CONDITIONS FOR VERSATILE LEARNING , HELMHOLTZ ’ S UNCONSCIOUS INFERENCE , AND THE TASK OF PERCEPTION

It is a mistake to consider perception and learning separately because what one learns is strongly constrained by what one perceives, and what one perceives depends on what one bas experienced. I shall propose the hypothesis that perception is the computation of a representation that enables us to make reliable and versatile inferences about associations occurring in the world around us-that is, perception pmpares the ground for learning. The statistical problem in learning is to determine whether a compound event such as “C followed by u” is a random co-occurrence or a significant association, for if it is the former it would bea mistake to pay any particular attention to C. whereas ifit is the latter C is a conditional stimulus for U and a useful predictor for it. Now you cannot decide whether the association is random or not without knowledge of the prior probabilities of C and U: hence on my hypotbeais when you perceive an object or event the representation must not only signal “it’s there” or “it’s happened”, but must also make evident (or rapidly accessible) the prior probability of what has been signalled. Furthermore it must do this for all the objects or events that can act as conditional stimuli, and this implies that the representative elements should be statistically independent (or approximately so) in the normal enviromnent. Forms of coding that would do this, and the relationship with Helmholtx’s unconsicous inference, will be discussed. These considerations imply that the task performed in perception has been overlooked both by learning theorists and by connectionists working on associative and adaptive networks. Coding for independence may be particularly important in understanding the developmental process during the sensitive period: it may be the operation that leads ontogenetically-timed, activity-dependent, connections to imprint appropriate codes if the animal has experience, but inappropriate codes without experience. Coding Conditioning Cortex Representation Sensitive period Inference Hehnholtx Prior probability Perception THE RELATION OF PERCEPTION TO LEARNING I decided to talk on this topic with some trepidation because Gerald know8 his Helmholtz so much better than I do and does not, I suspect, trust a non-German speaker to get him right. However Helmholtz expressed himself with unrivalled clarity and the ideas I shall propose are directly descended from his well-argued proposal that percepts represent unconscious inferences, so I cannot avoid bringing him in and must risk Gerald’s criticisms. My argument is, briefly, that to understand perception one must view it as a prologue to learning. Acquiring new knowledge of the world is among the most important things our brains do for us, and for most people at this meeting it is probably the most interesting thing it does. So I shall try out on you the idea that perception is the process of preparing a representation of the current sensory scene in a form that enables subsequent learning mechanisms to be versatile and reliable. I shall assume that learning is based on what we perceive, and that cerebral cortex is where the representation we perceive is computed, even though neither assumption is 100% certain McCormick, Lavond, Clark, Kettner, Rising and Thompson (198 1) and Yeo, Hardiman and Glickstein (1985) have shown that conditioning of the nictitating membrane response in the rabbit occurs in the cerebellum, and I am sure that many other forms of learning can occur without the learner consciously perceiving the sensory stimulus that is learnt. Nevertheless our perceptions certainly provide much of the information from which we learn and the cerebral cortex must create the representations used for this purpose. This is a sufficient basis for my argument, though one should be aware that other types of representation and learning do occur.