Frequency in EEG can be used as a decent correlate of neural attention, with different wave-type indicating degree of focus under different waking conditions.

Wiki explanations are here: http://en.wikipedia.org/wiki/Alpha_wave#Brain_waves

There is lot of literature describing attention mechanisms and networks in the brain. Most important structures involved in selective voluntary attention are the posterior parietal cortex, thalamus and prefrontal cortex. See for example books of David la Berge (1995) and Nelson Cowan (1996) for overviews. In addition, Event-Related Potentials (ERPs) are considered to be more specific indicators of selective attention to environmental stimuli than frequency shifts in the EEG.

Within the context of the Fractal Catalytic model the brain is treated as a catalyst utilizing the same fundamental principles to mediate transitions as may be observed at the level of the enzyme. At the scale of the enzyme transitions are effected via 'fixed points' ,or points of invariance shared by the 'before' and 'after' states. Thus, our eyes are drawn to the center of a spinning wheel because the axis represents a convenient fixed point by which the transitions of the spinning wheel may be successfully mediated. Fixed points may not always be literal points, we may choose to mediate a potential cognitive scene around the colour green, for example. Also, in certain circumstances, the potential cognitive scene may be mediated around a complex of related fixed points - this being dependent upon the intelligence of the observer.

I suggest that the attention corresponds to the process by which an observer may 'elect' from a variety of 'fixed points' those most appropriate to the problem or interest at hand. Thus, we may choose to mediate a potential cognitive scene around the colour green or blue depending upon what we are interested in.

The attention is a phenomenon difficult to analyse because it is often misunderstood. Although fixed points are central to the 'attention' and cognitive processes generally, the fixed points themselves do not always correlate directly with the object OF attention. Thus, although our observation of the entire spinning wheel depends upon transitions being mediated around the axis, the axis of the wheel is not necessarily the 'object' of interest.

Because of the relatively simple topological mapping between the retina and the visual cortex, I suggest that transitions are mediated via ensembles of neural activity shared by the before and after states of transitions.

Davia, C.J (June 2006), "Life, Catalysis and Excitable Media: A Dynamic Systems Approach to Metabolism and Cognition", in Tuszynski, J.A, The Emerging Physics of Consciousness (The Frontiers Collection), Springer, pp. 255–292, ISBN 978-3540238904