p.1 This is a book about how we see. How do we see the environment around us? ...I now believe we must take an ecological approach to the problems of perception.

p.2 What psychology needs is the kind of thinking that is beginning to be attempted in what is loosely called systems theory.

p.17 The medium thus contains information about things that reflect light, vibrate, or are volatile. By detecting this information, the animal guides and controls locomotion.

 If we understand the notion of medium, I suggest, we come to an entirely new way of thinking about perception and behavior.

p.18-19 all these offering of nature, these possibilities or opportunities, these affordances as I will call them, are invariant. They have been strikingly constant throughout the whole evolution of animal life.

p.97 Animals need to perceive the affordances of substances, their chemical values or utilities, in advance of making contact with their surfaces, as I have pointed out before (Gibson, 1966b, Ch. 8)

p.122 How do we see where we are going? We guide or steer our locomotion, when we are in control of it, by locating those invariant features of the array that specify a destination, whatever it may be, and then keeping the focus of optical outflow centered on that item. In short, we magnify the form that specifies the goal.

p.127 Perhaps the composition and layout of surfaces constitutes what they afford. If so, to perceive them is to perceive what they afford.

p.127 The affordances of the environment are what it offers the animal, what it provides or furnishes, either for good or ill. The verb to afford is found in the dictionary, but the noun affordance is not. I have made it up. I mean by it something that refers to both the environment and the animal in a way that no existing term does. It implies the complementarity of the animal and the environment.

p.127-128 They [Affordances] have unity relative to the posture and behavior of the animal being considered. So an affordance cannot be measured as we measure in physics... What other persons afford, comprises the whole realm of social significance for human beings. We pay closest attention to... information that specifies what the other person is, invites, threatens, and does.

p.129 An important fact about the affordances of the environment is that they are in a sense objective, real, and physical, unlike values and meanings, which are supposed to be subjective, phenomenal, and mental. But, actually, an affordance... is equally a fact of the environment and a fact of behavior. It is both physical and psychical, yet neither. An affordance points both ways, to the environment and to the observer.

p.130 Why has man changed the shapes and substances of his environment? To change what it affords him... We were created by the world we live in.

p.134 Orthodox psychology asserts that we perceive these objects as we discriminate their properties or qualities... I now suggest that what we perceive when we look at objects are their affordances, not their qualities... what the object affords us is what we normally pay attention to.

p.140 The theory of affordances is a radical departure from existing theories of value and meaning. It begins with a new definition of what value and meaning are. The perceiving of an affordance is not a process of perceiving a value-free physical object to which meaning is somehow added in a way that no one has been able to agree upon; it is a process of perceiving a value-rich ecological object. Any substance, any surface, any layout has some affordance for benefit or injury to someone. Physics may be value-free, but ecology is not.

 The central question for the theory of affordances is not whether they exist and are real but whether information is available... for perceiving them.

p.141 An affordance, as I said, points two ways, to the environment and to the observer. So does the information to specify an affordance... the information to specify the utilities of the environment is accompanied by information to specify the observer himself

p.141 The child begins... by perceiving the affordances of things for her, for her own personal behavior... But she must learn to perceive the affordances of things for other observers as well as for herself. An affordance is often valid for all the animals of a species

p.142 If the affordances of a thing are perceived correctly, we say that it looks like what it is. But we must, of course, learn to see what things really are - for example, that the innocent-looking leaf is really a nettle or that the helpful-sounding politician is really a demagogue. And this can be very difficult.

p.143 the basic affordances of the environment are perceivable and are usually perceivable directly, without an excessive amount of learning. The basic properties of the environment that make an affordance are specified in the structure of ambient light, and hence the affordance itself is specified in ambient light. Moreover, an invariant variable that is commensurate with the body of the observer himself is more easily picked up than one not commensurate with his body.

p.143 The possibilities of the environment and the way of life of the animal go together inseparably. The environment constrains what the animal can do, and the concept of a niche in ecology reflects this fact. Within limits, the human animal can alter the affordances of the environment but is still the creature of his or her situation.

p.198 Animals and humans are capable of being oriented to the habitat. This state is the opposite of being disoriented or "lost." ...Both animals and humans... are capable of way-finding... A vista is what is seen from here... To go from one place to another involves the opening up of the vista ahead and closing in of the vista behind. A maze or a cluttered environment provides a choice of vistas... When the vistas have been put in order by exploratory locomotion, the invariant structure of the house, the town, or the whole habitat will be apprehended. The hidden and the unhidden become one environment... One is oriented to the environment.

p.236 a great deal of manipulation occurs for the sake of perceiving hidden surfaces.

p.238 In this book the traditional theories of perception have been abandoned.

p.239 What sort of theory, then, will explain perception? Nothing less than one based on the pickup of information... Let us remember once again that it is the perception of the environment that we wish to explain.

p.239 The theory of information pickup differs radically from the traditional theories of perception. First, it involves a new notion of perception, not just a new theory of process. Second, it involves a new assumption about what there is to be perceived. Third, it involves a new conception of the information for perception, with two kinds always available, one about the environment and another about the self. Fourth, it requires the new assumption of perceptual systems with overlapping functions, each having outputs to adjustable organs as well as inputs from organs. We are especially concerned with vision... Finally, fifth, optical information pickup entails an activity of the system not heretofore imagined by any visual scientist, the concurrent registering of both persistence and change in the flow of structured stimulation.

p.239-240 A Redefinition of Perception
 Perceiving is an achievement of the individual, not an appearance in the theater of his consciousness. It is a keeping-in-touch with the world, an experiencing of things rather than a having of experiences. It involves awareness-of instead of just awareness... Perceiving is a psychosomatic act, not of the mind or of the body but of a living observer.
 The act of picking up information, moreover, is a continuous act, an activity that is ceaseless and unbroken. The sea of energy in which we live flows and changes without sharp breaks... perceiving is a stream... The continuous act of perceiving involves the coperceiving of the self.

p.240 A New Assertion about What is Perceived
 My description of the environment and the changes that can occur in it implies that places, attached objects, objects, and the substances are what are mainly perceived, together with events, which are changes of these things. To see these things is to perceive what they afford.

p.241 So when it comes to the natural, nonrigid, animate objects of the world whose dimensions of difference are overwhelmingly rich and complex, we pay attention only to what the animal or person affords.

p.242 The Information for Perception
 Information, as the term is used in this book (but not in other books), refers to specification of the observer's environment, not to specification of the observer's receptors or sense organs. The qualities of objects are specified by information; the qualities of the receptors and nerves are specified by sensations. Information about the world cuts right across the qualities of sense.
 The term information cannot have its familiar dictionary meaning of knowledge communicated to a receiver. This is unfortunate, and I would use another term if I could... [I] ask the reader to remember that picking up information is not to be thought of as a case of communicating. The world does not speak to the observer... the information in the sea of energy around each of us... is not conveyed. It is simply there.

p.243 Shannon's concept of information applies to telephone hookups and radio broadcasting in elegant ways but not, I think, to the firsthand perception of being-in-the-world... The information for perception, unhappily, cannot be defined and measured as Claude Shannon's information can be.

p.244 The Concept of a Perceptual System
 The theory of information pickup requires perceptual systems, not senses.

p.245 the achievements of a perceptual system are susceptible to maturation and learning... The information that is picked up... becomes more and more subtle, elaborate, and precise with practice. One can keep on learning to perceive as long as life goes on.

p.246 The Registering of Both Persistence and Change
 The theory of information pickup requires that the visual system be able to detect both persistence and change - the persistence of places, objects, and substances along with whatever changes they undergo. Everything in the world persists in some respects and changes in some respects. So also does the observer himself. And some things persist for long intervals, others for short.

p.249 Summary of the Theory of Pickup
 According to the theory being proposed, perceiving is a registering of certain definite dimensions of invariance in the stimulus flux together with definite parameters of disturbance. The invariants are invariants of structure, and the disturbances are disturbances of structure. The structure, for vision, is that of the ambient optic array.

p.250 The process of pickup is postulated to be very susceptible to development and learning... The ability to perceive does not imply, necessarily, the having of an idea of what can be perceived.

p.251 The theory of information pickup purports to be an alternative to the traditional theories of perception. It differs from all of them, I venture to suggest, in rejecting the assumption that perception is the processing of inputs.

p.253 Knowledge of the environment, surely, develops as perception develops, extends as the observers travel, gets finer as they learn to scrutinize, gets longer as they apprehend more, gets fuller as they see more objects, and gets richer as they notice more affordances. Knowledge of this sort does not "come from" anywhere; it is got by looking, along with listening, feeling, smelling, and tasting.

p.254 The state of a perceptual system is altered when it is attuned to information of a certain sort. The system has become sensitized. Differences are noticed that were previously not noticed. Features become distinctive that were formerly vague.

[JLJ - Consider the typical morning rush-hour drive to work. I can listen to this radio station, or that radio station, or turn the radio off completely. But if I listen to the radio station that contains traffic information, I may hear of an accident up ahead and change the route that I take to work. If I am not listening to the traffic report, I will continue along as usual until I see a backup ahead. By then it might be too late to change my route to work. "The state of the perceptual system is altered when it is attuned to information of a certain sort." A report of an accident ahead, delivered on a reliable radio station, is enough to cause me to change my behavior. I do not yet see the accident, I do not yet see the backup, but I perceive a clue that it is almost certain to impact me, and therefore worth responding to.

Gibson is implying that perceptual systems are attuned to certain types of information in the environment, much like a dog sniffing the ground on its morning walk, and alter their behavior upon receipt of what I refer to as cues/clues. There is only the detected cue/clue. BUT we deem that this almost certainly IMPLIES the possibility (at least) of something much more, the residue or presence of something 1. unseen in completeness or 2. in process of formation, which is or might be important, and ought to be responded to in a certain way. Think of a businessman establishing "critical success factors" for his business, and monitoring them. One of these established factors now starts to lag, and in fact has just dropped in score on some sort of measured scale. The businessman now decides to investigate, make it a priority, and to monitor/adjust the projects that he has developed to ensure that this parameter stays within limits. The other critical success factors he will monitor less often, or perhaps delegate to another trusted adviser, or take resources from, since they do not appear to be of critical concern at the moment.

We seem to have arrived at the holy grail of machine-based game playing. We need to tune the perception of the machine to information of a certain sort, and to change our exploration behavior (of the future consequences) in certain ways based on the information that we pick up. That is it in a nutshell. Case closed. Go get a beer and watch some TV. Oh, I just forgot. Those details are in themselves difficult to resolve, and the subject of much research and development. Rats. Put the (unopened, else it otherwise would have to be consumed) beer back in the fridge, turn off the TV. Get back to work.]

p.255 To expect, anticipate, plan, or imagine creatively is to be aware of surfaces that do not exist or events that do not occur but that could arise or be fabricated within what we call the limits of possibility.

p.256 I suggest that perfectly reliable and automatic tests for reality are involved in the working of a perceptual system. They do not have to be intellectual.

p.257 The most decisive test for reality is whether you can discover new features and details by the act of scrutiny. [JLJ - no, the most decisive test for reality is submitting an article to an academic journal for consideration for publication. If your article is rejected with unkind comments (and a low numerical score which indicates that it is of little concern), you are in reality. If it is accepted, you are not.]

p.258 Knowing is an extension of perceiving. [JLJ - knowledge is just a good guess at what we would observe if we ran up to something, touched it, pressed it, pushed it, asked it questions, tried to trick it, kicked it, laughed at it or tried to sell it something or take something from it or take it apart or went behind it or turned it on or off, or watched what would happen next. It is a substitute for all these things -- that we might just have to rely on in a pinch -- but we could confirm if we had to.

But knowledge helps us make decisions by helping us to simulate how something is going to turn out, and so we can prepare for the unexpected in ways that make sense. It makes sense to lock your door when you leave your house - it does not make sense to nail and hot-glue it shut. Chances are, no one will break in, and you will just find it inconvenient to repeatedly get in and out. Knowledge helps you decide when something or some solution is "good enough" so that you can usually forget about the unexpected happening and causing you grief, and you can get on with other things.]

p.258 But I can think of three obvious ways to facilitate knowing, to aid perceiving, or to extend the limits of comprehension: the use of instruments, the use of verbal descriptions, and the use of pictures. [JLJ - or to execute a diagnostic test and observe the results. In certain cases we need to decide what to do next. A diagnostic test provides an answer - that just might be correct.]

p.260 Knowledge that has been put in words can be said to be explicit instead of tacit.