In today's Insight we continue to look at the Atkinson and Shiffrin's multi-store memory model, this time focusing on non-declarative memory, also known as implicit memory.

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Non-declarative memory

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Non-declarative memory (or implicit memory) is the second type of long-term memory besides declarative/explict memory, which was first proposed by Larry Squire in the 80s of the last century. Why the strange adjective "non-declarative"? It stemmed from the difficulty of verbalizing the knowledge to which it pertained to. In contrast to the content stored in the declarative (explicit) memory, where, among other things, abstract information such as knowledge of definitions and classes of objects is stored, here we are dealing with type of knowledge, the articulation of which is difficult - primarily because its encoding in the memory did not occur by means of language. So we already have some clue what kind of "content" the non-declarative memory stores - these content are difficult (but not impossible!) to describe in words.

But why is it "implicit"? Well, because we do not have fully conscious access to it. The contents of this memory "recall itself" in a proper context and we do not need to make any conscious effort to recall it. Something completely opposite happens with declarative memory (while using it we sometimes almost fight internally to recall some information, e.g. during an exam!). The information extraction processes are therefore of an automatic nature in implicit memory.

While during the use of declarative memory, in addition to the hippocampus, the cortex of the frontal and temporal lobes are also activated, in case of non-declarative memory, in addition to the hippocampus, the motor cortex and cerebellum are active.



Let's move on to see what types of implicit memory we use, as they differ from each other quite considerably!

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Procedural Memory

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Procedural memory refers to various skills that a person has mastered during his or her life. Information (or perhaps "experience" is a better term) is incorporated into this memory through direct sensory experience and interaction with the environment. Learning process is much slower than in case of declarative memory, but what is learned lasts almost a lifetime and will hardly be forgotten - you can't forget how to ride a bike (at least not without a brain injury!)

Speaking of which, do you remember the moment you learned how to ride a bike? How difficult was it to maintain the accurate balance, what was the effort to keep the bike upright during the more difficult corners? After several hours of riding and several falls, one can manage to remember unconsciously the way of moving one's legs, body and balance, so as to keep straight ride without any problems. After a few months, the procedural memory adds more and more difficult cycling manoeuvres to its "base" and you can already race through difficult terrain or even jump out of the ramps! Those who practice cycling professionally, be it cyclists or downhill riders, go even further - their muscles (or rather the procedural memory) acquire so much precise information that it allows them to almost fully control their body and the bike and make the art of cycling near perfect.

With procedural memory, we no longer need to consciously focus on the motoric aspect of our operations, so we have the time and resources to take strategic decisions. In the case of cycling, these would be the decisions about where to go, what technique to use, how to plan the next jump from the ramp, etc.

Other examples of skills that use memory are writing, reading, walking, driving, flying a plane and even speaking (!). All these skills had to be consolidated by a tedious repetition of sensomotor activities.

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Conditioning

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Conditioning, discovered by Ivan Pavlov, is also based on the functioning of non-declarative memory.
Conditioning is based on the development of appropriate habits, which are nothing other than the relationship between stimuli and reactions. The learned reactions are stored in non-declarative memory so that they are revealed without the participation of consciousness. Many (if not most) of the reactions we have learned we are not even being aware of! Traditionally, there are two types of conditioning:

• classical conditioning - Pavlov noticed that when dogs are given a bowl of food, they immediately start to emit more saliva (because the autonomous nervous system is stimulated while being exposed to food stimuli). He also discovered that if this phenomenon is accompanied for some time by another stimulus, e.g. the sound of a bell, after some time it is enough to use the sound of a bell alone to cause salivation in dogs! This is the phenomenon of classical conditioning, and it's another example of a type of "knowledge", or rather an experience, which is a part of implicit memory.

_{Illustration of classical conditioning
image source}

• instrumental (or operant) conditioning - is about learning to respond accordingly by using rewards (reinforcements) or by punishments (or by stopping giving rewards). This is exactly how animals are trained or... how children are raised (or at least this is one of many methods people use to raise their children). The rewards encourage the subject to use the response that the rewards give rise to. In people certain behaviours are later already so internalized, that they do not require rewards, e.g. we no longer require sweets to make a stool into the toilet, not to the nappy :P Reactions learned through instrumental conditioning are also a kind of experiences contained in the non-declarative memory.

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Priming

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Priming is another phenomenon based on implicit memory.
Let's look at the picture below!

_{image source}

Which letter would you use to fill the gap?
OK, and which letter would you choose in the picture below?

_{image source}

You've probably already understood what priming is all about! If you mind told you to put "soup" in the first case and "soap" in the second case, you are very likely to have been subjected to priming!

Priming occurs through exposure to certain stimuli, which then affect the perception or simply the processing of other, following stimuli. Earlier stimuli, in this case food and bath products, trigger association networks, or simply a grid of different associations related to the context of the stimulus. This affects the way we solve the tasks, because the associations (i.e. in fact the memories from the experience with these subjects!) impose a specific solution in their context! Note that I did not impose in any other way on what letter should be added to the word. Implicit memory acts automatically, without our will!

While it seems obvious and clear in this context, priming is not always so trivial. This phenomenon usually works without any participation of consciousness and without any realization that it's affecting us. Even stimuli that the consciousness cannot register can affect our cognitive functioning, although the message must be as simple and rather non-verbal as possible (e.g. a scheme of a smiling face). This is know as subliminal stimuli. However, walking around the city surrounded by hundreds of non subliminal advertisements, we are also subjected to priming and non-declarative memory immediately evokes these (usually unaware) associations while we do our shopping..

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Non-associative Memory

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The last type of non-declarative memory described here will be the non-associative one. What is hidden under this mysterious name? This memory refers to individual stimuli that are not linked to other stimuli (such as rewards, punishments or other types of contextual stimuli). We distinguish two types of non-associative memory, which are their opposites:

habituation - occurs when a stimulus is repeated and does not bring about any significant change or information. This can be a repetitive noise, which at the beginning can alarm and disturb us, but after some time we completely stop paying attention to it and we can even fall asleep with it. This is because non-declarative memory records that this noise carries no information and is predictable. This allows us to devote our valuable cognitive resources to other tasks.

_{Habituation makes a scarecrow just a short-term solution
image source}

• sensitization - is the opposite of habituation. Sensitization takes place when the stimulus that occurs differs from the stimulus sequence that the individual has previously recorded. This results in increased attention being paid to the observation of this stimulus. Non-declarative memory in this case compares the information previously collected with new information that does not match the pattern. For example, when the sound that a fridge produces rapidly changes, we start to take notice of it, in spite that previously we completely did not register it consciously.

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As you can see, the four types of non-declarative memory listed above do not have many common features. This category was formed to put into one bag all types of memory that were distinguished apart the declarative memory. All of them, however, are characterized by automatic, unconscious functioning and the difficulty of verbal transfer "what actually is remembered". As I tried to show in my last two Insights entries - the performance of human memory is not homogeneous, it is not a single system that we can find in one place in the brain. And I must add that I have barely grasp the subject, as there is still an ultra-short memory, a prospective memory and a few more... I may come back to this topic in future entries!

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Literature

_{Maruszewski, T. (2001). Psychologia poznania. Gdańskie Wydawnictwo Psychologiczne.
Nęcka, E., Orzechowski, J., & Szymura, B. (2006). Psychologia poznawcza. Academica Wydawnictwo SWPS.
Rescorla, R. A., & Wagner, A. R. (1972). A theory of Pavlovian conditioning: Variations in the effectiveness of reinforcement and nonreinforcement. Classical conditioning II: Current research and theory, 2, 64-99.
Schacter, D. L. (1987). Implicit memory: History and current status. Journal of experimental psychology: learning, memory, and cognition, 13(3), 501.
Tulving, E., & Schacter, D. L. (1990). Priming and human memory systems. Science, 247(4940), 301-306.}

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Previous entries in the Insight series:

Insight #1: Brand new psychology series on Steemit! What is insight?

Insight #2: What emotions are and what are they really for?

Insight #3: Personality Trait Theory - psychological theory that lead Donald Trump and Brexit to WIN

Insight #4: Attributions - how and why we judge ourselves differently from others

Insight #5: Verbal thinking - a "hardfork" of speech

Insight #6: Do we see more than we suppose? Two separate vision systems hypothesis

Insight #7: Effectiveness and Arousal in Introverts and Extroverts

Insight #8: Declarative Memory - how is our knowledge stored?

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