Here are 2 fantastic informative videos by Kurt Leland. I have watched the first one many times because there is no much good information to be found in it that you really can't "digest" it all at once. Also, I found that some of didn't make sense to me, until I developed further myself.
The second one is very good as well and I guess I will be watching that a few more times too, lol.
https://www.youtube.com/watch?v=uA12Xd3Zq0I
https://www.youtube.com/watch?v=hYkjaqfOvvo
Here is Kurt's website for anyone who wishes to learn more about him and his research.
http://www.kurtleland.com/
Kurt is a knowledgeable person and I'll recommend watching these vids.
Most of us could learn from how things are put across.
Thanks Lumaza.