["Demultiplicated" neuromal dischare periodicities correlated with stimulus frequency in colliculus inferior and geniculatum mediale]

[The phenomenon of hearing: an interdisciplinary discussion. II]

This part of the paper deals with the neurophysiological background of speech analysis and hearing of music. Single vowel- and consonant-detector cells could be clearly separated at the colliculus and geniculate level (Kallert, Keidel). Musical stimulation is decoded at three levels: hair cells, geniculate, and auditory cortex. Human cortical evoked potentials represent rhythm, consonance, and (as DC-shift) the emotional content of music. Marked harmonics, even of single hair-cell vibrations and in single units of medial geniculate in combination with clock-cell networks, are the physiological basis of "harmony" in music. Dissonant stimuli are detectable at the cortical level in man (Finkenzeller, Keidel).

[The phenomenon of hearing: an interdisciplinary discourse. I]

For the last century hearing has been considered a purely passive process. G. S. Ohm's and H. v. Helmholtz's resonance theory of hearing was widely accepted until Wien's fundamental objection led to G. v. Békésy's and O. F. Ranke's travelling wave theory, the hydrodynamics of the inner ear that distributes the frequencies along the basilar membrane, which acts as the "first filter". Seebeck, Licklider, Schouten, and deBoer emphasized also the time domain and developed the concept of periodicity hearing and the "residue phenomenon". However, it was not until the concept of the "cochlear amplifier" and "active hearing" with energy generation during the transduction process within the ear itself was introduced that the "second filter" could be understood. Kemp's echo was the key to this revolutionary step in the theory of hearing.

Neurophysiological requirements for implanted cochlear prostheses

In a few introductory remarks the technological, neurophysiological and clinical assessments of new developments in modern, highly sophisticated hearing aids are reviewed. The necessity of preprocessing auditory information is discussed as well as the problems related to the choice of suitable electrodes, and, in particular, how much auditory information for speech communication, given by the product of number of just noticeable differences in intensity, number of just noticeable differences in frequency, number of channels for conveying neurophysiologically processable signals would be required as a minimum for cochlear implants to enable patients to communicate with one another. Finally, the fact that a number of different sensory modalities converge in to man's cortical association area might possibly be used for some special application of a multimodal input in a completely deaf patient with the aim of enabling him to understand human speech.