Final answer:
The improvement of Julie's dance skills during recitals is an example of social facilitation, where the presence of others enhances performance on familiar tasks.
Step-by-step explanation:
Julie's improvement during recitals compared to her dance practice at home demonstrates social facilitation. This psychological phenomenon, first studied by Robert Zajonc, suggests that performance can improve on well-practiced tasks when in the presence of others.
This happens because the presence of others can increase arousal, which enhances the execution of tasks that are familiar or simple for the individual. In Julie's case, her dance skills are better during recitals because she is likely experiencing this heightened state of arousal that aids in performing tasks she is already good at.