Introduction
Human memory has long been a subject of research and scientific debates, and biology, psychology, and neuroscience are still reaching new frontiers in studying this phenomenon. The development of computer technology in the 1950s and 1960s has advanced scientific understanding and drew a parallel between computer and brain processes. Today, the most common definition of memory is the faculty of the human brain allowing information encoding, storage, and retrieval. However, the assumption that akin to a computer the human brain merely “copies” the original experience is simplistic at best and misleading at worst. While research on human memory has been proliferating in the past few decades, it has also led to plenty of inconsistencies in the field. The purpose of this paper is to review the current research on encoding, storage, and retrieval processes as well as short-term and long-term memory, providing practical implications for psychologists and specialists in related fields.
Encoding
Encoding is one of the key memory processes that means the transformation of incoming information (sensory input) into a form that is palatable by the human brain and apt for further storage. There are a few ways in which incoming information can undergo encoding: visual (pictures), acoustic (sound), and semantic (meaning) (Radvansky, 2015). The existing scientific consensus suggests that acoustic and visual are the primary encoding principle in short-term memory (STM). Simply put, when presented with new information, such as a list of numbers, a person is likely to memorize them by verbally rehearsing or retaining the visual representation of the object (Radvansky, 2015). Conversely, long-term memory (LTM) relies primarily on semantic coding (by meaning), though the principles of encoding may vary from person to person.
Current research works toward identifying the factors that affect and improve memory encoding. New findings promise not only to empower the learning process by integrating human brain cues but also mitigate memory loss that is an unavoidable part of aging. Makowski et al. (2017) are convinced that presence, or in their words, “being there,” boosts memory encoding. Their research hinges on the well-grounded assumption that the quality of the encoded memory trace is shaped by various characteristics of stimuli as well as by the physical and mental state of a person during the encoding. Machowski et al. (2017) enlist the “pillars” of presence identified by recent literature: first-person perspective, interactivity, attention, and emotional engagement.
However, the scholars argue that presence does not have to be real: it may as well be a simulation that will arguably lead to the same improved memory outcomes. Makowski et al. (2017) hired 268 participants that were offered to watch the same live-action movie (Avengers) either in 2D or 3D format. After watching the movie, participants filled a questionnaire that measures dimensions such as emotional experience, presence, factual memory, and temporal order memory. The findings showed that subjective presence was associated with the intensity of emotional reactions and, in turn, improved factual memory. However, temporal order memory remained unaffected by enhanced presence due to 3D technologies.
In her research, Cheke (2016) draws on similar theoretical underpinnings as she argues that remembering the context of “where” and “when” something happened helps with creating associations that, in turn, boost memory encoding. She then proceeds with hypothesizing that age-related memory deficits may be ascribed to faulty associative ties that include distractor items or irrelevant environmental features. For her study, Cheke (2016) recruited younger and older participants; both of the groups played the treasure hunt game while employing the “what –where – when” episodic memory strategy. The findings suggested that older participants benefited the most from the strategy as it lightened the burden on working memory and attentional resources. The two studies provide cues for medical doctors, psychologists, social workers, and other specialists working with elderly clients and adults with otherwise impaired memory encoding.
Storage
There is not a single part of the brain that stores all the memory; instead, the storage location is defined by the type and use of memories. Explicit memories (information about events where a person was present, general facts, and information) are stored in the hippocampus, the neocortex, and the amygdala. For implicit memories, also referred to as unconscious or automatic memories, the most crucial brain regions are the basal ganglia and cerebellum (Radvansky, 2015). Short-term working memory relies most heavily on the prefrontal cortex (Radvansky, 2015). They allow a person to perform tasks without thinking about them on purpose: for instance, a person can easily brush teeth without any conscious effort because their actions will be guided by implicit motor memory. Lastly, the storage of short-term working memory needed for the completion of a task at hand takes place in the prefrontal cortex.
It has been established that there is no specific site where all memories are stored. Yet, the question arises as to whether their location depends on their type. Fougnie et al. (2015) provide evidence that the storage of working memory in humans may be domain-specific. In their study, Fougnie et al. (2015) assessed participants’ performance when completing concurrent visuospatial and auditory tasks. The findings show that the performance of the two tasks is independent of each other. The paper concludes that while some regions are domain-independent, which is at the moment, the dominant idea in neuroscience, others are responsible for storing specific types of information.
Christophel et al. (2018) refer to human memory storage as a distributed system with engaged regions ranging from sensory to parietal and prefrontal cortex. One explanation that Christophel et al. (2018) provide is the nature of memory encoding before storage: the scholars point out the gradient of abstraction from the processing of low-level sensory features to more complex abstract, semantic encoding. This phenomenon also leads one to the realization that all the brain regions responsible for storing memories do not work independently from each other. Conversely, their contributions are best defined in terms of representational stages with varying levels of transformation and abstraction (Christophel et al., 2018). The paper concludes that the scientific community might need a paradigm shift when it comes to understanding memory storage. The focus should be not on the storing functions and capacities of each region but rather on their interaction and collaboration.
Retrieval
The concept of memory retrieval refers to accessing memories from the past. There are several types of retrieval: recall, recollection, recognition, and relearning (Radvansky, 2015). A recall is the type of retrieval that occurs without any external cue (e.g. filling one’s name when registering on the website). Unlike recall, recollection requires a conscious effort in the form of logical structures, partial memories, narratives, or clues. In other words, recollection “reconstructs” a memory, using internal and external evidence. Recognition refers to the realization that something is indeed familiar when encountering it (e.g. a song sounds familiar, but the listener cannot quite put a finger on where they heard it before or the name and the artist). Lastly, relearning help when information has now been rendered inaccessible; experiencing it again strengthens memories and makes them retrievable with greater ease in the future.
Retrieval is critical for guiding a person’s current thoughts and decisions and being able to handle day-to-day tasks. For this reason, psychology, neuroscience, and related fields are concerned with identifying factors that affect memory retrieval. One of such factors is the stress that triggers specific endocrine responses influencing multiple human memory processes at once – encoding, storage, and, obviously, retrieval. Wolf (2017) explains that it is common for humans to remember an extremely frightening or unnerving experience (assault, terrorist attack, failed job interview, and others) for a lifetime. However, such memories become easily accessible and as vivid as they were on the day of the occasion, other important memories may become suppressed while a person is under stress (Wolf, 2017). What is more, the impairing effects of stress on memory retrieval may last and interfere with an individual’s daily functioning longer than it was initially understood.
To further prove these assumptions, Stock and Merz (2018) carried out a controlled trial for which they recruited forty healthy male students. The difference between the control and intervention groups was exposure to psychological stress. For a better assessment of memory retrieval mechanisms under stress, students had to study a material that contained diverse types of information: coherent text, visual information, numerical, and others. The follow-up assessment was conducted 24 hours after the exposure. Stock and Merz (2018) chose the socially-evaluated cold pressor test for the intervention group: each participant had to submerge their dominant arm and forearm into ice-cold water while having a stranger look at and videotape them. Control group participants showed better retrieval of visual and numeric items, while those exposed to the stress test surpassed them in retrieving verbal information. Another curious finding suggested that higher levels of cortisol improved memory retrieval, which provides further support for exposure in psychotherapy of phobias.
Short-Term and Long-Term Memory
Short-term and long-term are two main types of memory, and as the name suggests, the key difference between them is duration. The concepts have generated quite a lot of controversy in the fields of cognitive psychology and neuroscience. Norris (2017) explains that for over a century, scientists have believed that the human brain operates two different systems for storing short-term and long-term memories. However, according to the researcher, such claims relied on either sparse experimental or purely introspective data. The holders of dissenting views, to which Norris (2017) himself belongs, argue that there is a single memory system responsible for handling both short-term and long-term memories.
Within this paradigm, short-term memories have the capacity of converting to long-term memories. In turn, when activated, the latter become the former and can be used to guide current thoughts and decisions. Norris (2017) supports his argument with neuroimaging data that suggests the presence of a single system with a complex binding mechanism and pointers facilitating interactions between LTM and STM. However, what remains unclear is the activation of LTM to become STM. It may be possible with the help of an additional activating mechanism.
In their research, Missaire et al. (2017) concern themselves with the former mechanism: they seek to pinpoint how exactly STM becomes LTM. The scholars assume that STM, which they equate with WM (working memory), is erased and reset shortly after being utilized. The human brain does so to prevent itself from overflooding with irrelevant information that would interfere with newly stored input. Missaire et al. (2017) experimented with rodents that were completing radial maze tasks. The tasks are typical for assessing WM as they require animals to memorize paths for quick decision-making. The findings suggest that the content of WM may not be immediately erased or forgotten, which contradicts the resetting theory. In some cases, the memories were stored for days, which makes one wonder whether it is possible for all types of WM or only geospatial information.
Conclusion
Human cognition is critically dependent on the ability to memorize information and use it in a variety of contexts. Today the research on human memory and all its functions, such as encoding, storage, and retrieval, may provide useful practical implications as well as resolve old or generate new controversies. The quality of encoding varies a lot depending on the attentional engagement, subjective presence, and emotional intensity. The gradient of abstraction when encoding sensory input into more abstract representations engages multiple brain regions that are also responsible for memory storage, creating a distributed system. Memory retrieval is affected by emotions and, especially, stress responses that may eventually lead to impairments. Humans utilize both short and long-term memory whose duration as well as belongingness to the same or distinct systems are still debated.
References
Cheke, L. G. (2016). What–where–when memory and encoding strategies in healthy aging. Learning & Memory, 23(3), 121-126.
Christophel, T. B., Klink, P. C., Spitzer, B., Roelfsema, P. R., & Haynes, J. D. (2017). The distributed nature of working memory. Trends in cognitive sciences, 21(2), 111-124.
Fougnie, D., Zughni, S., Godwin, D., & Marois, R. (2015). Working memory storage is intrinsically domain specific. Journal of Experimental Psychology: General, 144(1), 30.
Makowski, D., Sperduti, M., Nicolas, S., & Piolino, P. (2017). “Being there” and remembering it: Presence improves memory encoding. Consciousness and Cognition, 53, 194-202.
Missaire, M., Fraize, N., Joseph, M. A., Hamieh, A. M., Parmentier, R., Marighetto, A.,… & Malleret, G. (2017). Long-term effects of interference on short-term memory performance in the rat. Plos One, 12(3), e0173834.
Norris, D. (2017). Short-term memory and long-term memory are still different. Psychological Bulletin, 143(9), 992-1009.
Radvansky, G. A. (2015). Human memory. Psychology Press.
Stock, L. M., & Merz, C. J. (2018). Memory retrieval of everyday information under stress. Neurobiology of Learning and Memory, 152, 32-38.
Wolf, O. T. (2017). Stress and memory retrieval: Mechanisms and consequences. Current Opinion in Behavioral Sciences, 14, 40-46.