Which situation represents a Variable Interval Schedule?

A Variable Interval Schedule is characterized by providing reinforcement after an unpredictable amount of time has passed. This schedule creates a scenario where the subject cannot predict exactly when the reinforcement will come, which tends to maintain a consistent behavior over time as the individual continues the desired action without knowing when the reward will be given.

In this case, earning $1 after an average of 60 minutes of practice fits this description well. Jacob does not receive the dollar after a set time, but rather after an average time interval. This means that sometimes he might earn the reward sooner than 60 minutes and at other times it might take longer, reflecting the variability and uncertainty typical of a Variable Interval Schedule.

The other options present different contingencies of reinforcement. Receiving a fixed reward for a specific amount of practice time or a set number of songs practiced indicates a Fixed Interval or a Fixed Ratio schedule, where the time or count is predictable. Consistently earning $1 regardless of time remains constant and thus does not involve any interval-based requirements.