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OUR AUDITORY WORLD is an'.V, amazingly complcx scrics of con-centric spheres. The head occupies the center and seems, for the most part, to be stationary while sound emit-ters shift and recede and crisscross i * around us (Fig. 1). The problem of _k i how to locate and track a single mov-ing sound source, or even several simul-taneous sound sources, has been met

and solved hy naturę in a variety of ways. The insect, the bat, the porpoise, and man have each worked out spe-cial compromises—some morę success-ful than others.

The chief function of the ears of primitive vertebrates w*.s certainly direction-finding. To promote this function the ear’s frequency sensitivity had to go far beyond the low-frequency hearing of reptiles, and evolve "direc-tional antennas" and the muscles for

• ABOUT THF AUTHOR

DR. HARRIS receiv*d his Ph.D. in physio'o9 ical psychology from tf»e Universfty n£»P«r^k ester in 1942. Since 1943 h headed the Auditory Research 8ranch of the U. S. Naval Medisal Res/arch LaToratory. He is co founo'. r and director of research of the C. W ShilCng Auditory Research Cejjter. Inc. of ^ruton, Conn., a priyate non-protit organiia-•ion devoted to scholarship and Research in

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eye, at least in the primate, evolved simultaneously into an instrument with ,.an elaborate oculo-motor system for Jtarget tracking. We thus have, in the ' human, the equivalent of an omni-dircctional search radar (the ear) and the extremely directional fire-control radar (the eye). See Fig. 2.

Once our ears have put our eyes "on target” they can pretty well be dispensed with and, in fact, the high-frequency-range capabilities and the large mobile outer ear parts of the lower animals are disappearing rather rapidly—as such things go. We no longer boast the exquisite hearing in the higher octaves—enjoyed by the dog and the cat—nor are we independent of our eyes for ordinary locomotion.

Despite these evolutionary changes, a great deal of "liveness” and three-dimensionality exist in our auditory