The human auditory system is exceptional at comprehending an individual speaker even in complex acoustic environments. Because the inner ear, or cochlea, possesses an active mechanism that can be controlled by subsequent neural processing centers through descending nerve fibers, it may already contribute to speech processing. The cochlear activity can be assessed by recording otoacoustic emissions (OAEs), but employing these emissions to assess speech processing in the cochlea is obstructed by the complexity of natural speech. Here we develop a novel methodology to measure otoacoustic emissions that are related to the time-varying harmonic structure of speech (speech-DPOAEs). We then employ the method to investigate the effect of selective attention on the speech-DPOAEs. We provide tentative evidence that the speech-DPOAEs are larger when the corresponding speech signal is attended than when it is ignored. Our development of speech-DPOAEs opens up a path to further investigations of the contribution of the cochlea to the processing of complex realworld signals.

A cusptron device operating at sixteenth cyclotron harmonic has been set up for the development of a compact and high power microwave source. An axisencircling electron beam of 22Kev (7= 1.044) as the radiation source is produced from an annular thermionic cathode of 1.4 cm radius and 0.16 cm radial thickness with a pierce -type focusing electrode together with a cusp magnetic field.A 16-slotted waveguide with b/a =1.23 is used for the 2r mode operation where b and a are the radii of the slots and the inner wall of the waveguide respectively. a =1.7 cm is designed so that the operating magnetic field is 364 Gauss and the radiation frequency is 15.6GHz. 11% efficiency is achieved from particle simulation. The results of our experimental study will be presented and a comparison of the experimental results with those of particle simulation will be made.

Through the use of a computer particle simulation, a study of the operational characteristics of an eighth harmonic cusptron device is presented. The functional dependence of the saturation efficiency upon (1) the beam energy and (2) the ratio of the outer and inner radii of the slotted waveguide is determined for both the π mode and 2π mode. The results show that the π mode has a better conversion efficiency than the 2π mode.

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