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Biomedical subjects

W D Keidel

Publications and source records attributed to W D Keidel.

18 recordsLinked to original sources
PubMed1992

[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.

Auditory Perception↗
PubMed1992

[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).

Auditory Cortex↗
PubMed1989

The computer-vibromyography as a biometric progress in studying muscle function.

Muscular vibrations were recorded from different relaxed and contracted skeletal muscles in human subjects, with the use of a piezo-electric device. Simultaneous wire-EMG recordings were performed. Spectral analysis of the acceleration curves (vibromyograms) disclosed muscle and function dependent compound frequency patterns. We suggest that the activity of motor units including the action of central reflex loops and oscillatory driving is mainly responsible for the muscular vibrations. Other sources are discussed. Computer-Vibromyography as a mechanical ensemble measurement supplements bioelectric EMG techniques and classical tremor analysis and provides further insights into the function of muscle and motor-system.

Adult↗
PubMed1976

[The significance of the CNS for the physiology of hearing (author's transl)].

Some general aspects of auditory perception (funnelling, contrast, pattern recognition, form perception, methodological limitations) are discussed in the first part of this presentation. The modern concept of the hydrodynamics of the inner ear, including electronic modelling of the function of the basilar membrane is their dealth with. For the encoding and decoding processes of the auditory system the different grades of intensity function at the different neuronal levels is compared with that of the envelope of the basilar membranes deflection. The influence of the efferent system is discussed. In a third section of the paper some new results from our department are reported concerning the single unit activity at geniculate level recorded from the awake cat by means of a telemetric system. Neurophysiological correlates to vowel- and consonant detectors and their relations to be the phonem recognition of speech could be demonstrated. Finally, the most recent state of objective audiometry is discussed (DC-potentials, simultaneous records of electrocochleogram and cortically evoked activity, relations to EEG's power spectrum, and brains changes in vigilance) with a view of future approaches to ERA.

Animals↗
PubMedDate not supplied

Neurophysiological requirements for implanted cochlear prostheses.

Regarding the neurophysiological requirements for implanted cochlear prostheses, we have discussed (i) the complexity of speech sounds, (ii) problems of intensity, then (iii) the frequency problem, and (iv) finally the possibility of a frequency transposition to the genuine frequency range of a single fibre of any mechanoreceptor and its connecting nerve fibre (less than 1 kHz) for the construction of an intracochlear prosthesis. In general it would seem necessary to seek compromises based on the fact that speech, at least the vowels, contains redundancy and that the use of additional sensory channels might be helpful for cochlear implants. Certainly besides other preprocessing techniques for speech information, the multichannel stimulation set-up of special electrodes has to be used to convey a sufficient amount of speech information to restore the faculty of speech perception in completely deaf patients. Decompression of intensity range and compression of frequency range might be especially useful.

Acoustic Stimulation↗