A posteriori time-varying filtering of averaged evoked potentials. II. Mathematical and computational aspects.

The problem of estimating an unknown transient signal, given an ensemble of waveforms, in which this signal appears as a nonrandom component in the presence of additive noise is considered. This problem is solved by generalizing the method of "a posteriori 'Wiener' filtering". In the new method, the ensemble average is filtered by a time-varying system which is based on estimated time-varying power spectra of signal and noise.

Spectro-temporal representations and time-varying spectra of evoked potentials. A methodological investigation.

Evoked potential waveforms are generally of a dynamic, transient character. Consequently, their spectral energy distribution cannot be adequately described by time-invariant representations, such as the power density spectrum. Obviously, a spectro-temporal description is needed.

The discriminating role of EEG power spectra in dyslexic children.

The aim of this investigation is to compare EEG power-density spectra between dyslexic and normal children. The children have been selected on the basis of specific reading and writing tasks; those with severe organic diseases and mental disorders were excluded. Groups aged 8, 9 and 10 years have been compared.

[The effects of ordinary provocation on the power density spectrum. A clinical electroencephalographic study (author's transl)].

In the search for methods which might increase the discrimination of the EEG, the power density spectra of a random sample of patients during different conditions were analysed. Power density spectra were made during eyes closed, eyes open, after hyperventilation, during photic stimulation, and during auditory stimulation. It proved that the spectra may change under different provocation tests, sometimes in a rather peculiar way.

Cortical and cervical somatosensory evoked responses in demyelinating diseases.

In six patients suffering from a multifocal neurological disease of the demyelinating type, a somatosensory evoked response was analyzed in the cortical and cervical are after stimulating the right index finger and the right nervus suralis. The results of the investigation with this method indicate that localization of the central nervous system pathology seems to lie within the realms of possibility, in which case this method will be a useful addition to the tools used to evaluate quantitatively the results of different treatments in this type of disease.