I imagine it's the same for other writers - though strangely, I've never heard anyone else say this - but when I'm involved in a project, a novel especially, and really knowing where I'm going with it, everything else in the outside world seems to cohere. I will keep coming across things that support my theme - comments on the radio, incidents in the newspaper, threads on the web, and even things I hear people saying in queues. I guess what's actually happening is that I'm suddenly seeing and hearing the whole world through the focus of the novel, filtering out those things that don't fit and subconsciously homing in on those that do, but the experience of it is a really magical one, a feeling that your novel is being 'gifted' to you by the world.
But then there are those other things, mainly images, which strike you deeply while you're writing a novel, but don't actually feed into the novel itself: they become instead indelibly associated with the process and/or the period in which you write the novel. For instance, Too Many Magpies will always be associated in my mind with a particularly horrible M&S jumper someone bought me - maroon fair-isle and shapeless: it made me look barrel-chested - because I was wearing it one day when someone interrupted my writing at a very crucial moment, to bring me some manuscripts to read. When I was embarking on the rejig of my current novel a few weeks ago, and having to think really hard about how to do it - and spending very long hours at the desk each day - I decided I'd go out for a short run/walk first thing each morning to get at least some exercise and clear my head for the day. I didn't keep it up - I'm now so into the novel I want to get to it straight away in the mornings - but the first excitable but scary creative searchings involved in writing this draft are now associated in my mind with the park I walked in then, and a carpet of fallen red camellia flowers, and, as I stopped to look at it, the odd scratching, shuffling sound I heard to my side, which turned out to be the squirrel above eating a nut.