Procedural memory refers to the knowledge of certain activities or procedures, which eventually become automatic with repetition and practice. This type of memory is often used without conscious thought or planning, and is therefore very difficult to verbalize. Often, the best way to effectively explain procedural memory is by performing a particular task or action. Examples of such memories include knowing how to ride a bike, how to swim, or how to play a musical instrument.
The type of knowledge gained as a procedural memory tends to last for a long time. For example, once a person has learned how to ride a bike, he or she may not ride a bike for many years but the memory will instantly return the moment bike riding is attempted. Most procedural skills are therefore considered long-term procedural memories.
Declarative memory is distinct from procedural memory because it refers to fact-based memory, and it is easily verbalized. Due to the fact that it is more language-based than procedural memory, declarative memory is also more easily forgotten unless it is consistently used. There are two basic subtypes of declarative memory: semantic and episodic.
Semantic memory is related to the understanding of meanings or concepts, and is generally not personally relevant. An example of this is the understanding that a pen is a tool used for writing. Episodic memory is more personal based, and involves the recollection of events from an autobiographical perspective.
Procedural learning appears to be affected by damage to particular areas of the brain, such as the cerebellum and basal ganglia. By examining people with brain injuries, researchers have demonstrated that procedural and declarative memory formation appear to be controlled by different parts of the brain. Studies have also shown that these memory systems can function independently of each other.
An example of the way in which procedural and declarative systems function independently is the case of a brain-injured patient who is consistently trained to learn a specific task, and can recall the details of his or her training, but fails to improve at the task. This is an example of a damaged procedural memory but a functioning declarative memory. On the other hand, a patient with a functioning procedural memory but a damaged declarative memory would not recall the task training, but would display improved performance of the particular task.
Some schools of thought believe that procedural memories form a person's character. The basis of this way of thinking is that by learning certain behaviors or emotional responses, they become automatic responses to specific situations. This can be positive in the case of good habits, but it can also mean that negative behaviors are very resistant to change. From this point of view, it takes significant conscious effort to practice and relearn a new positive behavior until the negative one has been replaced.