Notes for Tuesday Class

Notes on Gibson, 1960 (assigned for and discussed at the last class)

  1. 701 – “An effective stimulus can now be defined. It is one which arouses receptor activity, or recorded neural impulses, or sense organ adjustments, or overt responses, or verbal judgments – whichever criterion one chooses. . .

“In short, whether or not a potential stimulus becomes effective depends on the individual.”

Beth noted that this seems to be just as eclectic as the variety of positions Gibson was reviewing.  Therefore, it didn’t seem like he was taking such a definite position after all.

I don’t want to leave this hanging.  Gibson would not be especially happy about this way of putting the matter later on, but there is a point that’s largely consistent with what he’s saying and will continue to say.  First the large presupposition of the last sentence quoted – Gibson endorses the idea of potential stimuli and does not want to limit the definition of stimuli only to effective stimuli.  Second, the main point here – if an effective stimulus can be defined relative to a receptor, or a neural impulse, or sense organ adjustments, or overt responses, it means that there is no single level that is the stimulus.  If, for example, a ray of light can be said to fire a cone receptor in the retina, it does not mean that only rays of light can be considered stimuli and that every other feature of experience is the result of operations adding together and operating on the receptor responses to many stimuli.

This leads us naturally to the considerations in the 1959 chapter.

Notes of 1959 chapter

Keep in mind that for most scholars of perception, whether they are philosophers, physiologists, or experimentalists, the fundamental experiences that animals have as an immediate function of stimulation is something usually called a sensation  — like a meaningless patch of color. Philosophers called these “sense data.”  The primary presumption is that the psychological effects of stimuli are very different from our “everyday” experiences of the world.  Stimuli for vision are, for example, light rays, and we experience solid surfaces, open spaces, other people, and so on. The experiences of our meaningful world are a far cry from the stimuli at our receptors.


Much of perceptual theory, and cognitive theory, is devoted to hypothesizing and investigating the “filling in” processes – whatever has to happen to explain the experiences we ultimately have.  The whole enterprise is based on theories of stimuli that guarantee that they are nothing like what we finally experience.


But Gibson was questioning the basis for people’s certainty that they knew enough about what stimuli were to know that they definitely would not the basis for our experiences.  If you can question what counts as a stimulus, and do research on it, then it’s not necessarily the case that there is a gap between stimuli (what is given) and what is experienced.  That’s huge.


It then becomes possible to imagine Gibson’s formula – “that perception is a function of stimulation and stimulation is a function of the environment (p. 463),” and therefore that the environment is the object of perception.


Consider Gibson’s DEFINITION of perception:  The word perception in this essay means the process by which an individual maintains contact with his environment (p. 457).”    You won’t find anyone else who defines that as the issue.  Can you find other definitions of perception?


Later for students:


Look at some of the pictures from Gibson’s 1950 book, inspired by looking at the earth from airplanes.


What is an object (in the topic of object perception)?  Then:  Is the ground an object?  How much of it?  Does it have a shape?  Is the sky an object?  Where are they?  Is the horizon an object?  Where is it?  Are these weird?   Who talks about them?  Do you see air?  How do you know where to walk?


In 1950, Gibson called his theory a GROUND theory and then called the opposing traditional theories, AIR theories.

Psych 493 Syllabus