Auditory Coding in Higher Centers of the CNS

Les E. Atlas Department of Electrical Engineering nucleus. In particular, some strong correlation between University of Washington single-unit electrical activity and the actual shape and structure of the nerve cells has been found [7-81. THE PERCEPTION OF SOUND is actually a multifaceted The dorsal cochlear nucleus is not as well understood and I task; frequency discrimination, loudness judgment, sound probably more complicated than the ventral cochlear nucleus. localization, and speech perception place different demands Anatomical and response-type classifications indicate that, on the auditory system. Since the human auditory system can while the input channels to the dorsal and ventral cochlear have the ability to perform all of these tasks, a very diverse nuclei are the same, the shape and structure of the cells in the set of neural structures is likely. This paper will avoid the two regions are quite different [9]. Also, the dorsal region almost impossible complexity of unifying all functions of provides a greater number of inhibitory single-unit responses sound perception by independently describing some higher than does the ventral region [10]. level coding aspects of frequency discrimination, amplitude As the auditory pathway is ascended, neural crossings to representation, and speech representation. The bulk of the the contralateral side become dominant. Some of the second information that will follow is based on a grouping of other order neurons within the cochlear nucleus give off axons researchers' published results. which cross over via the trapezoid body and terminate at This paper has two goals; the first is to consider the synapses in the superior olivary complex. Other dorsal cells feasibility of electrical implants for the profoundly deaf, at run directly to the contralateral superior olivary complex, and levels higher than the cochlea or auditory nerve, for forms of a few ventral cochlear nucleus cells remain on the ipsilateral deafness where the auditory nerve is non-functional or nonside. It seems possible that this partitioning of contralateral existent. An understanding of anatomical and functional and ipsilateral axons from the ventral cochlear nucleus is attributes of higher auditory centers is needed to address this related to binaural tasks. However, as will be discussed problem. The second goal is to consider these higher centers below, this is not the only place where significant cross-over as very advanced and efficient speech processing structures. occurs. If the code and architecture of these neural structures were understood, improvements to speech recognition and processing algorithms could be developed by mimicking certain aspects of human auditory processing.