There are some ways to test it though. For the past 15 minutes I've been taking "photographs" of people in this coffeeshop in my mind, closing my eyes, and trying to read details from that photograph. I take in a lot of detail but part of it is reconstructed. Like I remembered the guy had a green trilby hat, and my brain did a Google Image Search for "green trilby" and pasted it on the guy. When I opened my eyes, I saw it was actually a green plaid trilby. But in my mind's eye the image was realistic, even though I obviously hadn't truly seen it.