Times Literary Supplement JUNE 23, 1972 1 Seeing as thinking: questions, with hearing the runner- up, for sight dominates by its an active theory of giving us immediate external perception reality. By simply looking we seem to understand what we see. Richard Gregory This close association between seeing and knowing makes the Theories of perception – of what sense of vision attractive not only happens to bridge the to philosophers but also to extraordinary gap between sensory experimental psychologists and stimulation and our experience of physiologists who hope to discover external objects-have a long in the brain mechanisms serving history, of astonishing variety. our experience and knowledge of Speculation goes back to the the world. By coming to beginning of recorded philosophy- understand how we see might we and scientific work on perception not at one stroke also discover how escapes the philosophical we think, remember, formulate questions and dilemmas only when hypotheses, appreciate beauty and- it narrows inquiry by over- most mysterious accept pictures blinkering specialization. How we and words as symbols conveying see remains essentially mysterious not merely present reality but other after a century of intensive realities distant in space and time? experiment, by such a variety of And if seeing involves all this, scientists that aims and surely the net of understanding communication can be lost must be cast wide. between them. An adequate Perceptual theories form a theory should include not only the spectrum -- from passive to active favoured sense of sight but also: theories. Passive theories suppose hearing, touch, hot and cold, taste, that perception is essentially smell, balance and position of the cameralike, conveying selectcd limbs, the various kinds of pain; aspects of objects quite directly, as and tickle, from its irritation to though the eyes and brain are sensuous pleasure and delirious undistorting windows. The baby, laugh – making. it is supposed, comes to see not by using cues and hints to infer the To the philosopher and the world of objects from sensory data experimental scientist, it is how we but by selecting useful features of see that offers the most exciting Times Literary Supplement JUNE 23, 1972 2 objects available to it directly; acceptable as a scientific theory. It without effort, information fits well with – and indeed processing or inference. Active essentially is -- the familiar theories, taking a very different "stimulus/response" notion in view, suppose that perceptions are which behaviour is described as constructed, by complex brain controlled directly by prevailing processes, from fleeting conditions. This is also familiar in fragmentary scraps of data engineering : in most devices input signalled by the senses and drawn directly controls output ; and much from the brain's memory banks - emphasis is put on measuring input themselves constructions from and output, and relating them by snippets from the past. On this transfer functions or something view, normal everyday perceptions equivalent, to describe the system. are not selections of reality but are B. F. Skinner in his behaviourism rather imaginative constructions - claims to do much the same -- to fictions-based (as indeed is science give at least a statistical account of fiction also) more on the stored the relationship between stimulus past than on the present. On this (input) and behaviour (output) in view all perceptions are essentially animals and men. An engineer fictions: fictions based on past would go on to suggest “models”, experience selected by present of what the internal mechanisms sensory data. Here we should not might be which transform inputs equate "fiction" with "false". Even into the outputs. But, rather the most fanciful fiction as written curiously. Skinner does not is very largely true. or we would attempt to make this further step, not understand it. Fictional and apparently distrusts it. He says characters in novels generally have remarkably little about brains, and the right number of heads, noses at times denies memory and indeed and even many of the opinions of all internal processes. His people we know. Science fiction description is purely in terms of characters may have green hair and input output relations, with an exoskeleton-but is this novelty emphasis on how the probability of not a mere reshuffling of the pack certain kinds of behaviour is of our experiences? It is doubtful changed by environmental- if a new "card”, suddenly changes, especially "reinforcers". introduced could be meaningfully described or seen. Skinner himself has little interest specifically in perception, The passive paradigm may, at but passive theories of perception least initially, seem more are in many ways similar. They Times Literary Supplement JUNE 23, 1972 3 have the same initial scientific quite long gaps in sensory data, credibility, but are (I believe) and remain appropriate though essentially incorrect. They deny there is no sensory input. But how that perception is an active can "output" be controlled by combining of features stored from “input” when there is no input? the past, building and selecting The fact is that sensory inputs are hypotheses of what is indicated by not continuously required or sensory data. On the active available, and so we cannot be account we regard perceptions as dealing with a pure input-output essentially fictional. Though system. Further, when we consider generally predictive, and so any common action, such as essentially correct, cognitive placing a book on a table (a fictions may be wrong to drive us favourite example of philosophers) into error. On this active view, we cannot test from retinal images both veridical (correct-predictive) the table's solidity and general and illusory (false-predictive) book-supporting capabilities. In perceptions are equally fictions. To engineering terminology, we perceive is to read the present in cannot monitor directly the most terms of the past to predict and important characteristics of objects control the future. This account is which must be known for very different from the passive behaviour to be appropriate. This story implied by Skinner's implies that these characteristics behaviourism, and most ably are inferred, from the past. The propounded by James J. Gibson other highly suggestive-indeed and Eleanor Gibson (whose article dominating -- fact is that is on page 711). perception is predictive. In skills, there may be zero delay between Why should one want to push sensory input and behaviour. But all this stuff about " brain fictions" how could there be zero delay, (as I do) when stimuli and except by acting upon a predictive responses are so easily observed, hypothesis ? (Surely J. J. Gibson's and so like the usual stuff of description of perceptions as science? The essential reason is (I selections from the available believe) very easily demonstrated, "ambient array" will not do : it by common observation and by would have to be a selection from experiment. Current sensory data a future "ambient array" for the (or stimuli) are simply not passive account to work : but this adequate directly to control evokes a metaphysics we cannot behaviour in familiar situations. welcome. The significance of Behaviour may continue through prediction in perception has been Times Literary Supplement JUNE 23, 1972 4 for too long almost totally operations serially) that the ignored.) computer requires a vast amount of stored data of common object It is the fact that behaviour does properties with ready and rapid not need continuous, directly access. It requires, in short, what appropriate sensorv data that we have called “fictions” to forces upon us the notion of augment and make use of data inference from available sensory monitored from the world by its and brain-stored data. This camera eye, and – in machines account is very much in the dealing with real objects – its tradition of the polymath touch probes. In short: we may nineteenth – century physicist and think of perception as an physiologist, Hermann von engineering problem, but it is a Helmholtz, who described highly atypical problem even for perceptions as “unconscious advanced computer engineering,m inferences”. This notion was and it requires a special philosophy unpalatable to later generations of which is unfamiliar in science, psychologists, who were over – because only brains and to a influenced by philosophers in their limited extent computers are role – sometimes useful, but in this cognitive. case disastrous – of guardians of semantic inertia: objecting to The notion that interpreting inference without consciousness. objects from patterns is a “passive” But with further data on animal business must strike the computer perception, and computers capable programmer engaged on this of inference, this essentially problem, in Machine Intelligence, semantic inhibition has gone. as an extremely unfunny joke. His Curiously, though, the kinds of problem is to devise active inference required for perception programs adequate even for are remarkably difficult to perceptual problems solved by compute. simple creatures long before man came on the scene. The recent engineering – science of Machine Intelligence is The notion of perceptions as finding heavy weather designing predictive hypotheses going computer programs to identify beyond available data is alien and objects from television camera suspect to many physiologists. pictures. The reason seems to be Cognitive concepts appear (apart