Casting the actors in your head
When I read fiction, it's kind of like watching a film in my head through a murky window - the events play out in my mind's eye, but not with absolute clarity, though the voices are usually distinct. Often I'll end up with a real actor playing the character, either because the physical description put me in mind of them, or because they've played a similar character in something I've seen. Jack Shaftoe in Neal Stephenson's Baroque trilogy, for instance, is for whatever reason played by a young James Bolam.
Where I've seen a TV or film adaptation, the casting for the version in my head is more straightforward. Both Marlowe and Spade are forever Bogart thanks to The Big Sleep and The Maltese Falcon, I probably saw those films before I started reading either Chandler or Hammett. Hercule Poirot can't be anyone other than David Suchet, again the TV adaptation might have just come to my notice before the books did. Maigret is a trickier one, however. I can no longer remember how I pictured Maigret, or how he spoke, when my dad first introduced me to a shelf of Simenon, but ever since we watched the TV adaptation in the early 90s, Maigret has been Michael Gambon whenever I've read the books. It's with mixed feelings, therefore, that I read of Rowan Atkinson's role as Inspector Maigret in two new TV films - I'm sure he'll be good, I just don't want to muddy the Gambonesque waters.
Interestingly (at least to me), OneMonkey doesn't always read aloud/hear character voices in his head when he's reading a book. Nor does he always picture the events being described. Naturally I assume I'm the normal one and he's odd, but it would be fascinating to find out how other people read (as OneMonkey says, long descriptions of how a room looks are often wasted on him - as a writer am I generally wasting my time on that sort of thing or do most people get something from it?). Feel free to comment here and let me know.