As compared with declarative memory, it is governed by different mechanisms and different brain circuits. Procedural memory is often not easily verbalized, but can be used without consciously thinking about it; procedural memory can reflect simple stimulus-response pairing or more extensive patterns learned over time. In contrast, declarative memory can generally be put into words. Examples of procedural learning are learning to ride a bike, learning to touch type, learning to play a musical instrument or learning to swim. Procedural memory can be very durable.
In cognitive psychology, the term procedural knowledge denotes knowledge of how to accomplish a task, and often pertains to knowledge which unlike declarative knowledge cannot be easily articulated by the individual, or knowledge that is nonconscious. For example, most individuals can easily recognize a specific face as "attractive" or a specific joke as "funny," but they cannot explain how exactly they arrived at that conclusion or they cannot provide a working definition of "attractiveness" or being "funny." Research by a cogntive psychologist Pawel Lewicki has demonstrated that procedural knowledge can be acquired by nonconscious processing of information about covariations.
Studies of people with certain brain injuries (such as damage to the hippocampus) suggest that procedural memory and episodic memory use different parts of the brain, and can work independently. For example, some patients are repeatedly trained in a task and remember previous training, but do not improve in a task (functioning declarative memory, damaged procedural memory). Other patients put through the same training can't recall having been through the experiment, but their performance in the task improves over time (functioning procedural memory, damaged declarative memory).