Skinner studied 4 types of situation. A pellet given: 1. Fixed Interval (FI) – e.g. once every minute 2. Variable Interval (VI) – e.g. after various intervals, averaging once a minute 3. Fixed Ratio (FR) – e.g. every 20 presses 4. Variable Ratio (VR) – e.g. after varying numbers of presses, averaging 20
