Jacques Carmeliet

The system bandpass required to avoid distortion of early components when averaging somatosensory evoked potentials

Abstract The effects of 14 filter conditions with cutoff ranging from 3 kc/sec to 50 c/sec and with either 6 or 24 dB/octave roll off were studied when averaging the somatosensory cerebral potentials evoked by electrical stimulation of fingers in normal adult men. Severe distortions of latencies and voltages were observed for low pass filtering below 1 kc/sec. It is emphasized that the overall system bandpass should extend to 3 kc/sec when studying the early components and when estimating the onset latency of the surface negative N 1 component. Precise information about the system bandpass used should be included in published reports.

Unexpected latency shifts of the stationary P9 somatosensory evoked potential far field with changes in shoulder position

Early somatosensory evoked potential (SEP) components to median nerve stimulation were recorded with non-cephalic reference from scalp, neck and oesophagus in normal young adults. The nerve volley was recorded from the arm and Erbs point. The latencies of the stationary P9 far field were increased significantly by supporting the shoulder in a high position. This manoeuvre was shown in X-rays to change the axis of the nerve at levels between lateral and middle parts of the clavicle. This suggests that the far field is not related to inhomogeneities of the medium surrounding the nerve whereby abrupt changes in extracellular current flow might be produced as the volley arrives at a certain level. Rather, the axial orientation of the propagated dipole appears as a major factor determining the features of the stationary P9 far field. The reversible effect described does not significantly influence the conduction of the volley itself nor the latencies of the subsequent SEP components.

Automatic suppression of eye movement and muscle artifacts when averaging tape recorded cerebral evoked potentials

Abstract A method is described which allows the elimitation of eye blinks and other artifacts from the evoked potentials averaged from tape-stored EEG data. The method includes the reading at faster speed of the recorded tape in reverse (with respect to the initial record) into comparator and gate functions which write on a separate track a step function-during and before baseline shifts. The method consistently eliminates the inclusion of tape sections with spurious baseline shifts in the multichannel EEG samples subsequently averaged.

A random interval generator using beta ray emission

Abstract A solid generator of random intervals, based on a beta ray emitter, is described. The instrument provides for independent control of the minimal interval between successive output plus and of the dispersion of the random intervals. It has been used for delivering sensory stimuli at random intervals or in random sequences.

Stray Electric Field Due to the Carbon Foil Resistance in Hydrogen Beam-Foil-Spectroscopy Measurements

We have measured the linear polarization of the Hβ transition at 486.1 nm excited by passage of a 110 keV proton beam through perpendicular carbon foils. We have observed that the polarization depends upon the beam intensity and on the relative position of the foil and its holder. We have shown that these dependences are linked to the presence of a stray electric field at the immediate vicinity of the foil. The field is due to the potential distribution at the foil surface resulting from the electron radial flow in the high foil electric resistance (about 50 kΩ). It introduces a perturbation which in our case is more important than the temperature effect observed by Gay and Berry (Phys. Rev. A19, 952 (1979)). The field is proportional to the beam current density and is reduced for large foil and beam diameters.

A convenient stimulus and situation coding system for the tape recording of event related potentials

Abstract A low-cost versatile electronic coding apparatus is described for use in tape-recorded psychophysiological experiments. The first circuit serves to encode, to record in AM mode on tape and to retrieve the occurrence in time of four independent sensory stimuli, using only one tape track. The second is used to write in FM mode on another tape track any figure from 1 to 9 characterizing as many experimental situations. This apparatus is reliable and helpful for the automatic averaging of event-related cerebral potentials in complex psychological situations.

Electromechanical drive employing negative feedback for Mössbauer experiments

Abstract A servomechanism of an electrodynamic system used in Mossbauer spectrometry with linear or constant velocity is described.

Ion beam current dependence of secondary electron emission from thin carbon foils

Abstract The secondary electron yield and the mean charge of the beam have been measured as a function of the beam current. We have shown that the observed current dependence is not a temperature effect.

Recording of simultaneous multi-detector neutron decay curves

Abstract Separation of harmonics in pulsed neutron source experiments may be effected by measuring the neutron decay at several points of the medium. A pulse generator allowing for the simultaneous recording of four neutron decay curves with a time analyzer having a single detector input is described.

Real Time Image Enhancement By Simple Video Systems

In image processing, digital systems give the highest flexibility in the sense that they allow in general to solve many problems by only changing software.