Back in 2014, Inge Teblick made her first online course - in English ("kitchen English" as she calls it herself, pardon her heavy Flemish accent), after a well received lecture she gave at the Equine Clicker Conference in 2013. You may not know it, but she was one of the first ones to connect the dots on how autonomy, choice, and clicker training are and should be connected - and she came to these insights through... playing games.
Meanwhile concepts have been finetuned, theoretical ideas have been explored in practical settings, more research gave more depth to some of the basic ideas formulated in here, but this course was the first time she tried to bring a variety of concepts from motivational research and the emotional effects of practical training together.
This course has later been translated into a lot more in-depth courses in Dutch, all on this site, and split into the main topics you'll find touched on in here.
So here, for you: the old, first, original course on 'Theory of Fun'.