Implicit memory is one of the two main types of long-term human memory in psychology. It is acquired and used unconsciously, and can affect thoughts and behaviors. Implicit memory is sometimes referred to as unconscious memory or automatic memory. It uses past experiences to remember things without thinking about them. Implicit memory is enabled by previous experiences, no matter how long ago those experiences occurred. A subset of implicit memory, procedural memory, enables us to perform many everyday physical activities, such as walking and riding a bike, without having to give it thought. Priming is another, smaller subset of implicit memory. It involves using pictures, words, or other stimuli to help someone recognize another word or phrase in the future. Examples of implicit memories include recalling the words to a song when someone sings the first few words, riding a bike, performing simple cooking tasks, such as boiling water for pasta, and driving a car. Implicit memory differs from explicit memory, also called declarative memory, which involves a conscious attempt to retrieve memories of past events. While implicit memory requires little if any effort to recall, explicit memory requires a more concerted effort to bring memories to the surface.