When I explore attention, I find that it lives its own life as anything else, and on its own schedule. It is of course influenced and triggered by perception (for instance something unexpected arising) and stories (directing it), but that too lives its own life and happens on its own.
I also find that it can be more narrowly focused or more widely embracing, although it can always go to what was previously in the periphery of attention.
And I see that attention is content of awareness. It comes and goes, moves around, is more narrow or more broad, and so on. In pure awareness without content, there is no attention because there is nothing to attend to, and also no attention since that too is content of awareness. This is also why it lives its own life, on its own schedule, and with infinite causes and infinite effects as anything else.
Attention also seems to be related to the different sensory fields in different ways.
For instance, it is related to the vision field in several ways.
First, the obvious one in that what the eyes focus on is often, but not always, where attention is as well. Sometimes, the eyes focus somewhere, and attention is on something else in the visual field or in another sensory field. Or it can of course be in a particular sensory field without the aid of visual input through the eyes.
From here, I find that when attention is on sensation, it is guided by imagined images, by visual thoughts. For instance, there is a focus of attention on sensations in my right ankle, and this focus is guided by a body image in the thought field. This body image filters out sensations into ankle, or a center, and not-ankle as periphery.
The same is even true for sound. Right now, there is the humming of the fridge, and if attention goes to that humming, it is aided by an image of a fridge (and also an image of the quality of the sound) to help filter out fridge and non-fridge sounds. This one is more mixed as attention is also guided and filtered by thought remembering the sound as it was, creating a sense of continuity, and this is a sound thought (a thought mimicking the sound field) rather than an image thought.
So when attention is focused within a particular sensory field, it seems often guided by a visual thought (imagined images), and also a thought mimicking that same field (a sensory, sound, taste, smell thought, or imagined sensation, sound, taste and smell). If nothing else, the visual though helps spread the perceptions out in space, so it becomes easier to differentiate them and filter out a subset of them.
More generally, it seems that attention is, independent of anything else, an image thought placed on top of perception, almost like a bulls eye or a boundary determining what within perceptions arising is inside and outside.
And as such, attention too is somewhat of an illusion, a gestalt arising from believing in a thought.