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A method is proposed to determine components of evoked scalp potentials, in terms of times of occurrence (latency) and location on the scalp (topography). The scalp field distributions were evoked by checkerboard reversal and were recorded simultaneously in 47 channels. Component latencies are defined as times of maximal values of the electrical power of(More)
  • W Skrandies
  • 1998
According to the 'semantic differential technique' the affective meaning of words can be quantified in statistically defined, independent dimensions where every word is uniquely located on the three dimensions evaluation ('good-bad'), potency ('strong-weak'), and activity ('active-passive'). Two experiments were performed on a total of 52 adults: first, 162(More)
Steps in brain information processing are reflected on the scalp as changes of the electric potential which is evoked by the stimulus. However, for a given recording point on the scalp, there is no absolute amplitude or phase information of the electric brain potential. This means that the shape of an evoked potential waveform which is recorded from a given(More)
Multichannel recordings are commonly presented as topographic maps series displaying the change of the potential distribution over time. When reviewing a sequence of potential maps it becomes obvious that there are epochs with only little activity (few field lines; small extrema values) while at other times the fields display high peaks and deep troughs(More)
A group of 24 patients with Parkinson's disease (PD) with normal fundi and normal visual acuities was examined electrophysiologically. Checkerboard reversal VEPs and ERGs (P-ERGs) at various contrast levels as well as photopic and scotopic luminance ERGs were recorded and compared with an age-matched group of controls. Earlier reported latency increases of(More)
The use of coherence is a well-established standard approach for the analysis of biomedical signals. Being entirely based on frequency analysis, i.e., on spectral properties of the signal, it is not possible to obtain any information about the temporal structure of coherence which is useful in the study of brain dynamics, for example. Extending the concept(More)
Rapid learning processes are crucial for human object recognition. We report here on the alterations in neurophysiological activity in the human brain induced by repeated presentation of visual stimuli. In psychophysical experiments the percentage of correct responses increased significantly within less than 30 minutes in untrained observers. This(More)
  • W Skrandies
  • 1985
The temporal sensitivity of the visual system was investigated in fifteen healthy subjects by determining the critical flicker fusion frequency (CFF) and the performance in a double flash discrimination (DFD) task. Measurements were obtained using a small test light of 2.5 degrees diameter in the fovea and at eight different perifoveal retinal locations(More)
Scalp potential fields in human subjects were evoked by checkerboard reversals to the upper and lower hermiretinae, using 1.6 and 3.2 reversals/s. Averaged fields were sampled along a saggital midline row of electrodes (field profiles) in 20 subjects, and from a 47 electrode array (field maps) in five subjects. In five subjects, profile peaks and troughs(More)
Electroencephalographic data recorded for topographical analysis constitute multidimensional observations, and the present paper illustrates methods of data analysis of multichannel recordings where components of evoked brain activity are identified quantitatively. The computation of potential field strength (Global Field Power, GFP) is used for component(More)