Final answer:
The aunt's increased likelihood to take aspirin in the future due to its pain-relieving effects demonstrates operant conditioning, particularly positive reinforcement.
Step-by-step explanation:
The student's aunt is demonstrating the concept of operant conditioning, where behaviour is influenced by the consequences that follow. When the aunt takes aspirin and experiences pain relief, this positive outcome reinforces the behaviour, making her more likely to take aspirin again in the future when she has a headache. This is a type of positive reinforcement, where the addition of a reinforcing stimulus following a behaviour makes it more likely that the behaviour will occur again.