Non-declarative memory

Implicit memory is one of the two main types of long-term human memory. It is acquired and used unconsciously, and can affect thoughts and behaviours. One of its most common forms is procedural memory, which helps people performing certain tasks without conscious awareness of these previous experiences.

Implicit memory's counterpart is known as explicit memory or declarative memory, which refers to the conscious, intentional recollection of factual information, previous experiences and concepts.

Evidence for implicit memory arises in priming, a process whereby subjects are measured by how they have improved their performance on tasks for which they have been subconsciously prepared. Implicit memory also leads to the illusion-of-truth effect, which suggests that subjects are more likely to rate as true those statements that they have already heard, regardless of their truthfulness.

In daily life, people rely on implicit memory every day in the form of procedural memory, the type of memory that allows people to remember how to tie their shoes or ride a bicycle without consciously thinking about these activities. Research into implicit memory indicates that it operates through a different mental process from explicit memory.

Advanced studies of implicit memory began only a few decades ago. In early research, subjects were presented with words under different conditions and were given two types of tests: recognition memory tests and perceptual identification tests. These studies provided evidence that effects of memory on perceptual identification was independent of recognition memory.Jacoby & Brooks argued that perceptual identity effects reflect very rapid, context-specific learning. Unconscious influences of memory were found to alter the subjective experiences of participants. In one such study, participants judged that the white background noise was lower when they read words they had already been presented, thus misattributing their ease of perceiving the word to less noisy environment. This provided evidence for specific and long-living influences of past memory even when participants were unaware of its influence. Similar effects have been found with studies where participants made judgments about difficulty of anagrams and recognized famous names.

The effect of implicit memory was tested employing priming procedures. Several studies confirm implicit memory as a separate entity. In one such experiment, participants were asked to listen to several songs and decide if they were familiar with the song or not. Half of the participants were presented with familiar American folk songs and the other half were presented with songs made using the tunes of the same songs from group 1 but mixed with new lyrics. Results show that participants in group 1 had a much higher chance of recalling the songs as being familiar, even though in both groups, the tunes of the songs were the same. This study shows that people are even implicitly making connections amongst their memories. Much memory study focuses on associative memory, or memories formed between two entities, linking them together in the brain. This study shows that people implicitly make a strong associative connection between a song's tune and its lyrics that they can't separate later.

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