14 Beginner Expert Movies courtesy B Ölveczky Meet Andre. He’s a beginner at tennis, which maybe you can tell from his BLATANT footfaults and awkward form. Here we tracked his right hand as he tries to repeat the same exact service motion. Note there’s considerable difference between his hand motion in these consecutive attemptsWhen we plot 5 consecutive serves, the trial to trial variability is even more apparent.If Andre practices really hard over the next 10 years, he might stop foot faulting, and even eventually get to the level of Alexei, the top player on Harvard’s Varsity team. Alexei has an amazing serve, that clocks above 100 mph, and consistently hits the same corner of the service box. Alexei has beautiful form, and I want you to look at the remarkable consistency of his service motion. When we plot 5 of his serves, we can see that they’re nearly identical.I’m using this example to demonstrate a typical pattern in motor learning where performance increases, while variability decreases.One way of interpreting this pattern is that variability and performance are intrinsically inversely related: that reducing variability allows for increasing performance. Thus, variability stands in the way of performance, so in order to achieve high performance, the brain must learn to minimize variability. This is in line with the idea that optimal control strategies are often formulated with motor variability as a part of the cost function.But a different way of looking at this relationship, is that high variability precedes good performance. This is in line with the idea from Reinforcement learning: that high performance results from exploration which requires highly variable actions. Thus, highly variable movements allows for more extensive exploration, which promotes a faster search in movement space to find a motor solution.This second view has been extensively studied in the birdsong model system. Male songbirds spend their lives learning and maintaining a mating song. Decades of work have revealed the brain circuit responsible for song learning. Evidence suggests that the songbird brain purposefully generates and regulates song variability in order to facilitate learning and performance in different respective contexts. [refer to diagram] When the juvenile bird is first learning its song, consecutive renditions are highly variable. Interestingly, this variability is driven by a specific brain region, referred to as LMAN. If LMAN is lesioned in a juvenile bird, the song variability is dramatically decreased, and further improvement of that song is halted. This suggests that motor variability is actively generated in the brain, and that it is required for learning.Here we’re going to explore the idea that motor variability drives motor learning in humans. And that differences in motor variability from one person to another --measured before any training has occurred—predict person to person differences in learning ability.
15 Redeneren: omgaan met onbetrouwbare signalen kennisPerceptiezintuigen
22 Ook Rafael van de Vaart sprak zich uit over de bal: "Niet normaal hoe die bal zwabbert. Daar kun je echt niet aan wennen", aldus Van der Vaart. Iker Casillas, de doelman van Spanje, ging zelfs zo ver de bal een 'strandbal' te noemen.