Most studies in auditory neurophysiology have utilized tonal stimuli to determine the coding properties of neurons in the cochlear nuclei. In this investigation of the kangaroo rat, cochlear nuclei, neuronal responses to vowel sounds, as well as tones, were studied. The vowel sounds, each about 40 msec in duration were: see article. Five were linked together to form a 200 msec stimulus and various combinations of five vowel sounds provided us with 18 different stimuli. The results show that neurons in the cochlear nuclei are remarkably sensitive and selective to vowel sounds. Furthermore, the responses of these neurons to pure tones do not provide a complete basis to predict the types of responses to the vowel sounds. More significant is the finding that the neural discharge rate and pattern of discharge to a particular vowel may depend on where the vowel appears in the stimulus and what other vowel precedes it. This vowel positional effect is not the same for every neuron. We have called this phenomenon a neural "set".

Acoustic Stimulation↗

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Central auditory fatigue.

The results of this study, based on evoked responses and single-neuronal responses, reveal that there is a central involvement in auditory fatigue. In these experiments, cochlear potentials (microphonic and whole-nerve action potential) and inferior colliculus electrical responses were simultaneously obtained before and after excessive sound exposure. In general, sound exposure produced a greater reduction of the collicular evoked responses than of the cochlear microphonics and action potentials. Recordings from single neurons support the evoked-response findings.

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Early tone-evoked responses in normal and hearing-impaired subjects.

Early evoked responses to 500-Hz tone bursts were recorded from normal and hearing-impaired children and adults. The threshold values of the early evoked responses provide useful estimates of auditory functioning, even among difficult-to-test populations, such as deaf-blind children. Latency measures indicate that the early response is generated at the brain stem. Latency measures from hearing-impaired subjects show that the response can identify recruitment. Several subjects having a history of nonspecific communication disorders, e.g., dyslexia, exhibited aberrant early evoked response waveforms. The early-evoked response measures, therefore, amy be useful in detecting and assessing communication disorders which are believed to be of cortical origin, but now should be considered to have a basis in brain stem dysfunction.

Acoustic Stimulation↗