Thanks to Brilliant for supporting  this episode of SciShow.

Go to Brilliant.org/SciShow to learn how you can  take your STEM skills to the next level! [♪ INTRO] There’s always a scene in  crime TV shows where a good guy detective brings a suspect to  the station for interrogation. The detective isn’t getting  anywhere until finally, he spots it.

The suspect looked to the right when  they answered their last question, a telltale sign that someone was lying. We got them, case closed, roll the credits. But in the real world, that detective may have arrested a completely innocent  person for just thinking.

When you answer a question, and you look  right, or left, or any direction really, that doesn’t mean you’re lying! Your eyes  do that all the time regardless of the question you’re answering. And it makes sense.

Looking at  something or someone while answering a question can make it harder to think, so  you might look away from what’s in front of you to ponder an answer.   But scientists have observed that we don’t  look away just to avoid distractions; even if you’re alone or have your  eyes closed, they keep moving. In fact, rapid, involuntary  eye movements, called saccades, continue for as long as you’re thinking,  and why that happens is linked to what you’re thinking about specifically. For example, if you’re doing a lot of  visual thinking, like a brain teaser, remembering a picture, or moving an item  in your head, your brain might treat that as if you were actually looking  at or moving that object.

What’s more impressive is that while  you’re holding that mental picture, your eyes will move in the  exact same pattern as the first time you looked at  whatever you’re imagining! And it’s not that you remember how your eyes moved the first time you saw the object. The same saccade pattern will still happen  if what you’re imagining came from a verbal description instead of actually seeing it.

By studying these eye movements,  scientists can determine which strategies people use during problem-solving  and what stage they’re on. For example, if you were to figure  out if two images mirror each other, you’ll need to imagine the shapes and rotate them in your mind to picture  them from different angles. And the way you tend to move  your eyes while doing this can suggest that you typically  break the shape down into smaller chunks and then  rotate each one individually.

But with visual thinking, it’s hard to  sort out which eye movements are due to visual processing, and which ones  might be due to just, well, thinking. Because our eyes don’t just move when  we’re thinking about visual problems. They move even more when we answer  verbal-based questions like, “do you remember what you wore yesterday?” Researchers think that that’s because  our eyes move when we’re searching our long-term memory, which happens  more often with verbal questions because we need to remember  things from different times, and all that recalling involves eye movements.

In fact, there’s some evidence that your  eyes move to different places when you’re thinking about the past, present, or future. So, in the same way that your eyes search  through visual space, where each eye position corresponds to a point in space,  your eyes might be searching through time, with each eye position corresponding  to a different point on a timeline. Although it’s still unclear whether eye  movements are necessary for non-visual thinking, or if they just happen at the same time.

Like, there’s some evidence that  intentionally making large eye movements back and forth might help memory recall,  but most of the unconscious saccades we make while thinking are really small. Not to mention that intentionally  suppressing eye movements doesn’t seem to make a difference in memory recall. So research on whether saccades actually serve a function while thinking is mixed.

But some scientists think that these  non-visual-related eye movements might be an artifact of how our brain evolved.  So the circuits used to search long-term memory evolved from the ones  used to search visual space. That would mean those eye movements we  make while thinking are vestigial, a remnant of an earlier stage in the  evolutionary process, and we don’t technically need it to search our memory. And while this phenomenon has been  studied for more than 50 years, it’s also been the fuel for some myths.

Like, remember that idea that you can  be a human lie detector if you see someone looking to the right? There’s  pretty much no evidence to support that. In fact, there’s not much  evidence that the direction our eyes move while thinking  means anything at all.

So, unfortunately, those  detectives are going to have to do a little more work to  figure out who the killer is. But if they want to know what  their suspect was thinking, they can always call CS…eye. Or you know, they can work  on their logic skills with Brilliant, the sponsor of today’s episode.

They’re an online learning platform with courses about science, engineering,  computer science, and math. They have recently revamped their Logic  course to be even more interactive. In there you can be like Sherlock Holmes  and solve challenging puzzles with only limited information.

And as  Holmes says, when you’ve eliminated the impossible whatever remains must be the truth! So if you'd like to hone your detective and  logic skills visit brilliant.org/scishow or click the link in the description. The first  200 people will get 20% off Brilliant's annual premium subscription, and checking  them out also helps us, so thank you! [♪ OUTRO]