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T Elbert

Publications and source records attributed to T Elbert.

27 records · Page 2Linked to original sources
PubMed1986

Slow brain potentials and the "tunnel effect".

The present study investigated electrocortical concomitants of the "tunnel effect." The tunnel effect refers to the following perceptual phenomenon: if a continuously moving object disappears behind a shield ("enters a tunnel") the observer has the impression that the same object continues to move with the time point of reappearance usually being underestimated. In the present study, an object moved across a tv-screen for 6 s; it either disappeared behind a shield (tunnel condition), disappeared at once (explosion condition), or remained visible until the end of its trajectory (control condition). Subjects had to press a button whenever they believed that the object had arrived at its trajectory's end. The object's flight was accompanied by a continuously rising slow negative shift of the EEG that resembled the contingent negative variation (CNV). Either type of object disappearance produced a positive-going potential that may reflect brain processes associated with memory rehearsal and/or time estimation. A late P300-like positivity was prominent under tunnel conditions only. Response latency was shorter under disappearance than under control conditions. The positive deflection is discussed as sign of amodal brain processing (memory rehearsal and/or time estimation). The P300-like wave elicited by the object's disappearance activates these memory representations. Based on these considerations, an attempt was made to interpret the premature motor responses, which are commonly observed for tunnel conditions but not for other time estimation tasks.

Brain↗
PubMed1986

Patterns of stimulus- and self-induced slow brain potentials--a sign of task-specific preparation.

Does the scalp distribution of slow shifts in human brain potentials depend upon the processing demands? The question was approached applying two different paradigms. In the first study, the anticipation of haptic tasks presented to either of the hands was found to give rise to a contralateral slow negative brain potential (SP). The second study demonstrated that comparable hemisphere-specific patterns can be self-induced by means of biofeedback training. These results suggest that negative SPs (like the CNV) indicate preactivation of those brain-regions that process the expected task.

Biofeedback, Psychology↗
PubMed1985

Removal of ocular artifacts from the EEG--a biophysical approach to the EOG.

The present paper describes the propagation of ocular potentials across the scalp on a biophysical basis. It is concluded that 3 EOG derivations (two for EEG records along the midline) are generally necessary to account for ocular disturbances in the EEG. The inadequacy of many methods suggested for EOG artifact control may be due to the false assumption that just one EOG derivation provides enough information to remove ocular potentials from any EEG recording along the mid(-sagittal) line. A comparison of compensation with one or with two EOG derivations is described for a data set of slow brain potentials. A frequency dependence of the ocular influence cannot be neglected, if fast and slow EOG activities have to be removed. The present considerations should allow a more theoretically based decision of the EOG correction method necessary for a certain data set.

Biophysical Phenomena↗
PubMed1985

Asymmetry of brain potentials related to sensorimotor tasks.

The present study investigates the hemispheric specificity of event-related (ERP) and slow potentials (SP) of the brain during preparation and performance of sensorimotor (haptic) tasks. Tasks were selected which have been assumed to be processed primarily by only one brain hemisphere. ERPs, SPs and spontaneous EEGs were obtained from both hemispheres (C3-C4, P3-P4) and from Fz and Cz in a constant foreperiod (6 s) paradigm. Warning and task stimuli comprised up to four tactile stimuli, applied to index and middle finger of each hand. To maximize lateralized processing, the right-hand task required counting, the left hand task pattern matching. Components of the ERP (N1, P3, SW) and of SPs show task-dependent lateral asymmetry with the larger amplitudes contralateral to the preparing and responding hand. Results confirm hemisphere-specific processing of the tactile tasks but quantification as indicated by ERP amplitudes show considerable activity in both hemispheres. The SP-distribution rather reflects task-specific preparation than general alertness or orienting.

Adult↗
PubMed1985

The perception of Necker cube reversal interacts with the Bereitschaftspotential.

Subjects observed a reversible figure (Necker cube), and were asked to switch a lever about twice a minute. The direction of the lever switch indicated whether a reversal of the Necker cube was just experienced or not experienced. The Bereitschaftspotential (BP, readiness potential) turned out to be smaller in amplitude but earlier in onset prior to the reversal, especially over fronto-central regions. During another condition a tonic background stimulation (achieved by a radio-play) was introduced. Distraction reduced the BP, mainly when no reversal was reported. The results suggest a dependency of pre-movement potentials from non-motoric, psychological variables.

Adult↗
PubMedDate not supplied

Area-specific self-regulation of slow cortical potentials on the sagittal midline and its effects on behavior.

Exteroceptive feedback was given for negative and positive shifts in slow potentials (SPs) recorded from Fz, Cz, or Pz (between groups design). Slow potentials at the feedback site were referred to adjacent scalp and non-cephalic electrodes, so as to confine SP shifts to the feedback location. Area-specific regulation of SPs was obtained at each midsagittal site after 3 days of feedback training. Subjects reported sensorimotor and emotional arousal when negative SP shifts were trained frontally, but not when negative shifts were trained parietally (cognitive/attentional strategies reported after parietal feedback). Area-specific regulation of SPs was subsequently abolished when behavioral tasks were added to further probe frontal/parietal differences (dual-task procedure). These findings indicate that area-specific self-regulation of SPs is possible on the sagittal midline, and that self-regulated parietal SPs (in contrast to frontal ones) arise from non-motoric generators. The source of SP self-regulation was more readily probed by verbal reports of feedback strategy than by study of dual-task relations, because feedback control was disrupted by the dual-task requirement.

Adult↗
PubMedDate not supplied

Vasopressin does not enhance memory processes: a study in human twins.

Behavioral effects of lysin-vasopressin (LVP) were investigated applying two paradigms from human experimental psychology. The first task was designed to simulate amnesic symptoms in normals. The second task addressed the emotional value of the items to be processed. Additionally, EEG recordings were used as indicators of the central nervous system effectiveness of LVP. Blood pressure and heart rate measured peripheral arousal. The co-twin control method was employed to increase experimental power. Contrary to the prediction of the vasopressin memory hypothesis none of the specific memory parameters was improved by LVP treatment. Changes in the electrical activity of the brain, but not in blood pressure and heart rate indicated central nervous system actions of LVP. However, interpretation of LVP effects in terms of memory processing seems not to be justified.

Adolescent↗