What type of reinforcement schedule provides the least predictability for the subject?

The variable ratio reinforcement schedule is characterized by providing rewards after an unpredictable number of responses. This unpredictability means that the subject cannot anticipate when the next reward will come, which tends to create a high and steady rate of responding, as the subject continues to engage in behavior in hopes of receiving a reinforcement.

In the context of reinforcement schedules, the variable ratio schedule is known to be the most effective for maintaining behavior over time because it keeps the subject engaged without allowing them to form a predictable pattern. For example, this schedule is commonly seen in gambling scenarios, where a player may win after an unknown number of plays, thus reinforcing the behavior of playing.

In contrast, fixed schedules (both fixed interval and fixed ratio) provide a set pattern or predictability regarding when responses will be reinforced, leading to more predictable behavior from the subject. Continuous reinforcement is also highly predictable, as every single occurrence of the desired behavior results in reinforcement. Therefore, the variable ratio schedule provides the least predictability, fostering a high level of response due to the uncertainty involved.