One of the ongoing "philosophical" points of contention when I was in graduate school was between the cognitive psychologists and the ecological psychologists over the theory of perception.
In a nutshell, the cognitive approach assumes that information in the world is ambiguous and cognitive-perceptual processes are required to interpret stimuli into meaningful information. For example, an object is observed through the visual system and the brain uses that stimulation in conjunction with memory to disambiguate and identify the object. This is in fact how most people understand perception to work.
The minority alternative comes from the ecological perspective ("ecological" as in a rich stimulus environment, and not related to sustainable design), which posits that information in the world is specific and sufficiently detailed to communicate information without any interpretation. That is, the visual stimulus is unique and conveys the relevant characteristics to the observer.
This contrast in approaches also emerged in the world of product and interface design over the term "affordance". The term was coined by J.J. Gibson, the father of ecological psychology, to define the relationship between an actor (e.g. human, animal) and an object or environment. For example, a flat surface "affords" sitting on, a pointy one does not. Note that an affordance is a property that exists whether it is perceived or not or acted on or not.
Following Gibson, the term "affordance" was popularized, but also modified in use by Donald Norman, among others, to emphasize the perception of an affordance (rather than the existence of one). In other words, good design is about effectively communicating affordances to the user.
Now a recent article in Design Studies looks at the issue of affordances vs. perceived affordances in a tangible way - by applying those ideas to the control panel of a stereo system. The paper summarizes the theoretical issues that I have attempted to touch on above, and then illustrates how they are applied to controls. While there are not actionable conclusions from this work, it's an opportunity to understand some of the key theoretical issues in perception and design.
Incidentally, ecological psychologists have more fun.
