Yeah, I actually laughed when the experimenter told me to do that because he just said it so matter-of-factly. "Ho hum, tie your shoes, snap your fingers, clear your mind of all thoughts." They know it's not trivial of course, but I guess there's not much more you can say. And even if you fail to keep your mind free of thoughts, just trying to do so is likely to produce a less noisy brain image than if you're letting your mind roam free.
They didn't really specify. I suppose they're content going with colloquial interpretations, which I don't think is bad-- intuitively, there's an identifiable feeling of being aroused and one of feeling 'bad' (I don't know if that's exactly how they phrased it, but it was something simple), and they're pretty clearly distinct.
Not really, but it sounds like it might have something to do with attributing emotions to aroused states. (e.g. experiments have shown that people who are played a recording of a rapid heart beat and told that it is a recording of their own heart tend to feel anxious as a result.) Maybe post something about it over in the Mind & Brain Sciences forum?
Yes, there's the pause to record assessments of arousal and affect, then there's another brief pause with a fixation point, and finally the time you spend looking at the cue. Altogether I'd say there was about 5 or 6 seconds inbetween actually viewing images. On some trials they also presented a cue without showing an image afterwards and then asked for arousal/affect ratings before repeating the cuing process.