 Hi, my name is Sebastia Matau. I work for the CNRS at Ex Marseille University in France and today I would like to show you a technique that we have developed to essentially write text, write letters, by thinking of letters. Now I will demonstrate this technique in a minute and what you will see is that there are a bunch of letters on the screen in a circle and without moving any part of my body, even without moving my eyes, I will covertly attend to one of these letters. So, and covertly attending means that I will pay attention to it from the corner of my eye, right? So without making any kind of eye movement and the computer using a very clever technique that I will explain at the end of this video will decide which of the letters I am attending to and will select that letter for me and in this way I can write letters simply by paying attention to letters without making any kind of movement. Now, let's see how this works. The text that I'm going to write is the word hello and it will take a while So we will play it back in we will fast-forward a little bit. So it is slow, but it works really well. So how does this technique work? Well, the key thing is this little device right here which records the size of your pupil, black circle in the center of your eye. Now as you might know if you look at something that is bright your pupil becomes very small and if you look at something that is large your pupil becomes big, right? That's called the pupil every light response or pupil every light reflex and what we have found out previously in other studies and other people have also found out is that if you covertly, so from the corner of your eye, attend to something that is dark your pupil also becomes a little bit bigger and if you covertly attend to something that is bright your pupil also becomes a little bit smaller. So what we're doing here is we present the letters on a background that goes from bright to dark to bright to dark. And if I attend to one of these letters my pupil will sort of oscillate along with the brightness of this letter, right? So whenever the letter is on a bright background my pupil will be a little bit small and whenever the letter is on a dark background my pupil will be a little bit large and we can measure that using this pupilometer and based on that signal based on these very small changes in pupil size we can decode we can figure out which of the letters I am attending to and which of the letters I therefore want to select. So that's all. We just use very small fluctuations in the size of the pupil to figure out what is going on in your mind's eye when you're trying to write these letters. That's it. Thank you very much.