Christof Koch

..Its conclusions support the hypothesis that visual consciousness does not arise from neurons in primary visual cortex and forces a reinterpretation of numerous prior studies...

..Taken together, these results suggest that the contents of visual awareness reflect neuronal activity in certain extrastriate, but not in striate, visual cortical areas...

..Such dissociations are easier to understand when the different functions of these two processes are considered. Untangling their tight relationship is necessary for the scientific elucidation of consciousness and its material substrate...

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..This is reflected in their function, their evolutionary history, their structure, and the coding schemes they use to represent information. These four viewpoints need all play a role in any future science of "brain complexity."..

..On the basis of the firing of these MTL neurons, the dynamics of the competition between visual images in the subject's mind was visualized on an external display...

..This selectivity appeared to be independent of emotional valence or arousal and may reflect the importance that animals held throughout our evolutionary past...

..Combining spiking and LFP activity enhanced the decoding accuracy in comparison with the accuracy obtained with each signal alone, especially for short time intervals...

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..These results point to a coherent picture of how spatial attention and top-down task-based attention interact in visual cortex...

..This suggests that the primate visual system allocates attention using such an enhanced saliency map...

..Consequently, and contrary to several previously published findings, our results demonstrate that attentional limitations, rather than target recognition alone, affect the detection of targets in rapidly presented visual sequences...

..This dissociation of objective performance and subjective confidence suggests that attention and awareness, as measured by confidence, are distinct, albeit related, phenomena...

..These results are compatible with a rapid subcortical pathway generating accurate saccades to salient targets after analysis by cortical mechanisms...

..Small variations of a few key parameters account well for the intersubject differences. The model is compatible with neurophysiological findings of V4 and frontal eye fields (FEF) neurons and predicts the gain modulation of these cells...

..Our findings indicate that endogenous brain activity can causally affect neural function through field effects under physiological conditions...

..The learning rule is also applicable to a neuron with multiple-direction-selective subunits and to a pair of cells with opposite-direction selectivities and is stable under different starting conditions, delays, and velocities...

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..Additionally, substantial power can be generated in the 90-150 Hz epsilon band by the APs of rhythmically firing pyramidal neurons. Thus, high-frequency LFPs may generally contain signatures of local cell assembly activation...

..As models of these interactions become more accurate in predicting behaviorally-relevant salient locations, they become useful to a range of applications in computer vision and human-machine interface design...

..Additionally, we find that the generation and forward propagation of dendritic Ca(2+) spikes are susceptible to channel variability. This indicates limitations on computations that depend on the precise timing of Ca(2+) spikes...

..Regarding sight recovery after early blindness, our results further demonstrate that cross-modal responses coexist with regained visual responses within the visual cortex...

..Thus, cross-modal or cognitive interference that does not affect the visibility of the face does not interfere with the face aftereffect. We conclude that adaptation to face identity depends on seeing the face...

..In conclusion, using a detailed spiking network model we find biophysical mechanisms and limitations of saliency computations which can be tested experimentally...

..In contrast, this prediction was at chance for incorrect, unattended trials. The firing rates of visually selective MTL cells thus constitute a neural correlate of change detection...

..These findings imply that local electric fields, generated by the cooperative action of brain cells, can influence the timing of neural activity...

..Our findings provide evidence that deviations from surrounding statistics, rather than contrast per se, underlie the well-established relation of contrast to fixation...

..Based on these results, we conclude that EAP recordings are an excellent source of data for the purpose of constraining compartmental models...

..We conclude that there is a significant gap in our present understanding of either the spike-generation process in pyramidal neurons, the biophysics of extracellular recording, or both...

..We found a consistent AB for both target categories but the duration of the AB depended on the target category...

..Potential applications include designing reward schemes to improve detection of life-critical, rare targets (e.g., cancers in medical images)...

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..Our findings suggest that the rating of image conspicuity is driven by image-immanent, sensory factors common to all observers...

..This method will serve as a starting point in connecting the microscopic generation of electric fields at the level of neurons to macroscopic observables such as the local field potential...

..These findings provide clear evidence for distinctive influences of selective attention and consciousness on visual perception...

..Our results support the view that CFS is not a stronger version of BR but is due to the accumulated suppressive effects of multiple flashes...

..Control experiments are compatible with the hypothesis that the nonsensory hemodynamic signal is mediated by top-down spatial attention, linked to (but separate from) awareness of the change...

..Our quantitative model reproduces important voltage- and frequency-dependent features of the data, accounting for the 1/f behavior, as well as the effects of various blockers...

..This suggests that individuals are able to harvest rewards optimally and dynamically under time pressure while seeking multiple targets embedded in perceptual clutter...

..Two-bar interaction maps showed reversed excitation and inhibition regions when two different contrast bars are presented...

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..These results shed light on neural mechanisms of attentional competition, and representational capacity at different levels of the human visual system...

..These results suggest that the visual system is well able to make complex judgments of natural stimuli, even when attention is not fully available...

..Interestingly, each cell's dendritic morphology had very little impact on the EAP waveform. The model also demonstrates that the varied composition of ionic currents in different cells is reflected in the features of the EAP...

..The magnitude of this induced voltage can be several mV, does not spread electrotonically, and depends only weakly on the passive properties of the cable. We discuss their possible functional relevance...

..e. the first presented vernier dominates performance. Therefore, feature fusion can neither be explained completely by spatially local mechanisms nor by the temporal order of appearance of elements...

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..Rather, we found that such loops allow the masked stimulus to reverberate in the visual system and affect behavior for nearly 150 msec after the feed-forward sweep...

..These results are consistent with an implementation of multiplication based on dendritic subtraction of two converging inputs encoded logarithmically, followed by exponentiation through active membrane conductances...

..We conclude that some visual tasks associated with "high-level" cortical areas may proceed in the near absence of attention...

..Our results imply that formation of afterimages involves neuronal structures that access input from both eyes but that do not correspond directly to the neuronal correlates of perceptual awareness...

..Here, we used a probabilistic analysis to show that these data are consistent with a sparse code in which neurons respond in a selective manner to a small fraction of stimuli...

..These results demonstrate that brain regions known to be involved in other aspects of learning and memory also play a specific role, reflecting on each trial the acquisition and representation of contingency awareness...

..In other words, visual search and dual-task performance reveal attentional resources along two independent dimensions. We suggest an interpretation of these results in terms of neuronal selectivities and receptive field size effects...

..A motion-energy model, coupled with attention-dependent temporal subsampling of the perceptual stream at rates between 10 and 20 Hz, can quantitatively account for the observed data...

..These data are compatible with the idea that motion perception occurs in snapshots <100 ms in duration...

..We conclude that the sensory neurons are specialized to acquire information accurately with little processing, whereas the following stage extracts behaviourally relevant features, thus performing a nonlinear pattern-recognition task...

..Moreover, contrary to expectations based on earlier studies, we find that the noisy spike encoding models encode slowly varying stimuli more effectively than rapidly varying ones...

..Given the very sparse and abstract representation of visual information by these neurons, they could in principle be considered as 'grandmother cells'. However, we give several arguments that make such an extreme interpretation unlikely...

..The feasibility of decoding sensory information from human extracellular recordings has implications for the development of brain-machine interfaces...

..For all subthreshold voltage ranges, the quasi-active linearized approximation is accurate within 8% and may thus be used in large-scale simulations of realistic neuronal geometries...

..These results suggest an invariant, sparse and explicit code, which might be important in the transformation of complex visual percepts into long-term and more abstract memories...

..By combining the output of feature maps via a series of nonlinear classifiers, the new model consistently predicts eye movements better than any of its competitors...

..This independence of spatial overlap provides an advantage to the visual system, allowing conflict resolution when an object is nonstationary on the retina (e.g., during frequently occurring eye movements)...

..Therefore, the activity of most individual neurons in the medial temporal lobe of naive human subjects directly correlates with the phenomenal visual experience...

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..These data suggest that trace conditioning may be useful for studying neural substrates of attention in mice, and implicate the ACC as one such substrate...

..Separating the effects of selective visual attention from those of visual consciousness is of paramount importance to untangle the neural substrates of consciousness from those for attention...

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..Our results provide further evidence against the notion that only low-level representations can be accessed outside the focus of attention...

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..A postexperimental questionnaire showed a positive correlation between conditioning and awareness for differential trace conditioning extinction...

..This results in enhanced performance in a compact, low-power CMOS motion sensor. Our silicon system also demonstrates that modern, biophysically-detailed models of neural sensory processing systems can be instantiated in VLSI hardware...

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..Our results show that MIB does not affect the persistence and intensity of afterimages. Thus, there is no significant contribution to the formation of afterimages beyond the sites mediating MIB...

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..We demonstrate that the suggested model can enable a model of object recognition in cortex to expand from recognizing individual objects in isolation to sequentially recognizing all objects in a more complex scene...

..These data strongly support the consolidation theory of hippocampus function and implicate the mPFC as a site of long-term memory storage/retrieval...

..Furthermore, we demonstrate a proof-of-concept implementation for sharing complex features between recognition and attention as a mode of top-down attention to particular objects or object categories...

..There, stimulus-induced coincident activity can improve the extraction of behaviorally relevant features from the stimulus...

..But once subjects recognize more semantic-level components of a scene, there is little evidence suggesting any bias toward either scene-level or object-level recognition...

..We also outline some general experimental approaches to the problem and, finally, acknowledge some relevant aspects of the brain that have been left out of the proposed framework...

..This article explores the contributions of neurosurgeons to this quest and outlines some of the results that have already been achieved...

..Finally, we briefly consider how a theoretical analysis of the fundamental properties of consciousness can usefully complement neurobiological studies...

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..Invariance appears to be in part due to non-linear integration of synaptic inputs within the dendritic tree of this neuron...

..Our research plan will lead to a quantitative picture of the properties of neuronal noise sources and their effect on the information capacity of individual cortical neurons. ..

..Support is requested in each year for ten predoctoral CNS trainees. ..