auditory cortex, presented by Reale and Imig in 1980. The description of the structure and function of the lower and upper auditory brain stem has been adjusted to agree with the modern view as presented by Lindsay Aitkin in his important monograph, The Auditory Midbrain.3
First, a brief overall description of the main stations between the cochlea of the inner ear and the auditory projection areas of the cortex. We follow the pathways drawn in Figure 1.
There is general agreement today that the initial, still mechanical, frequency analysis of a pure or complex tone is completed at the level of the basilar membrane; the complex tone is resolved in its components in a process equivalent to a Fourier analysis, the result of which is communicated to the auditory relays of the brain. The change to an electric-chemical analysis occurs in the sensory cells of the membrane, where the information is transmitted to the nerve fibers leading from the peripheral part of the system into the central nervous system (CNS). A remarkable observation is that the main nervous pathways of a species develop at their embryological level only under a very weak external influence. The process of maturing of the visual as well as the auditory centers precedes that of the peripheral receptors.4 We will return to this observation, which is vital to the understanding of the conditions for learning, when discussing pitch perception.
The first station in the CNS after the auditory nerve is the nuclei cochlearis (CN) in the hindbrain. The projection of the CN is tonotopically organized. These cell groups possess various kinds of neurons situated in different parts of the nuclei. Some respond only, or preferably, to low and middle frequencies, others to high frequencies; some neurones specialize in reproducing repetitive____________________