Learning is a relatively permanent change in behavior or knowledge due to experience. Behavioral changes can be due to learning or other causes like drugs, injury, or maturation. Learning starts with the mind accepting new knowledge which may or may not result in observable behavior changes. There are two main types of learning: classical conditioning where a neutral stimulus becomes associated with an original stimulus and response, and operant conditioning where people learn through reinforcement of pleasurable or avoidance of unpleasurable outcomes from behaviors. Perception involves how people interpret and make sense of their environment and is influenced by their experiences, motives, personality, and situational factors.