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We investigated whether pitch-synchronous neural activity could be recorded in humans, with a natural vowel and a vowel in which the fundamental frequency was suppressed. Small variations of speech periodicity were detected in the evoked responses using a fine structure spectrograph (FSS). A significant response (P [much less than] 0.001) was measured in all seven normal subjects even when the fundamental frequency was suppressed, and it very accurately tracked the acoustic pitch contour (normalized mean absolute error < 0.57%). Small variations in speech periodicity, which humans can detect, are therefore available to the perceptual system as pitch-synchronous neural firing. These findings suggest that the measurement of pitch-evoked responses may be a viable tool for objective speech audiometry. Index Terms--Bioelectric potentials, biomedical signal processing, speech processing, time-frequency analysis.

Researchers have investigated the impact of congestive heart failure (CHF) on the rhythmic control of muscle sympathetic nerve activity (MSNA). This involved characterizing oscillations in MSNA in the frequency domain in health men and men with CHF. These were related to blood pressure (BP), breathing frequency and heart rate (HR). It was possible to identify spectral power in the MSNA signal which is similar in magnitude in people with normal and impaired ventricular functions in relation to total power and the relative proportion of harmonic and nonharmonic elements.

We propose the binaural auditory system as a candidate neural system that may be disrupted by exposure to relatively weak LF magnetic fields. Extracellular currents, induced by time-varying magnetic fields, may change the timing of action potentials in the auditory nerve, thereby disrupting sound localization when interaural time differences are very small. Three subjects were exposed to a 1000 Hz magnetic field--with a maximum rate of change of 2.3 T/s at the location of the cochlea--while presenting two identical 1000 Hz tones randomly delayed to the left or right ear by less than 10 ps. The subjects were asked whether the signal was perceived to be displaced to the left or right side of midline. After a total of over 20,000 trials, conducted at different phase angles between the field signal and the tones, there was no clear evidence for a consistent change in performance when the magnetic field was present. This, however, does not rule out an effect at other combinations of magnetic and acoustic frequencies.