Fleur has gleeful look when adults make weird sounds before doing something funny. Nose boops, tickles, and the like. She loves the stuff from people she likes. And doing it well, is a good way into her favorite people list.
Dopamine is thought of as the reward neurotransmitter. But, it is more complicated. It is what we get anticipating a reward. Say, you are playing a video game, dopamine surges to ensure you focus and persevere to achieve the level or match.
The noise right before tells her it is coming. Classical conditioning pairs a neutral stimulus with a desired one. The prior one is neutral the first time, but after she has paired it with the desired stimulus and anticipates the desired one. It seems like she enjoys the anticipation almost as much.
In getting mobile and manipulating objects, she is learning to use operant conditioning as well. She exerts her will on the world around her. This takes the form of doing the same thing over and over both using the same technique to confirm it works and adjusting to see what might work better. The other day she was trying to get into my tablet and tapping different spots to see how it reacted. You could see the Scientific Method in action: hypothesis, design test, execute test, evaluate result, new hypothesis.
Something I never thought about in university psychology classes was the impressive nature of linking things into causal chains. If this, then that. Over and over. Both forms of conditioning require understanding causation. The sponge that is Fleur’s brain seems to seek out understanding causation. And happiness to me is creating an environment for her try things and figure out how they work.