad students and colleagues, but with the undergrads especially it seems something better could be done. Apparently past attempts at an Eco-psych textbook (Stoffregen tells me) were derailed before they even began by disagreements about what order things should appear in. If you're reading this, and wishing you could think of something to comment on.... What do you think is the best place to start?