Trends in Cognitive Sciences
OpinionTemporal binding and the neural correlates of sensory awareness
Section snippets
Binding and consciousness
The notion of binding has been introduced first in the context of feature integration 9 and perceptual segmentation 10. Subsequently, the concept of binding has been applied to other domains and is now employed in theories on object recognition 11, attention 12, memory formation and recall 13, motor control 14, sensorimotor integration 15, language processing 16 and logical inference 17. In all these domains, a set of related computational requirements has been identified which, taken together,
Temporal binding
The concept of dynamic binding by synchronization of neuronal discharges has been developed mainly in the context of perceptual processing. Clearly, sensory systems (at least those of mammals) provide paradigmatic examples for functional architectures that give rise to binding problems of the kind defined above. The most dramatic case is represented by the primate visual system where anatomical and physiological studies have led to the identification of more than 30 distinct visual cortical
Animal studies on synchrony and awareness
By now, the synchronization phenomena predicted by the temporal binding hypothesis have been documented for a wide variety of neural systems. It is well established that neurons in both cortical and subcortical centers can synchronize their discharges with a precision in the millisecond range. The results available from animal studies show that synchronization of neural discharges occurs with a surprising degree of ubiquity, both across systems and species. Box 1 presents an overview of studies
Human studies on timing and perceptual consciousness
In humans, numerous studies using the technique of electroencephalographic (EEG) or magnetoencephalographic (MEG) recording have provided evidence supporting the conclusions drawn above. An important methodological difference is that the signals recorded in EEG/MEG studies result from spatial averaging across large neuronal assemblies and, thus, at this macroscopic level the cellular processes of synchronization and oscillatory response structure cannot be dissociated. Rather, both phenomena
Conclusions: synchrony and conscious states
The studies reviewed above strongly suggest that the temporal dynamics in neuronal activity may be critical for the production of conscious states. The experiments on binocular rivalry make it very likely that only strongly synchronized neuronal signals contribute to awareness. They suggest that activation of feature-detecting cells is per se not sufficient to grant access of the encoded information to consciousness (as indicated by the fact that cells representing a non-perceived stimulus are
Outstanding questions
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Why does selection based on temporal binding lead to awareness in some cases but not in others? For instance, both the attentive search for a particular object as well as the visuomotor coordination in a frequently practised task such as driving require context-dependent selection. However, although in the former case the selection process usually leads to awareness, this does not necessarily hold for the latter. What makes the difference?
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Assuming that the processes discussed here constitute
Acknowledgements
We thank Thomas Metzinger, Peter König and Olivier Bertrand for critical reading and comments on the manuscript. We are obliged to Matthias Munk, Pascal Fries and Michael Brecht for permission to use their data in Fig. 1–3. The authors’ research was supported by the Max-Planck-Society and the German Research Council (DFG grants EN 203/4-2 and EN 203/5-1/5-2).
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