9, I found solid foundation for my own thinking about learning. A reinforcer is any object or event that increases the probability of a response. Positive reinforcement takes place when a reward or pleasant event follows an action.
Negative reinforcement rewards a response by bringing an end to discomfort.
Primary reinforcers are natural physiological or biological rewards. Learned reinforcers are called secondary reinforcers. Delay of reinforcement reduces its impact. If the delay is long no learning at all will take place. Nevertheless, long chains of behavior may be reinforced by a single reward.