Homeostasis is literally maintaining normal body function. For example, sweating because you are hot, to maintain the right body temperature(which is a body function)c is maintaining homeostasis.
The variable is the group that was given caffine, because thats what the doctors manipulated. They possibly altered the natural memory of the participants by giving them caffine. A more specific variable could be how much caffine each participant is given and what time are they given it.
A small community seems to be the best answer
You didn't put the answers