46 research outputs found
Disentangling neural processing of masked and masking stimulus by means of event-related contralateral – ipsilateral differences of EEG potentials
In spite of the excellent temporal resolution of event-related EEG potentials
(ERPs), the overlapping potentials evoked by masked and masking stimuli are hard
to disentangle. However, when both masked and masking stimuli consist of pairs
of relevant and irrelevant stimuli, one left and one right from fixation, with
the side of the relevant element varying between pairs, effects of masked and
masking stimuli can be distinguished by means of the contralateral preponderance
of the potentials evoked by the relevant elements, because the relevant elements
may independently change sides in masked and masking stimuli. Based on a
reanalysis of data from which only selected contralateral-ipsilateral effects
had been previously published, the present contribution will provide a more
complete picture of the ERP effects in a masked-priming task. Indeed, effects
evoked by masked primes and masking targets heavily overlapped in conventional
ERPs and could be disentangled to a certain degree by contralateral-ipsilateral
differences. Their major component, the N2pc, is interpreted as indicating
preferential processing of stimuli matching the target template, which process
can neither be identified with conscious perception nor with shifts of spatial
attention. The measurements showed that the triggering of response preparation
by the masked stimuli did not depend on their discriminability, and their
priming effects on the processing of the following target stimuli were
qualitatively different for stimulus identification and for response
preparation. These results provide another piece of evidence for the
independence of motor-related and perception-related effects of masked
stimuli
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In vivo functional neurochemistry of human cortical cholinergic function during visuospatial attention
Cortical acetylcholine is involved in key cognitive processes such as visuospatial attention. Dysfunction in the cholinergic system has been described in a number of neuropsychiatric disorders. Levels of brain acetylcholine can be pharmacologically manipulated, but it is not possible to directly measure it in vivo in humans. However, key parts of its biochemical cascade in neural tissue, such as choline, can be measured using magnetic resonance spectroscopy (MRS). There is evidence that levels of choline may be an indirect but proportional measure of acetylcholine availability in brain tissue. In this study, we measured relative choline levels in the parietal cortex using functional (event-related) MRS (fMRS) during performance of a visuospatial attention task, with a modelling approach verified using simulated data. We describe a task-driven interaction effect on choline concentration, specifically driven by contralateral attention shifts. Our results suggest that choline MRS has the potential to serve as a proxy of brain acetylcholine function in humans
Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine
[This corrects the article DOI: 10.1186/s13054-016-1208-6.]
Komplikationen nach laparoskopischer Cholecystektomie - hilft die postoperative Routinesonographie weiter?
Spatial S-R compatibility with centrally presented stimuli: An event-related asymmetry study on dimensional overlap
Experimental determination of tantalum L shell fluorescence yields and Coster Kronig transition probabilities
Using radiometrically calibrated instrumentation of the Physikalisch Technische Bundesanstalt, the L shell fluorescence yields and Coster Kronig factors of tantalum including the uncertainty budget were experimentally determined based on transmission and X ray fluorescence experiments. The determined fluorescence yields amp; 969;L3 0.247 12 , amp; 969;L2 0.278 15 , amp; 969;L1 0.157 12 were independently validated through XRR GIXRF experiments. Both the Coster Kronig factors f23 0.123 84 , f13 0.328 152 , f12 0.14 11 as well as the fluorescence yields are in good agreement with the most established databases in the field of X ray fluorescenc