how do our eyes move ?

Imagine you’re watching a tennis match. Or better, imagine you’re the chair umpire. You must focus on the yellow ball, decide whether or not it is in and continuously follow its trajectory. At the end of the match, your eyes will “feel tired”. That’s because you made them work a lot while following the small yellow moving target. Which kind of movements do our eyes perform while tracking a moving object?

So, the situation is that the tennis ball moves quickly from one side of the court to the other and you want to continuously look at it. You have two possibilities: either you follow the ball by rigidly turning your whole body (or just your head) without changing the direction of your gaze, or you move just your eyes by performing really quick changes of direction. In the first case, you’d look quite weird and at the end of the match you’ll be completely sweat; in the second case, which is the solution we normally adopt in all similar daily life activities,  you’d properly employ your extraocular muscles in order to optimize the control of your eye movements.

When our eyes quickly jump from a position to another, they are performing the so-called saccades. To have an idea, pick the triangle and the star on the left (in the middle, the extraocular muscles are shown!) and jump with your eyes repeatedly from one to the other, as quick as possible: you’re just performing saccadic eye movements (video at the end of this post). Their maximum angular speed is proportional to their length (the distance they have to cover) and can attain up to 1000 deg/sec. A saccade takes 200 milliseconds to initiate and then lasts from 20 to 200 ms. This makes it the fastest movement produced by the human body, even faster than blinking (300-400 ms). Thanks to specific neuronal mechanisms connected to our eye muscles, time-consuming circuits are bypassed and everything works quite automatically (you don’t actually have to think about how to follow a moving object with your eyes, you just do that). All such amazing neuronal mechanisms are so natural and, in a sense, involuntary that saccades appear even in the opposite case, that is for fixational eye movements.

You, the chair umpire, are not sure whether the ball was in or out. Thus, you take the slow motion of the match and you stop the video on the exact instant when the ball touched the ground. Now you start staring at the still yellow target, which is still. After some seconds of prolonged visual fixation, some small, jerk-like, involuntary eye movements, similar to miniature versions of saccades, will occurr. They are called microsaccades and participate to the maintenance of visibility, even if their precise role in visual perception is is still largely unresolved.

Now imagine you’re watching the dvd of your favourite tennis match and you accidentally push the button that slows the video down . Instead of the real velocity, you’re watching the match at 0.2x speed. The ball has a really slow motion and you try to follow it with your eyes. You can perform smooth movements of your pupils, something that is completely different from the saccadic jumps you were obliged to during the match! This voluntary gaze shift to closely follow a moving object is allowed by smooth pursuit eye movements, which are asymmetric: for example, most humans and primates tend to be better at horizontal than vertical smooth pursuit.

Saccades and pursuits are just two of the main types of eye movements (you can find a complete list here).

sources: i, ii, iii, iv

Mind-controlled Helicopter

Awesome news!   🙂   (from this website)

University of Minnesota researchers have been able to control a small helicopter using only their minds, pushing the potential of a technology that could be used to help paralyzed or motion-impaired people interact with the world around them.

The controls for the mini-vehicle, which looks and flies much like any remote controlled helicopter, are otherwise fairly simple: if you want it to go up, think about it going up. If you want it to go down, think about it going down. There have been other brain controlled devices before, but the project created by Professor Bin He’s team offers extremely smooth control — and doesn’t require drilling holes in your head. “It’s completely non-invasive. Nobody has to have a chip implanted in their head!” said Brad Edelman, a graduate student working on the project.

The technology used is an electroencephalography (EEG) cap with 64 electrodes that fits over the head of the person controlling the helicopter. The researchers map the controller’s brain activity while they perform certain tasks (for example, making a fist or looking up). They then map those patterns to controls in the helicopter. If the researchers map “go up” to a clenched fist, the copter goes up. After that, the copter will go up automatically when the controller clenches a fist.

Of course, the brain patterns can be more subtle than fist clenching and the process can be trained so that no physical actions are necessary. Usually, to get even finer control over devices via brain power, the scientists need to dig deeper. Literally. With devices installed into the brain directly, fine motor control over things such as computer cursors is possible. However, the University of Minnesota test shows that this brain invasion may not be needed except in very specific cases. The control is precise enough take the helicopter through a relatively complex obstacle course.

Professor He, the team leader, feels that the non-invasive approach has a far broader appeal for people who don’t want people cutting into their skulls. “My entire career is to push for noninvasive 3-D brain-computer interfaces, or BCI,” He said in a release. “[Researchers elsewhere] have used a chip implanted into the brain’s motor cortex to drive movement of a cursor [across a screen] or a robotic arm. But here we have proof that a noninvasive BCI from a scalp EEG can do as well as an invasive chip.” For He, this distinction is important, because he sees it as the best way to popularize the technology. “The ultimate application really is to benefit disabled patients who cannot move or patients that suffer with movement disorders,” Prof He told the BBC. “We want to to control a wheelchair, and turn on the TV, and most importantly — this is my personal dream — to develop a technology to use the subject’s intention to control an artificial limb in that way, and make it as natural as possible.”

The technology isn’t just for people who have lost normal function in their bodies, Proffessor He also sees the technology as something that could “enhance function beyond what we can accomplish,” for everyday people. There are still some issues with the technology as it stands. The five subjects the researchers tested were only able to control the helicopter with about 90% accuracy. That’s high, but not perfect for tasks which need more precision. Additionally, there was a slight latency between the thought input and the copter reacting. “I think the potential for BCI is very broad,” He said in a release. “Next, we want to apply the flying robot technology to help disabled patients interact with the world. It may even help patients with conditions like stroke or Alzheimer’s disease. We’re now studying some stroke patients to see if it’ll help rewire brain circuits to bypass damaged areas.”

Chercheur en Robotique Médicale

Voici un clip-métier sur la profession de Chercheur en Robotique Médicale. La vidéo a été tournée au LIRMM en janvier dernier et est en ligne sur le site “100 métiers en Languedoc-Roussillon“, édité par l’ONISEP (Office National d’Information Sur les Enseignements et les Professions).

Reconnaissez-vous quelqu’un dans cette vidéo? 😉