Plans for phase coherent long baseline interferometry for geophysical applications using the Anik-B communications satellite

A pilot project to establish an operational phase stable very long baseline interferometer (VLBI) for geophysical studies is described. Methods for implementation as well as practical applications are presented

The effect of long-term unilateral deafness on the activation pattern in the auditory cortices of French-native speakers: influence of deafness side

<p>Abstract</p> <p>Background</p> <p>In normal-hearing subjects, monaural stimulation produces a normal pattern of asynchrony and asymmetry over the auditory cortices in favour of the contralateral temporal lobe. While late onset unilateral deafness has been reported to change this pattern, the exact influence of the side of deafness on central auditory plasticity still remains unclear. The present study aimed at assessing whether left-sided and right-sided deafness had differential effects on the characteristics of neurophysiological responses over auditory areas. Eighteen unilaterally deaf and 16 normal hearing right-handed subjects participated. All unilaterally deaf subjects had post-lingual deafness. Long latency auditory evoked potentials (late-AEPs) were elicited by two types of stimuli, non-speech (1 kHz tone-burst) and speech-sounds (voiceless syllable/pa/) delivered to the intact ear at 50 dB SL. The latencies and amplitudes of the early exogenous components (N100 and P150) were measured using temporal scalp electrodes.</p> <p>Results</p> <p>Subjects with left-sided deafness showed major neurophysiological changes, in the form of a more symmetrical activation pattern over auditory areas in response to non-speech sound and even a significant reversal of the activation pattern in favour of the cortex ipsilateral to the stimulation in response to speech sound. This was observed not only for AEP amplitudes but also for AEP time course. In contrast, no significant changes were reported for late-AEP responses in subjects with right-sided deafness.</p> <p>Conclusion</p> <p>The results show that cortical reorganization induced by unilateral deafness mainly occurs in subjects with left-sided deafness. This suggests that anatomical and functional plastic changes are more likely to occur in the right than in the left auditory cortex. The possible perceptual correlates of such neurophysiological changes are discussed.</p

Response properties of neurons in the inferior colliculus of the guinea-pig.

Single unit responses to tone pips (200 ms duration) or clicks were studied in the inferior colliculus of anaesthetized guinea-pigs. In all, 360 neurons were investigated. The tonotopic organization of neurons in the inferior colliculus and shapes of the threshold tuning curves were comparable with the data known in other laboratory animals. The majority of neurons (83.5 percent) displayed a tonic response to tonal stimuli, the remaining 16.5 percent of units responded with a typical "on" reaction at the beginning of the stimulus. The spike-intensity functions of 50 percent of neurons were of the non-monotonic type, the saturation of response was observed usually at 20-30 dB above the threshold. Monaural stimulation of the contralateral ear evoked an excitatory response in all cases; ipsilateral ear stimulation exerted an excitatory response in 61.8 percent of neurons, an inhibitory response in 17.6 percent of neurons and for 20.6 percent of units ipsilateral ear stimulation was uneffective. The occurrence of neuronal responses to stimuli with an interaural time delay or intensity differences was also investigated