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Evoked responses by median computation
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amplitude of component 1 remained unchanged. The same was confirmed also during sleep, though the EHG, without overt lever pressing, showed only phasic activities. Latency of the maximal amolitude of C4-5 from the CS onset oositivelv co&elated to that of the EMG onset both during fast and slow wave sleep and wakefulness. Prior to conditioning, however, no augmentation of C4-5 appeared immediately preceding spontaneous EtlG activities of the forelimb during the sleep These results suggest that the central stages. CR, as revealed by the augmentation of the evoked potentials, accompanied by the conditioned EflG activities, can be observed during fast and slow wave sleep.
due to the two filtering versions were compared for different trial (averaging numbers. The fact that the spec i ra of the signal and the noise are unknowns and, in addition, the signal power is much smaller than the noise oower is resoonsiblefor the difficultv in the ipplication 'of Wiener filtering to a&al evoked responses. If such unknown power spectra are inferred appropriately, Wiener filtering may provide satisfactory estimates within a relatively small number of trials.
C-12.05 COMPUTED MAPPING OF ELECTROENCEPHALOGRAF",(CrlE) Ir! TRANSIEF!T ISCHEMIC ATTACKS: A COMPARATIVE STUDY WITH THE CONVENTIONAL EEG. W. Hirano, M. Endo, K. Nagata, T. Kawase and 1"1.llizukami (Toyama, Japan)
The conventional ensemble averaging technique has come to be widely used for the analysis of evoked responses recorded from the central nervous system and yields an unbiased estimate of the evoked response embedded in the spontaneous background activity. This technique, however, has a fundamental fault that the estimate is sensitively affected by unexpected instrumental artifacts and a large sample size is required to obtain a satisfactory result. In the present study, we develop a new method to detect the evoked response and investigate the various properties within the visual and auditory evoked responses. This method is concerned with a median computation of observed data and gives an unbiased estimate of the true evoked response. We provide a comparative study of these two meth'ods and give it our general considerationbased on the results of analysis of numerical simulations and experimentation. When the variance of background activity is small, as a matter of course, the results obtained by these methods coincide with each other. It is shown that our method yields a robust and stable result against an extraordinary datum when the background activity fluctuates extremely.
The conventional EEG was very useful for detecting functional lesions intransientischemic attacks (TM) even after the complete recovery from the attacks. Now a newly developed microcomputed system of EEG which can display equipotential maps of square roots of average power spectra over each frequency band on color television has been used to detect functional lesions in TIA, comparing with the conventional EEG. 20 patients with TIA of transient motor weakness or aphasia were studied by the above methods on line. In the conventional EEG abnormal findings with sporadic theta waves were observed in 14 out of 20 patients (70%). On Cr?E, low voltage alpha foci were displayed in 10 patients and hiqh voltage slow foci in 6 patients, and their correspondence with the functional lesions was observed in 12 out of 20 patients (60%). As compared with the conventional EEG, abnormal findings in the alpha band were more detectable on CME, but sporadic slow waves were less so in TIA. D-$18.05 APPLICABILITY OF WIENER FILTERING TO AVERAGED EVOKED POTENTIALS. T. F!ogawa, K. Katayama, Y. Tabata, T. Oshio and T. Kawahara (Moriguchi, Japan) Wiener filtering proposed by D.O. Walter (1969) and its modification due to D.J. Doyle (1975) for averaged evoked potentials were applied to visual and brain-stem auditory evoked potentials in order to test the efficiency of the methods in the estimation of actual evoked responses. Reduction of noise due to averaging for different trial numbers were examined by calculating the power spectra of the noisy signals for various trial numbers. In terms of such data, unknown power spectra of the signal and the noise were inferred by virtue of s&era1 estimation formulae. The filtered wave forms
A posteriori
D-18.04 EVOKED RESPONSES BY MEDIAN COMPUTATION. T. Nogawa, K. Katayama, Y. Tabata, T. Ohshio and T. Kawahara (r?origuchi, Japan)
B-7.08 VISUAL EVOKED POTENTIALS IN CEREBROVASCULAR DISEASE. V. Thorwirth (Seesen, W. Germany) Investigation of visual evoked potentials (VEP) by means of checkerboard inversion gives values with good reproducibility and low standard deviation for the latencies and amplitudes of VEP. In patients with scanty symptoms of cerebrovascular disease and without visual field defects. .we found either differences if VEP amplitudes from one side to the other of over 25% (in relation to larger value) or very small absolute values of the amplitudes (smaller than 3 pV) as pathological values compared to control SUDjects. The latencies were normal. This method ._of investigation helps towards objective analysis of functional disturbances in patients with cerebrovascular diseases. Furthermore, comparative investigations in patients with cerebral I
amplitude of component 1 remained unchanged. The same was confirmed also during sleep, though the EHG, without overt lever pressing, showed only phasic activities. Latency of the maximal amolitude of C4-5 from the CS onset oositivelv co&elated to that of the EMG onset both during fast and slow wave sleep and wakefulness. Prior to conditioning, however, no augmentation of C4-5 appeared immediately preceding spontaneous EtlG activities of the forelimb during the sleep These results suggest that the central stages. CR, as revealed by the augmentation of the evoked potentials, accompanied by the conditioned EflG activities, can be observed during fast and slow wave sleep.
due to the two filtering versions were compared for different trial (averaging numbers. The fact that the spec i ra of the signal and the noise are unknowns and, in addition, the signal power is much smaller than the noise oower is resoonsiblefor the difficultv in the ipplication 'of Wiener filtering to a&al evoked responses. If such unknown power spectra are inferred appropriately, Wiener filtering may provide satisfactory estimates within a relatively small number of trials.
C-12.05 COMPUTED MAPPING OF ELECTROENCEPHALOGRAF",(CrlE) Ir! TRANSIEF!T ISCHEMIC ATTACKS: A COMPARATIVE STUDY WITH THE CONVENTIONAL EEG. W. Hirano, M. Endo, K. Nagata, T. Kawase and 1"1.llizukami (Toyama, Japan)
The conventional ensemble averaging technique has come to be widely used for the analysis of evoked responses recorded from the central nervous system and yields an unbiased estimate of the evoked response embedded in the spontaneous background activity. This technique, however, has a fundamental fault that the estimate is sensitively affected by unexpected instrumental artifacts and a large sample size is required to obtain a satisfactory result. In the present study, we develop a new method to detect the evoked response and investigate the various properties within the visual and auditory evoked responses. This method is concerned with a median computation of observed data and gives an unbiased estimate of the true evoked response. We provide a comparative study of these two meth'ods and give it our general considerationbased on the results of analysis of numerical simulations and experimentation. When the variance of background activity is small, as a matter of course, the results obtained by these methods coincide with each other. It is shown that our method yields a robust and stable result against an extraordinary datum when the background activity fluctuates extremely.
The conventional EEG was very useful for detecting functional lesions intransientischemic attacks (TM) even after the complete recovery from the attacks. Now a newly developed microcomputed system of EEG which can display equipotential maps of square roots of average power spectra over each frequency band on color television has been used to detect functional lesions in TIA, comparing with the conventional EEG. 20 patients with TIA of transient motor weakness or aphasia were studied by the above methods on line. In the conventional EEG abnormal findings with sporadic theta waves were observed in 14 out of 20 patients (70%). On Cr?E, low voltage alpha foci were displayed in 10 patients and hiqh voltage slow foci in 6 patients, and their correspondence with the functional lesions was observed in 12 out of 20 patients (60%). As compared with the conventional EEG, abnormal findings in the alpha band were more detectable on CME, but sporadic slow waves were less so in TIA. D-$18.05 APPLICABILITY OF WIENER FILTERING TO AVERAGED EVOKED POTENTIALS. T. F!ogawa, K. Katayama, Y. Tabata, T. Oshio and T. Kawahara (Moriguchi, Japan) Wiener filtering proposed by D.O. Walter (1969) and its modification due to D.J. Doyle (1975) for averaged evoked potentials were applied to visual and brain-stem auditory evoked potentials in order to test the efficiency of the methods in the estimation of actual evoked responses. Reduction of noise due to averaging for different trial numbers were examined by calculating the power spectra of the noisy signals for various trial numbers. In terms of such data, unknown power spectra of the signal and the noise were inferred by virtue of s&era1 estimation formulae. The filtered wave forms
A posteriori
D-18.04 EVOKED RESPONSES BY MEDIAN COMPUTATION. T. Nogawa, K. Katayama, Y. Tabata, T. Ohshio and T. Kawahara (r?origuchi, Japan)
B-7.08 VISUAL EVOKED POTENTIALS IN CEREBROVASCULAR DISEASE. V. Thorwirth (Seesen, W. Germany) Investigation of visual evoked potentials (VEP) by means of checkerboard inversion gives values with good reproducibility and low standard deviation for the latencies and amplitudes of VEP. In patients with scanty symptoms of cerebrovascular disease and without visual field defects. .we found either differences if VEP amplitudes from one side to the other of over 25% (in relation to larger value) or very small absolute values of the amplitudes (smaller than 3 pV) as pathological values compared to control SUDjects. The latencies were normal. This method ._of investigation helps towards objective analysis of functional disturbances in patients with cerebrovascular diseases. Furthermore, comparative investigations in patients with cerebral I