Induction of visual imagery during NREM sleep

In an attempt to induce eye movements (EMs) in non-rapid eye movement sleep, light and sound stimuli were presented to human subjects (at below-waking threshold) during stage 2 sleep. EMs were used as an indicator of ponto-geniculo-occipital (PGO) wave activity. When at least one concurrent EM in response to the stimuli was observed, the subjects were awakened and mentation reports collected. Compared to equivalent control periods with no stimulation, awakenings from the stage 2 stimulation condition showed a higher frequency of visual imagery reports, electroencephalogram alpha activity, and k-complexes. Additional control and stimulation conditions elicited from rapid eye movement sleep awakenings showed no significant differences in the frequency of visual imagery reports. When the amount of alpha activity before stage 2 awakenings from which imagery was reported was compared to that from which imagery was not reported, imagery awakenings showed significantly more alpha. Results can be interpreted as evidence for a link between PGO activity and dreaming in humans or in terms of an arousal-window hypothesis of visual hallucinations.     

Optical fibre diameter variations and their effect on backscatter loss measurements

Diameter variations in optical fibres are shown to affect back-scatter loss measurements by a mechanism which primarily involves attenuation of the backward travelling light. A simple model which predicts anticorrelated loss features when measured from opposite ends of the fibre is verified experimentally.     

High-resolution measurement of diameter variations in optical fibres by the backscatter method

The backscatter signal measured with high resolution from optical fibres with complex diameter variations is shown to follow precisely the diameter profile. The local attenuation which is anticorrelated from opposite ends of the fibre is compared with a simple theoretical model.     

Spectral- and length-dependent losses in optical fibres investigated by a two-channel backscatter technique

Spectral- and length-dependent losses in optical fibres have been investigated using a two-channel technique for back-scatter-waveform analysis. Results are compared with measurements obtained by the `cutback? method over the wavelength range 0.82?1.07 ?m. Attenuation measurements at 0.95 ?m show a significant variation in OH- concentration along the fibre.