The usefulness of contextually guided processors is investigated a little further. A more general use for binding V1 cell responses than the one in Phillips & Singer's target article is proposed, which takes into account that strong responses of these cells can mean more than the presence of lines and edges. The possibility of different grouping depending on the activities of neighboring cells is essential to the approach.

Since learning emerges from a circuit mediating behavior it is unrealistic to require LTP to be a sufficient explanation of it; however, LTP is a necessary component of some learning circuits. The properties of that component bear a closer formal relationship to the acquisition of associative strength than to the modulation of attention.

Well-posed questions about information processing may require physiologically based, quantitative models of large scale neocortical dynamic function. “Synchronization” of this dynamics can be viewed in different contexts of the binding problem.

Although the idea that cognitive structure changes as we learn is welcome, a variety of mathematical structures are needed to model the neural and cognitive processes involved. A specific example of bodily-kinaesthetic intelligence is given, building on a formalism given elsewhere. As the structure of cognition changes, previous learning can become tacit, adding to the complexity of cognition and its modeling.

We suggest that neither selectionism nor constructivism alone are responsible for learning-based changes in the brain. On the basis of quantitative structural studies of human brain tissue it has been possible to find evidence of both increase and decrease in tissue mass at synaptic and dendritic levels. It would appear that both processes are involved in the course of learning-dependent changes.

Deictic coding offers a useful model for understanding the interactions between the dorsal and ventral streams of visual processing in the cerebral cortex. By extending Ballard et al.'s ideas on teleassistance, I show how dedicated low-level visuomotor processes in the dorsal stream might be engaged for the services of high-level cognitive operations in the ventral stream.

Ballard et al. claim that fixations bind variables to cognitive pointers. I comment on three aspects of this claim: (1) its contribution to the interpretation of indexical language; (2) empirical support for the use of very few deictic pointers; (3) nonetheless, abstract pointers cannot be taken as prototypical cognitive representations.

This commentary describes some extensions of the Phillips & Singer model of contextual interactions to cater for the contrast- and extent-dependency of surround facilitation and suppression. I also comment briefly on some semantic problems with what exactly the role of synchronization might be: input preprocessing or output postprocessing?

Simulations and analytic considerations show that synchronisation occurs in delay neural networks at the surrounds of externally driven sites. In the synchronous fields, network transmission has a static transfer function and H(X|R,C) is minimal. But when autonomous local states with attractor dynamics develop in the network, H(X|R,C) is not minimized. Physiological realism may therefore require some modifications in application of coherent infomax.

Motor processes cannot be modeled by a single (unified) model. Instead, a number of models at different levels of description are needed. The concepts of control and control variable only make sense at the functional level. A clear distinction must be made between external models and internal models. General Systems Theory provides the framework for a proper treatment of these issues.

Phillips & Singer (P&S) extend ideas derived from the observation eight years ago that the coherence (synchronization) of cortical oscillations can be modulated by the structure of visual stimuli. As described in the target article, a large part of the continued interest in this finding is related to independent theoretical work suggesting that synchronized cell firing could help solve the problem of binding together within cortex neuronal activity associated with different attributes of visual stimuli. The authors present an abstract “proof of concept” model describing how their cortical processing scheme could work, but our biologicallyrealistic models of cortical relationships suggest that the proposal is biologically implausible. Our realistic models lead to a very different interpretation of the significance of cortical oscillations.

Several types of amygdala-dependent learning can be blocked by local infusion of NMDA antagonists into the amygdala. This blockade shows anatomical, pharmacological, temporal, and behavioral specificity, providing a pattern of data more consistent with a role for NMDA receptors in learning than in arousal or attention, and supporting the contention that an “LTP-like” process is a neural substrate for memory formation.

The strong coupling of binding to cross-correlations is methodologically problematic. A completely unstructured network of neurons can produce cross-correlations very similar to the measured ones, and yet they have little dynamic effect.

A fundamental assumption in Shors & Matzel's target article is that brain activity can be related to the traditional categories of mentalistic psychology. This has led them to make numerous further assumptions that are contradicted by the available evidence.

Gene targeting has generated a great deal of data on the molecular mechanisms of long-term potentiation and its potential role in learning and memory. However, the interpretation of some results has been questioned. Compensatory mechanisms and the contribution of genetic background may make it difficult to unequivocally prove the existence of a causal (genetic) link between LTP and learning.

Although one can endorse the complexity of the data and processes that Phillips & Singer (P&S) review, their mathematical suggestions can be compared critically with cases in nonlinear psychophysics, where the theoretician is faced with analogous problems. Owing to P&S's failure adequately to recognise both the intricate properties of nonlinear dynamics in networks and the constraints of metabolic demands on the temporal generation of patterns in biological nets their conclusions fail to meet the problems they properly address.

Eye movements play a variety of roles in perception, cognition, and communication. The roles are revealed by the duration of fixations reflecting the quality of processing in the first line. We describe possible roles of eye fixations in different temporal diapasons. These forms of processing may be specific to sensorimotor coordinations. Any generalization to other domains should be cautious.

Shors and Matzel's evaluation of approaches to the behavioural function of LTP is welcome, and should encourage a widening of conceptual approaches to this problem. In addition to their call for increased sophistication in thinking about LTP, there needs to be a parallel increase in sophistication in the study of behaviour. Changes in emotional state or tone may be a better function for LTP than attention mechanisms.

The basic concepts of motor control formulated in our target article were derived from specific experiments, a fact which is disregarded in Dalenoort's comments. A purely academic approach to motor control may not result in a clearer understanding of control concepts.

There is evidence for increase, followed by decline, in synaptic numbers during development. Dendrites do not function in isolation. A constructive neuronal process may underpin a selectionist cognitive process. The environment shapes both ontogeny and phylogeny. Phylogenetic natural selection and neural selection are compatible. Natural selection can yield both constructivist and selectionist solution to adaptuive problems.