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We present subarcminute-resolution (B10A), highÈdynamic range radio observations of TychoÏs supernova remnant (3C 10) at j \ 20 cm and j \ 90 cm with the Very Large Array (VLA). The thermal-noiseÈlimited 90 cm image has been compensated properly for the noncoplanar characteristics of the VLA and is the most sensitive low-frequency image of this source presently available. We use these images to search for spatial variations in the continuum radio spectral index within the remnant. Such spatial variations should be related to the electron acceleration processes associated with the evolution of the blast wave. We have also utilized, for the Ðrst time in an analysis of a supernova remnant, spectral tomography to search for localized regions within which the spectral index is di †erent from the surroundings. We have identiÐed 13 Ðlaments, ranging in size from B40A to B260A, embedded in a smoother, background component. The average spectral index of the Ðlaments (SaT \ [0.52^0.02) is consistent with that of the background component (SaT \ [0.500^0.007). However, the Ðlaments in the outer rim show a trend such that brighter Ðlaments have a Ñatter spectral index. This trend may be due to either supernova remnant (SNR) blast waveÈambient medium interactions or internal inhomogeneities of the magnetic Ðeld within the remnant. These hypotheses could be tested by an image at comparable resolution and Ðdelity at a third frequency.

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This paper describes data which for the first time show correlations between the visual steady state evoked response (SSER) and human cognitive activity. Individual subjects exhibit characteristic evoked potential phase relationships to flicker stimuli, and these were found to be related to the individual's speed of response in a memory scanning task. In addition, evoked response phase lags to different flicker frequencies were related to the component processes involved in the task. The brain's response to high frequency flicker is related to the sensory input portion of a memory scanning task while the response to medium frequency flicker is related to the memory look‐up aspects of this task.

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