The correct answer is fixed-interval
In a fixed interval reinforcement scheme, the reinforcement is presented if the organism emits at least one response after a fixed time interval. Generally, this scheme is represented, placing the specific value of the fixed interval. For example: FI-1 hour means that the backup is presented after 1 hour and only for the first response issued.
The fixed interval reinforcement scheme results in a low frequency of responses at the beginning of the interval, increasing as the end of the interval approaches.
