Perspectives in Biology and Medicine

EMERGING PRINCIPLES OF SENSORY CODING WILUAM R. UTTAL* Determination ofthe relationship between afferent neural message pattern and perceived experience has become one of the major problem areas in psychobiology. A wide variety ofdifferent kinds ofstudies can be classified under the general rubric of "neural coding" or, more dramatically , "breaking the neural code." In all ofthese experiments the central problem is to discover how specific characteristics ofthe sensory experience are represented by the possible parameters ofvariation ofthe nervous signals. The recent upsurge in interest and progress in this field is based upon foundations of biological simplicity and technological innovation. Sensory structures and functions are all simpler, better ordered, and more easily understood than the function and structure of the higher mental processes. Yet, like the model preparations studied in lower animals, the study ofthe sensory mechanisms can also contribute to our understanding ofneural representation in a more general way. New psychophysical techniques, new electrophysiological techniques, and new computer control and analysis techniques have all added impetus to the study ofthis set ofproblems. Certain problems ofsensory coding, under attack with the aid ofthese new methods, have proven susceptible to experimental investigation in a way which cannot be matched in the much more refractory problems of the neural basis of higher cognitive activities. The amount ofresearch data which has emerged from various laboratories in the last ten or twenty years has been massive and, compared to central neural studies, quite unequivocal. Nevertheless, there have been few attempts to consider some ofthe basic biological generalities of which each experimental result is but one exemplar. In the light of this * Laboratory ofSensory Sciences, University ofHawaii. On leave from the University ofMichigan . Address reprint requests to 1042 MHRI, University ofMichigan, Ann Arbor, Michigan 48104. 344 William R. Uttal · Sensory Ctding Perspectives in Biology and Medicine · Spring 1969 new data, it appears that some of our previously accepted notions of sensory information transmission and processing are undergoing modifications or reinterpretation. Subtle and delicate changes in our perspectives are occurring which often go almost unnoticed until they become entrenched in our scientific culture and must be transmitted to a new generation. In general, science is a conservative process, changing its formal axioms only when the data and/or clamor becomes overwhelming. The necessity for this conservatism is obvious, but there is another aspect ofthe importance ofour basic assumptions which also must be considered. Our axioms and assumptions as well as our experimental technology color the way in which we look at the data obtained from a given experiment. We tend to see what is generally consistent with our previous assumptions, and we generally tend to perpetuate established points of view. Very often a simple restatement ofan axiom can change an entire experimentaltheoretical edifice. It is for this reason that it is important that occasionally we look beyond the measuring instruments of our laboratory to the premises on which we base our observations. It is the purpose ofthis paper to overtly consider some ofthese changes by reviewing some ofthis new evidence and to call attention to the gradual metamorphosis ofour classical views, which is occurring under the pressure of this new data. This is not a completely novel effort. Many scientists have individually come to some ofthe same conclusions presented in this paper. In this current effort, though, a number ofthe currently emerging principles are collected together in a way which emphasizes the principles themselves rather than embedding them within the context of a single specific experiment. It should also be noted that many ofthe points which we make have already been made years ago by other writers. It is possible that almost any ofthese points could find an antecedent in history, so no claim to originality is intended. Wherever possible, an effort has been made to acknowledge those who have earlier made these points. The reader's attention is especially directed to the report made by MacKay [i] on a symposium on neural communication sponsored by the International Brain Research Organization. Some ofthe points made here were apparently also topics ofdiscussion at that meeting. Before we begin the main text of this discussion, it may be well to make a few specific definitions to clarify our usage of...