Data on time response in the nervous system are available for animals. Rate-matching data for humam ,,ubject,, with implanted electrodes are available. These data do not tell us with certainty up to what rate people with normal hearing utilize time information directly. In many experiments an attempt to measure time re,,ponse is confused by the presence of spectral clues. Short-term spectral clues exist in stochastic •,½qu½.cc•, of positive and negative pulses and in modulated white noise, both of which have a white longterm •,p½ctrum. These clues are periodicity (with a period equal to the pulse or modulation rate) and •,ymmctry (about frequencies equal to integer multiples of half this rate), differences at different frequencies in' the peak-or rrns-voltage distribution function of the output of a narrow-band filter and, in the case of ,,rochaslit pulse sequences, differences in extreme intensity at different frequencies. It may be that the ability to match at high rates and the perception of tonal quality that subjects with excellent and trained hcari.g, such a•, musicians, exhibit for white-spectrum stochastic pulse sequences or gated noise is due to the re•,idue phenomenon or to spectral clues discussed in this paper. I'ACS numbers' 43.66.Mk, 43.66.Ba, 43.66.Lj INTRODUCTION In animal hearing direct measurements can be made of the firing of neurons in response to sine waves or pulse trains of various frequencies or rates. Histograms of firings show that statistical synchrony of firings with stimuli is preserved in the eighth nerve up to stimulus frequencies of about 4000-5000 Hz (Rupert, Moushegian, and Galambos, 1963; Peake, Kiang, and Goldstein, 1962; Rose etal., 1967). However, it is not clear up to what repetition rate animals make any use of time information. 1 Neurophysiological data on synchrony in firing are not available for human beings. However, electrodes have been implanted in totally deaf patients who exhibit function of the eighth nerve. These give a partial restoration of hearing through electrical stimulation. In such subjects, all neurons are stimulated by the same signal and any ability to distinguish among stimuli must be based on time information.Tests on a patient with six electrodes permanently implanted in the modiolus portion of the eighth nerve by F. Blair Simmons in 1964 showed an ability to discriminate pulse rates up to 300 pulses per second and an ability to discriminate two short pulses from a single pulse when the interval was increased and when the pulses were separated by more than 5 msec. (Simmons etal. , 1965.) Michelson and his associates have reported on the responses of four patients implanted with intracochlear stimulating electrodes. Prior to implant, the hearing of the ear later implanted had deteriorated to total deafness in three of the patients; in the other, the implanted ear had been deaf from birth (Michelson, 1971). The apparent pitch reported by three subjects rose steadily with increasing frequency to about 500 Hz. At higher frequencies the "tones" heard ...
In this paper, we present the architecture and design of the Aquarius instrument: a spaceborne combination radiometerscatterometer in L-band, for measuring ocean surface salinity. In order to achieve the unprecedented measurement stability of 0.1 Kelvin for the radiometer, the Scatterometer (for correction of the sea surface roughness) is required to have a calibrated stability of 0.1 dB. Active and passive thermal control was utilized as well as RF self calibration. Novel test techniques were also developed to verify the stability requirement was met.
Responses to acoustic stimuli which differ in both spectrum and time structure may depend on both the time and the place mechanisms of hearing. Green [D.M. Green, “Temporal acuity as a function of frequency,” J. Acoust. Soc. Am. 54, 373–379 (1973)] has used short stimuli which differ in time structure only. Here we describe and analyze two sorts of white-spectrum stimuli with a periodic time structure. These are stochastic sequences of positive and negative short pulses of equal shapes and areas, and white noise multiplied by a periodic signal. While such stimuli have a white power spectrum, the short-term power spectrum exhibits periodicity and symmetry. The energy distribution function of the short-term power spectrum can differ for different frequencies. The time structure can be obliterated without changing the spectrum, and the spectrum can be changed without obliterating the time structure. [Work supported by Bell Telephone Laboratories and Xerox Corporation.]
The upcoming Aquarius sea-surface salinity mission has tight requirements on backscatter measurement accuracy and stability at L-band frequencies (1.26 GHz). These requirements have driven the development of new capabilities in the scatterometer's backend detector electronics, which are the focus of this paper. Topics include the development of flight-grade hardware aboard the scatterometer for radio frequency interference (RFI) detection and mitigation, and analog/digital electronics design techniques used to reduce system noise and achieve highly linear power detection over a wide dynamic range. We also summarize the approach taken to test the scatterometer's processing and control functions at the level of the integrated Aquarius flight instrument, and present some recent results from the integrated testing campaign.
The upcoming Aquarius sea-surface salinity mission has tight requirements on backscatter measurement accuracy and stability at L-band frequencies (1.26 GHz). These requirements have driven the development of new capabilities in the radar's backend detector electronics, which are the focus of this paper. Topics include the development of flight-grade hardware aboard the scatterometer for radio frequency interference (RFI) detection and mitigation, and analog/digital electronics design techniques that reduce system noise and yield highly linear power detection over a wide dynamic range. We also summarize the approach taken to test the scatterometer's processing and control functions at the level of the integrated Aquarius flight instrument, and present some recent results from the integrated testing campaign.
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