We discuss the role of synchrony of activationin higher-level cognitive processes. Inparticular, we analyze the question of whethersynchrony of activation provides a mechanismfor compositional representation in neuralsystems. We will argue that synchrony ofactivation does not provide a mechanism forcompositional representation in neural systems.At face value, one can identify a level ofcompositional representation in the models thatintroduce synchrony of activation for thispurpose. But behavior in these models isalways produced by means conjunctiverepresentations in the form of coincidencedetectors. Therefore, models that rely onsynchrony (...) of activation lack the systematicityand productivity of true compositional systems.As a result, they cannot distinguish betweentype and token representations, which resultsin misrepresentations of spatial relations andpropositions. Furthermore, higher-levelcognitive processes will likely integrateinformation from widely distributed areas inthe brain, which puts severe restrictions onthe underlying neural dynamics if synchrony ofactivation is to play a role in theseprocesses. We will briefly discuss theserestrictions in the case of feature binding invisual cognition. (shrink)
Cognitive agents are dynamical systems but not quantitative dynamical systems. Quantitative systems are forms of analogue computation, which is physically too unreliable as a basis for cognition. Instead, cognitive agents are dynamical systems that implement discrete forms of computation. Only such a synthesis of discrete computation and dynamical systems can provide the mathematical basis for modeling cognitive behavior.
Various issues concerning the neural blackboard architectures for combinatorial structures are discussed and clarified. They range from issues related to neural dynamics, the structure of the architectures for language and vision, and alternative architectures, to linguistic issues concerning the language architecture. Particular attention is given to the nature of true combinatorial structures and the way in which information can be retrieved from them in a productive and systematic manner.
We discuss a visual blackboard architecture that could be involved in imagery. In this architecture, networks that process identity information interact with networks that process location information, in a manner that produces structural (compositional) forms of representation. Architectures of this kind can be identified in the visual cortex, but perhaps also in prefrontal cortex areas related with working memory.