How to understand the principles of human memory

The human memory is the storage for all types of knowledge which is made use of by a person working as operating force in a work system. About hundred years ago more serious research has begun on the human memory functionality. It is from thereon that a dualistic view on the memory phenomena has been pursued. It has been found that the memorising performance depends heavily on the recency of the information presented or how often it has been repeatedly experienced. The more refreshment is happening by repetitions of deliberately induced or unintended activations on the same neural traces the more permanent memory is warranted. It seems to be commonsense that there are three categories of memory in the human brain with evident differences in size and retention capacity. These are the sensory, short-term, and long-term memories. We start with that one of the three memory categories, the long-term memory, which contains all permanently available knowledge what is learned by the human operator up to the time being.

This knowledge determines the human operator's behaviour in a given situation in the course of a work process. We can distinguish between two types of long-term memories, the so-called explicit (declarative) ones the contents of which can by virtue become conscious, and the so-called implicit ones which are involved in automatic procedures and which are only becoming globally conscious by way of obvious impingement on something we can observe consciously. We identify our implicit knowledge, if we cannot accurately explain our behaviour in explicit terms. For instance, I can only give a rather global statement that I lift my arm in order to put some food into my mouth. I cannot provide much more detail on the precise kinematics and kinetics of the arm motion or how much force by which muscles is involved in all phases of that action. Implicit knowledge by way of automatic procedures is an important feature, though, for the sake of processing efficiency. The implicit memories are oftentimes also called procedural. This is in particular the case in the context of the motor systems, i.e. for instance the memories for sensori-motor patterns in the cerebellum. Both the explicit and the implicit memories impress with an almost unlimited memory capacity never exhausting during life time and no significant decay rate.

The contents of the explicit memories are about facts (semantic memory) and autobiographical episodic events and experiences (episodic memory). The storage into the episodic memory is achieved almost effortless as opposed to the storage into the semantic memory of facts like concepts, rules or abstract ideas. On the other hand, the reliability of retention in the episodic memory is relatively poor compared to that of the semantic one. It can be stated, though, that both of these memory systems are heavily interacting. A model of the semantically coded representation can be thought of as a high-dimensional semantic space. This might explain that the explicit memories will never be exhausted. As long as explicit knowledge is not verbally represented, individuals often fail, too, to exactly describe anything in verbal terms what is semantically represented. This is usually due to the imperfect linguistic capabilty of accurately expressing semantic contents, to exactly describe anything in explicit verbal terms what is semantically represented in their brain as explicit knowledge. The representation of explicit knowledge might be in various forms when passing through the sequence of memorising stages, depending on the kind of stimuli.

No matter whether the knowledge representation might be visually or acoustically verbalised, provided through images or through feelings like pain, for instance, there is always represented an explicit meaning. Thus, human cognition based on the long-term memories works on a semantic knowledge representation. Therefore, reading a word which can have two different meanings (for example the adjective "light", which can mean the opposite of both dark and heavy), will only lead to ambiguity, if no additional contextual information is available what only very rarely might be the case. There still remains the question about the localisation of explicit knowledge in the cortex. Although the hippocampus in concert with other adjacent neural formations (entorhinal, perirhinal, and parahippocampal cortex (EPPC)) is responsible of the process of storing explicit knowledge, it is not the place where the knowledge is located. It is assumed that it is stored in the associative areas of the neocortex which are pertinent to the modality, quality, and function at question. Thus, the memory of visually experienced objects, for instance, is supposed to be located in the associatve areas of the visual processing system and so on.

The process of recalling an item of the explicit memory is surprisingly efficient. This is an important fact regarding the human role in a work process. Usually, the access to the memory is very fast, in particular in the case of recognition (as opposed to reproduction). The so-called retrieval cues certainly play a significant role in this process. Therefore, the context out of which the memory access is activated is of great influence on the resulting retrieval. Here, it becomes evident that the retrieval process heavily depends on the encoding in the learning process. The contents of the long-term memory are surprisingly stable once they are stored. Continuously, new pieces of knowledge are integrated through the process of learning, but there are almost no losses due to interferences in the course of the learning process. The corresponding neural activation patterns might change, but the semantic code they hold remains the same. In summary, the human long-term memory as a whole is in average operating as a fast-read, slow-write system. While the long-term memory contains the knowledge, which has already been stored in the past, the sensory memory and the short-term memory store new incoming information. The sensory memory is a kind of transient memory for the overwhelming amount of external stimuli with a high decay rate. It exhibits a retention performance of just a few seconds of stimulus-specific activation, then giving room for new incoming information. Within this time span associations between external stimuli or internal projections are taking place, if attention is directed on them. Otherwise the information is lost. The short-term memory has a much longer decay time than the sensory memory, enough to serve as the transient memory needed for the process of learning. This process consolidates the contents of the short-term memory as a part of the long-term memory. All pieces of information which are attended to and adopted by the short-term memory must temporarily have become a part of the working memory. The storage capacity of the short-term memory is very limited with seven (plus/minus two) so-called chunks.

A chunk constitutes a meaningful unit of information which can correspond to any kind of concepts no matter how many bits and bytes it would consume in an artificial memory like that we are used to in a computer. If one would try to desribe a chunk in terms of explicit features and sub-features (attributes), one could possibly succeed in certain cases by use of a fixed number of them, possibly a very small one (or just a single feature). However, this is soly true for only a part of the explicit knowledge which accounts for chunks as objects (like for instance well defined geometrical figures) which are perfectly defined in semantics by symbolic coding. In other cases, though, the number of explicit features and sub-features would shoot up to become countless, if a precise description is intended. These chunks usually consist of implicit features and therefore are implicitly representing explicit knowledge entities. The decay time of the short-term memory depends heavily on the contents and on the occurrence of disturbing events. It can be less than 10 seconds in case of rather unfavourable circumstances, but it can also last for very much longer under certain accommodating circumstances. More recent studies come to conclusions that there is not one unitary short-term memory but rather several ones.

They may be located in different areas of the cortex depending on the contents whether they are modality-specific or associated to the central executive function of voluntary action, for instance. It turns out as a consequence that the capacity limitation is not always quite as strict as it was outlined before. Anyway, the capacity limitation of the short-term memory is one of the greatest drawbacks of human cognition. This is one of the top issues to be accounted for in the work system design. Concerning the memory drawback the introduction of external memories in terms of displays can help a lot (adaptive display presentations). Therefore, the layout of displays for the human operator has been a major realm in work system engineering regarding operation-supporting means.

How to understand the principles of human memory

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