Time on the Brain: How You Are Always Living In the Past, and Other Quirks of Perception

Sep 23, 2011 Source: blogs.scientificamerican.com

I always knew we humans have a rather tenuous grip on the concept of time, but I never realized quite how tenuous it was until a couple of weeks ago, when I attended a conference on the nature of time organized by the Foundational Questions Institute. This meeting, even more than FQXi’s previous efforts, was a mashup of different disciplines: fundamental physics, philosophy, neuroscience, complexity theory. Crossing academic disciplines may be overrated, as physicist-blogger Sabine Hossenfelder has pointed out, but it sure is fun. Like Sabine, I spend my days thinking about planets, dark matter, black holes—they have become mundane to me. But brains—now there’s something exotic. So I sat rapt during the neuroscientists’ talks as they described how our minds perceive the past, present, and future. “Perceive” maybe isn’t strong enough a word: our minds construct the past, present, and future, and sometimes get it badly wrong.

Neuroscientist Kathleen McDermott of Washington University began by quoting famous memory researcher Endel Tulving, who called our ability to remember the past and to anticipate the future “mental time travel.” You don’t use the phrase “time travel” lightly in front of a group of physicists for whom the concept is not a convenient metaphor but a very real possibility. But when you hear about how our minds glide through time—and how our memory provides a link not only to the past but also to the future—you see Tulving’s point.

McDermott outlined the case of Patient K.C., who has even worse amnesia than the better-known H.M. on whom the film Memento was based. K.C. developed both retrograde and anterograde amnesia from a motorcycle crash in 1981. (The literature doesn’t say whether he was wearing a helmet, but let this be a lesson.) He can’t remember anything that happened more than a few minutes ago. He retains facts and skills, but can’t remember actually doing anything or being anywhere.

Tellingly, not only can he not recall the past, he can’t envision the future. When researchers ask him to picture himself somewhere he might go, he says that all he sees is “a big blankness.” Another patient McDermott has worked with can explain the future in the abstract, but says he can’t imagine himself in it.

To investigate the perception of past and future in people without brain injuries, McDermott did fMRI brain scans of 21 college students, asking them to recall a specific incident in their past and then envision themselves in a specific future scenario. Subjectively, the two feel very different. Yet the scans showed the same patterns of activity. Areas scattered all over the brain lit up; our temporal perception is distributed. As a control, McDermott also asked the students to remember events involving Bill Clinton (presumably, ones they were not personally involved in), and the patterns were very different. In a follow-up study, McDermott asked 27 students to anticipate an event in both a familiar and an unfamiliar place. The brain scan for the familiar one resembled the one for the act of remembering; the unfamiliar one was the odd man out.

The bottom line is that memory is essential to constructing scenarios for ourselves in the future. Anecdotal evidence backs this up. Our ability to project forward and to recollect the past both develop around age 5, and people who are good at remembering also report having vivid thoughts about the future.

McDermott’s colleague Henry Roediger studies metacognition—thinking about thinking. We express varying degrees of confidence in our memories. How we do this is clearly an issue for the court system. The N.J. Supreme Court recently tightened standards on the consideration of eyewitness testimony, citing the risk of false positives. Roediger pointed out that false negatives get less attention, but are equally bad. The worst eyewitnesses are full of passionate intensity, and the best lack all conviction. In both cases, innocent people can be sent to death row while the guilty walk.

Cognitive psychologists find that confidence sometimes correlates with accuracy, sometimes not. Roediger gave volunteers a memory word test. They had to study a list of words; afterwards, they were presented with a series of words and had to indicate whether each had been on the original list. They also had to say how confident they felt about their answer.

Whenever I hear about such tests, I brace myself for bad news. But Roediger said people actually did pretty well, and their confidence scores tracked the accuracy of their recall. Their blind spots were predictable. They systematically messed up, both in recall accuracy and self-assessment, when presented words that weren’t on the list but were synonyms of ones that were. The findings match what happens with eyewitnesses. We get things broadly right, but are easily confused by similar situations and faces.

It’s not that our memory is a glitchy wetware version of computer flash memory; it’s that the computer metaphor just doesn’t apply. Roediger said we store only bits and pieces of what happened—a smattering of impressions we weave together into feels like a seamless narrative. When we retrieve a memory, we also rewrite it, so that the time next we go to remember it, we don’t retrieve the original memory but the last one we recollected. So, each time we tell a story, we embellish it, while remaining genuinely convinced of the veracity of our memories.

So go easy on your friend who caught the 150-pound catfish. He wasn’t consciously lying, which is why he spoke with conviction, but that still doesn’t mean you should swallow his tale. To confuse is human; to accept we confuse, divine.

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