Intermittent reinforcement is the delivery of a reward at irregular intervals, a method that has been determined to yield the greatest effort from the subject. The subject does not receive a reward each time they perform a desired behavior or according to any regular schedule but at seemingly random intervals.
Reinforcement theory is an area of behavioral psychology that explores the ways that people and other animals respond to rewards delivered according to various schedules. Rewards may be delivered continuously, at regular or irregular intervals. In rat studies, researchers found that the way to keep the subjects working longest was to reinforce the behavior at unpredictable intervals, rather than regularly.
Intermittent reinforcement and other principles of reinforcement theory are applied in areas of technology and business including human resource management, marketing and machine learning. In designing mobile apps and social media, intermittent reinforcement might take the form of rewards delivered on a schedule that seems random to the users but is designed to keep them active for longer. For example, "likes" might be reported when an algorithm has determined that the user is likely to leave Instagram. Through its algorithms, Facebook can detect when a teenager is likely to feel insecure and deliver a confidence boost.
Online gambling and internet addictions exhibit the same principle: The individual receives just enough rewards (which might be in the form of wins or entertainment) at sufficiently sustainable intervals, to encourage them to continue.
See also: brain hijacking