Other times it feels more like your brain is reconstructing it from fragments.

I think that's what happens more often than not. It's certianly more efficient; instead of "recording" the grociery store every time you go, you just remember it once and reference that memory each time you go.

And that's also why "eyewitness testimony" is such a tricky thing to deal with; rarely do we remember every detail of every event--but when the memory suddenly has some importance (like when you're asked to testify) our minds try to fill in the gaps ... often inaccurately.

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I'm like one of those idiot savants...well, except for the savant part.
"In order to increase awareness of the homeless, security have been given binoculars."