Neural Processing of Complex Electric and Acoustic Stimuli

One aspect of deafness, the loss of sound awareness, is largely alleviated by cochlear implants now available if sufficient primary afferents survive. However, the loss of speech discrimination ability, which is of greater functional importance for integrating the patient into a “hearing” world, has not been satisfactorily resolved by current prosthetic designs. This chapter examines two classes of neurophysiological mechanisms on which successful encoding of speech and other complex sounds as acoustic or electrical stimuli depend: the peripheral transduction process and central processing. Acoustic and electrical transduction are inherently different, but each is selective in the stimulus information it passes. They can be compared when both are treated in equivalent stimulus terms. Central processing mechanisms accept and act on acoustic input much more readily than electrical input for reasons which are only partially known. We contrast the processing of electrical and acoustic inputs for comparable stimulus parameters and suggest ways to enhance or replace the processing now available with implants.