When people learn something while in one state (e. g., when they are feeling joyful or sad), they are better able to recall that thing while in the same state. this is known as?

The correct answer is state-dependent memory

State-dependent memory refers to the phenomenon wherein people are able to efficiently retrieve memories if they are in the same psychological state as they were when the memory was first formed. An example of state-dependent memory is recalling information readily during an exam because you are caffeinated during it, just like you were caffeinated when you studied and first formed memories of the information. 

It allowed for things to be produced much more quickly and efficiently