(Metzinger, 2003) characterizes attention as follows.
Attention "is a selection process, which episodically increases the capacity for information-processing in a certain partition of representational space. Functionally speaking, attention is internal resource allocation. Attention, as it were, is a representational type of zooming in, serving a local elevation of resolution and richness in detail within an overall representation."
In slightly more detail
"In short, attention is a process of subsymbolic resource allocation taking place within a representational system exhibiting phenomenal states. It is a form of non-conceptual metarepresentation operating on certain parts of the currently active, internal model of reality, the conscious model of the world. By guiding our attention towards a perceived object, we achieve a selection and an enhancement. By turning towards the phenomenal representation of this object, we automatically intensify the information processing in the brain, which underlies it. Simultaneously we increase our degree of alertness and orient towards the object in question. However, we do so without mentally forming a concept for this object. Typically the object becomes more salient in this act, it becomes richer in detail and more coherent by being segregated from a background at the same time – a new and better representation is generated. Within neuroscience, a popular assumption is that – strictly speaking – the object is first of all constituted through attention, because a number of single feature detectors are now functionally inte grated into a larger whole, a dynamically bound assembly. In this way, attention is a constructive form of representing another representation (or a set thereof) with the help of non-conceptual mental means, a subsymbolic kind of metarepresentation. Object perception never is a passively synthetic process, because many target stimuli can only be discovered after their elementary features have already bound into a whole. And this is another central function of attention: it identifies a certain characteristic combination of features within an ambiguous perceptual context. For example, visuo-spatial attention helps to segment a phenomenal scene and thereby contributes to a reduction of ambiguity."
"Within the representational architecture of the human mind, the guiding of attention is a supramodal capacity. For instance, attention can be shifted around independently of eye-movements, i.e. it can move within the visual field while the position of the eyes remain stable. Husserl frequently spoke of the lickstrahl, the ray of the glance. Another beautiful and classical phenomenological metaphor is that of describing visuo-spatial attention as a "cone of light." This meta phor is consistent with a functional analysis of attentional metarepresentation because objects in the cone of light of attention are processed in a better, faster, and deeper fashion. On the level of neuroscience we find that, for instance, spatial attention functionally penetrates early stages of visual information processing, by selectively inhibiting certain paths of processing, and enhancing others. Although there presently exists no comprehensive neuroscientific theory of attention, it is quite clear that it is a limited-capacity process, which can directly modulate the response profile of individual neurons and can be described neither as a property of any narrowly circumscribed anatomical region nor as a property of the brain as a whole. Our attention system is constituted by a large number of single and interacting networks, which can be specialized in a highly diverging manner."
"Attention generates non-conceptual content, for which frequently we possess no transtemporal identity criteria and which therefore is ineffable."
- Written in 2003.