Implicit 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 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 in the 1980s. 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. Some clues as to the anatomical basis of implicit memory have emanated from recent studies comparing different forms of dementia. Patients with dementia of the Alzheimer type (DAT) have been reported to be severely impaired on both lexical and semantic priming tasks, while patients with Huntington's disease (HD) were able to demonstrate normal priming ability (Shimamura et al., 1987; Salmon et al., 1988). In contrast, HD patients evidenced little learning on a pursuit-rotor task that was easily mastered by both amnesic and DAT patients (Eslinger and Damasio, 1986; Heindel et al., 1988). This possible double dissociation involving HD and DAT patients suggests that different implicit memory tasks are mediated by distinct neural systems and that these tasks can be used to differentiate some of the so-called 'cortical' (e.g., DAT) from 'subcortical' (e.g., HD) dementias (Cummings and Benson, 1984). A more recent contribution to the study of implicit memory comes from the experiments with a spatial organization computer game on amnesic patients (Stickgold et al., 2000). Damage to the bilateral temporal lobe and hippocampus had caused the loss of explicit memory. However, despite being unable to recall the game, these patients were able to dream of it at sleep onset. This observation is interesting as it shows that learning can be memorized without the contribution of explicit memory, which requires the activation of the hippocampus and of the temporal and basal cortex. In the cases observed by Stickgold et al., the explicit memory was definitely impaired, but a non-explicit and non-conscious kind of memory was left and could emerge in dreams. This observation shows that an experience can be stored in the implicit memory and can be represented symbolically in dreams. According to Daniel L. Schacter, 'The question of whether implicit and explicit memory depend on a single underlying system or on multiple underlying systems is not yet resolved.' The findings display such a variety of phenomena that there has not yet been a theory to account for all of the observations. Instead, two theories have been presented to explain different subsets of the data.