WEBVTT 00:00:06.151 --> 00:00:08.266 Have you experienced déjà vu? 00:00:08.290 --> 00:00:12.540 It's that shadowy feeling you get when a situation seems familiar. 00:00:12.564 --> 00:00:15.527 A scene in a restaurant plays out exactly as you remember. 00:00:15.551 --> 00:00:18.335 The world moves like a ballet you've choreographed, 00:00:18.359 --> 00:00:20.836 but the sequence can't be based on a past experience 00:00:20.860 --> 00:00:23.376 because you've never eaten here before. 00:00:23.400 --> 00:00:25.305 This is the first time you've had clams, 00:00:25.329 --> 00:00:26.737 so what's going on? 00:00:26.761 --> 00:00:30.462 Unfortunately, there isn't one single explanation for déjà vu. 00:00:30.486 --> 00:00:33.112 The experience is brief and occurs without notice, 00:00:33.136 --> 00:00:36.686 making it nearly impossible for scientists to record and study it. 00:00:36.710 --> 00:00:40.069 Scientists can't simply sit around and wait for it to happen to them -- 00:00:40.093 --> 00:00:41.199 this could take years. 00:00:41.223 --> 00:00:43.341 It has no physical manifestations 00:00:43.365 --> 00:00:44.553 and in studies, 00:00:44.577 --> 00:00:47.543 it's described by the subject as a sensation or feeling. 00:00:47.567 --> 00:00:49.389 Because of this lack of hard evidence, 00:00:49.413 --> 00:00:52.382 there's been a surplus of speculation over the years. 00:00:52.406 --> 00:00:54.724 Since Emile Boirac introduced déjà vu 00:00:54.748 --> 00:00:57.059 as a French term meaning "already seen," 00:00:57.083 --> 00:01:00.441 more than 40 theories attempt to explain this phenomenon. 00:01:00.465 --> 00:01:04.738 Still, recent advancements in neuroimaging and cognitive psychology 00:01:04.762 --> 00:01:06.641 narrow down the field of prospects. 00:01:06.665 --> 00:01:09.704 Let's walk through three of today's more prevalent theories, 00:01:09.728 --> 00:01:11.806 using the same restaurant setting for each. 00:01:11.830 --> 00:01:13.734 First up is dual processing. 00:01:13.758 --> 00:01:14.762 We'll need an action. 00:01:14.786 --> 00:01:17.371 Let's go with a waiter dropping a tray of dishes. 00:01:17.395 --> 00:01:18.587 As the scene unfolds, 00:01:18.611 --> 00:01:21.691 your brain's hemispheres process a flurry of information: 00:01:21.715 --> 00:01:23.207 the waiter's flailing arms, 00:01:23.231 --> 00:01:24.249 his cry for help, 00:01:24.273 --> 00:01:25.751 the smell of pasta. 00:01:25.775 --> 00:01:28.870 Within milliseconds, this information zips through pathways 00:01:28.894 --> 00:01:31.289 and is processed into a single moment. 00:01:31.313 --> 00:01:33.866 Most of the time, everything is recorded in-sync. 00:01:33.890 --> 00:01:35.250 However, this theory asserts 00:01:35.274 --> 00:01:37.996 that déjà vu occurs when there's a slight delay 00:01:38.020 --> 00:01:40.297 in information from one of these pathways. 00:01:40.321 --> 00:01:41.798 The difference in arrival times 00:01:41.822 --> 00:01:44.179 causes the brain to interpret the late information 00:01:44.203 --> 00:01:45.742 as a separate event. 00:01:45.766 --> 00:01:48.018 When it plays over the already-recorded moment, 00:01:48.042 --> 00:01:49.759 it feels as if it's happened before 00:01:49.783 --> 00:01:51.980 because, in a sense, it has. 00:01:52.908 --> 00:01:55.349 Our next theory deals with a confusion of the past 00:01:55.373 --> 00:01:57.403 rather than a mistake in the present. 00:01:57.427 --> 00:01:59.237 This is the hologram theory, 00:01:59.261 --> 00:02:01.530 and we'll use that tablecloth to examine it. 00:02:02.070 --> 00:02:03.348 As you scan its squares, 00:02:03.372 --> 00:02:06.267 a distant memory swims up from deep within your brain. 00:02:06.291 --> 00:02:07.487 According to the theory, 00:02:07.511 --> 00:02:09.202 this is because memories are stored 00:02:09.226 --> 00:02:10.604 in the form of holograms, 00:02:10.628 --> 00:02:11.719 and in holograms, 00:02:11.743 --> 00:02:14.200 you only need one fragment to see the whole picture. 00:02:14.224 --> 00:02:17.252 Your brain has identified the tablecloth with one from the past, 00:02:17.276 --> 00:02:18.991 maybe from your grandmother's house. 00:02:19.015 --> 00:02:22.837 However, instead of remembering that you've seen it at your grandmother's, 00:02:22.861 --> 00:02:24.830 your brain has summoned up the old memory 00:02:24.854 --> 00:02:26.448 without identifying it. 00:02:26.472 --> 00:02:29.796 This leaves you stuck with familiarity, but no recollection. 00:02:29.820 --> 00:02:31.968 Although you've never been in this restaurant, 00:02:31.992 --> 00:02:35.306 you've seen that tablecloth but are just failing to identify it. 00:02:35.330 --> 00:02:36.601 Now, look at this fork. 00:02:36.625 --> 00:02:38.015 Are you paying attention? 00:02:38.039 --> 00:02:40.144 Our last theory is divided attention, 00:02:40.168 --> 00:02:41.988 and it states that déjà vu occurs 00:02:42.012 --> 00:02:44.430 when our brain subliminally takes in an environment 00:02:44.454 --> 00:02:47.180 while we're distracted by one particular object. 00:02:47.204 --> 00:02:48.490 When our attention returns, 00:02:48.514 --> 00:02:50.324 we feel as if we've been here before. 00:02:50.348 --> 00:02:52.452 For example, just now you focused on the fork 00:02:52.476 --> 00:02:55.112 and didn't observe the tablecloth or the falling waiter. 00:02:55.136 --> 00:02:57.430 Although your brain has been recording everything 00:02:57.454 --> 00:02:58.694 in your peripheral vision, 00:02:58.718 --> 00:03:00.933 it's been doing so below conscious awareness. 00:03:00.957 --> 00:03:03.300 When you finally pull yourself away from the fork, 00:03:03.324 --> 00:03:05.707 you think you've been here before because you have, 00:03:05.731 --> 00:03:07.355 you just weren't paying attention. 00:03:07.379 --> 00:03:10.729 While all three of these theories share the common features of déjà vu, 00:03:10.753 --> 00:03:13.005 none of them propose to be the conclusive source 00:03:13.029 --> 00:03:14.142 of the phenomenon. 00:03:14.166 --> 00:03:16.546 Still, while we wait for researchers and inventers 00:03:16.570 --> 00:03:19.348 to come up with new ways to capture this fleeting moment, 00:03:19.372 --> 00:03:21.403 we can study the moment ourselves. 00:03:21.998 --> 00:03:25.480 After all, most studies of déjà vu are based on first-hand accounts, 00:03:25.504 --> 00:03:27.319 so why can't one be yours? 00:03:27.343 --> 00:03:30.703 The next time you get déjà vu, take a moment to think about it. 00:03:30.727 --> 00:03:32.114 Have you been distracted? 00:03:32.138 --> 00:03:34.235 Is there a familiar object somewhere? 00:03:34.259 --> 00:03:36.314 Is your brain just acting slow? 00:03:36.338 --> 00:03:38.600 Or is it something else?