Which form of reinforcement occurs after an uncertain period of time?

The form of reinforcement that occurs after an uncertain period of time is known as variable interval reinforcement. This type of reinforcement schedule delivers rewards after varying lengths of time, making it unpredictable when the reinforcement will occur. Because the timing of the reinforcement is uncertain, it tends to maintain a high and steady rate of responding, as individuals are motivated to continue their behavior in anticipation of receiving a reward at some point.

In contrast, fixed interval reinforcement provides a reward after a specific amount of time has passed, creating predictable patterns in behavior—often leading to a "scalloping" effect where responses increase as the time for reinforcement approaches. Fixed ratio reinforcement, on the other hand, provides rewards after a certain number of responses have been made, which can lead to bursts of activity followed by pauses. Multiple reinforcement is not a standard term in reinforcement theory and does not specifically refer to a recognized schedule of reinforcement.

The unpredictable nature of variable interval reinforcement is key to its effectiveness in encouraging sustained behavior over time, as individuals remain engaged with the activity due to the possibility of a reward at any moment.