5,574 research outputs found
Die Welt jenseits der Oszillografen : ein Streitgespräch zwischen dem Hirnforscher Wolf Singer und dem Philosophen Marcus Willaschek
No full textNeurowissenschaftler fordern einen illusionslosen Umgang mit Begriffen wie Willensfreiheit und Bewusstsein. Philosophen kritisieren offen die Thesen von Hirnforschern. Stehen sich diese Positionen unversöhnlich gegenüber? Wo gibt es Möglichkeiten einer Annäherung, gar einer Kooperation? Der Religionsphilosoph Prof. Dr. Thomas M. Schmidt und der Biologe Stefan Kieß loten die Situation in Frankfurt aus; ihre Gesprächspartner sind der Hirnforscher Prof. Dr. Wolf Singer (links), Direktor am Max-Planck-Institut für Hirnforschung, und Prof. Dr. Marcus Willaschek (rechts), Philosoph an der Universität Frankfurt
Distributed processing and temporal codes in neuronal networks
No full textThe cerebral cortex presents itself as a distributed dynamical system with the characteristics of a small world network. The neuronal correlates of cognitive and executive processes often appear to consist of the coordinated activity of large assemblies of widely distributed neurons. These features require mechanisms for the selective routing of signals across densely interconnected networks, the flexible and context dependent binding of neuronal groups into functionally coherent assemblies and the task and attention dependent integration of subsystems. In order to implement these mechanisms, it is proposed that neuronal responses should convey two orthogonal messages in parallel. They should indicate (1) the presence of the feature to which they are tuned and (2) with which other neurons (specific target cells or members of a coherent assembly) they are communicating. The first message is encoded in the discharge frequency of the neurons (rate code) and it is proposed that the second message is contained in the precise timing relationships between individual spikes of distributed neurons (temporal code). It is further proposed that these precise timing relations are established either by the timing of external events (stimulus locking) or by internal timing mechanisms. The latter are assumed to consist of an oscillatory modulation of neuronal responses in different frequency bands that cover a broad frequency range from 40 Hz (gamma) and ripples. These oscillations limit the communication of cells to short temporal windows whereby the duration of these windows decreases with oscillation frequency. Thus, by varying the phase relationship between oscillating groups, networks of functionally cooperating neurons can be flexibly configurated within hard wired networks. Moreover, by synchronizing the spikes emitted by neuronal populations, the saliency of their responses can be enhanced due to the coincidence sensitivity of receiving neurons in very much the same way as can be achieved by increasing the discharge rate. Experimental evidence will be reviewed in support of the coexistence of rate and temporal codes. Evidence will also be provided that disturbances of temporal coding mechanisms are likely to be one of the pathophysiological mechanisms in schizophrenia
Ist der Geist also doch an Materie gebunden? : Anmerkungen zu einem Essayband des Hirnforschers Wolf Singer
No full textRezension zu: Der Beobachter im Gehirn : Essays zur Hirnforschung / Wolf Singer. - Frankfurt : Suhrkamp Verl., 2002. - 238 S. ISBN 3-518-29171-8, 11 Euro
Subjective and objective learning effects dissociate in space and in time
No full textPerceptual learning not only improves sensitivity, but it also changes our subjective experience. However, the question of how these two learning effects relate is largely unexplored. Here we investigate how subjects learn to see initially indiscriminable metacontrast-masked shapes. We find that sensitivity and subjective awareness increase with training. However, sensitivity and subjective awareness dissociate in space: Learning effects on performance are lost when the task is performed at an untrained location in another quadrant, whereas learning effects on subjective awareness are maintained. This finding indicates that improvements in shape sensitivity involve visual areas up to V4, whereas changes in subjective awareness involve other brain regions. Furthermore, subjective awareness dissociates from sensitivity in time: In an early phase of perceptual learning, subjects perform above chance on trials that they rate as subjectively invisible. Later, this phenomenon disappears. Subjective awareness is thus neither necessary nor sufficient for achieving above-chance objective performance.</jats:p
Sensitivity and perceptual awareness increase with practice in metacontrast masking
No full textCan practice effects on unconscious stimuli lead to awareness? Can we "learn to see"? Recent evidence suggests that blindsight patients trained for an extensive period of time can learn to discriminate and consciously perceive stimuli that they were previously unaware of. So far, it is unknown whether these effects generalize to normal observers. Here we investigated practice effects in metacontrast masking. Subjects were trained for five consecutive days on the stimulus onset asynchrony (SOA) that resulted in chance performance. Our results show a linear increase in sensitivity (d') but no change in bias (c) for the trained SOA. This practice effect on sensitivity spreads to all tested SOAs. Additionally, we show that subjects rate their perceptual awareness of the target stimuli differently before and after training, exhibiting not only an increase in sensitivity, but also in the subjective awareness of the percept. Thus, subjects can indeed "learn to see.
On Stage at Wolf Trap: Karen Akers. Episode 205
No full textActress and singer Karen Akers brings her cabaret act to the Barns at Wolf Trap in Virginia, performing songs by Stephen Sondheim, Andrew Lloyd Webber, Craig Carnelia, Jacques Brel, Peter Allen, and Leonard Bernstein. Music director and pianist Mark Hummel duets on several numbers. Akers is also supported by Jay Lenhart (electric bass and guitar), Andy Drelles (horns and reeds), and James Saporito (percussion)
On Stage at Wolf Trap: Wyndom Hill Evening. Episode 202
No full textAn evening of new-age music features Will Ackerman, guitarist and founder of Windham Hill Records; acoustic guitarist and singer-songwriter Michael Hedges; and the electronic musical group Shadowfax. Music includes "Hawk Circle," "All Along the Watchtower," "Because It's There," "Shadowdance," "Brown Rice" and "Streetnoise." Performance from the Wolf Trap National Park for the Performing Arts in Virginia
Stimulus predictability reduces responses in primary visual cortex
No full textIn this functional magnetic resonance imaging study we tested whether the predictability of stimuli affects responses in primary visual cortex (V1). The results of this study indicate that visual stimuli evoke smaller responses in V1 when their onset or motion direction can be predicted from the dynamics of surrounding illusory motion. We conclude from this finding that the human brain anticipates forthcoming sensory input that allows predictable visual stimuli to be processed with less neural activation at early stages of cortical processing
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