WHERE HAVE THE HEARTS (FUN) GONE?
I was so frustrated by the heart system. I felt like I was continually being slapped for getting things wrong continuously, even though I was doing great! I am now on the new system, and find it BORING and repetitive. Can't there be some in between system where there are rewards without the frustration that the hearts gave. Don't have the same incentive that I had previously, and I am an avid Duollingo fan.
http://david-hu.com/2011/11/02/how-khan-academy-is-using-machine-learning-to-assess-student-mastery.html This is a blog which explains why Khanacademy.org moved away from streaks, which was a mechanism somewhat similar to Duolingo's hearts. Now both Khanacademy and Duolingo use a bar.
1) The bar is a more flexible indicator. They can mess with the exact method how to deduce or add to it without changing the UI. 2) It is more fair. With hearts you could finish a lesson without learning the topic well because you were just lucky. Or fail because you were unlucky. With bar, they can iterate on the grading method (as per point 1) and improve it.