Could you explain how perception relates to the attentions?

Perception is relative, just like the big relativity thingy says.  The problem is we are locked, or most of us, are locked into a certain way of perceiving the world.  When something changes our position - whether it is our own energy pushing on us, or a change in circumstance we had no control over - we have to alter our perception to match a new reality.  Most of these shifts, hinkies, or bobbles are very close to our own reality and so we only notice a disturbance in the way we perceive it.  Sometimes those shifts can be radical and our perception is stunned by the movement and requires time to reassemble a new perception.  Hence, some small shift can really whack you depending on how fixed you are to start.  As shifts become actual movements toward another reality than this one altogether, we find it impossible to hold onto a cohesive sense of perception without the personal energy to do so.  The shift itself is very disorienting, or can be.

A shift occurs in perception within this reality.  A movement is an actual physical movement of your energy past this reality into another.  Once you are there you often find the same rules don't apply as they do here in this reality.  The physical symptoms vary, but in general the first thing that happens when you shift is disorientation, spatial lapses and the general feeling of being sucked either down or up, like being pulled physically through a soda straw.  The idea though, shamanically is to get as clean a slate as possible so your perception is as clear as it can possibly be within your own energy.

Are the movements linear, i.e.: progressive, like legs of a journey?

Not really. They tend to go where your intentions are aimed.  The idea is to gain better and better control of them so you can direct them in this way. We start out hopping.  We recoil at the change, but in time and if you're basically crazy they become more controlled, less disorienting and destinations become possible.  Movements are pretty drastic; shifts however can take you up to the point of movement and, in that sense, I suppose it is a linear process.