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Terms and Basic Information

The human memory system involves two primary systems: short-term memory and long-term memory. Miller’s Law, also known as the famous 7 +/- 2 items, is often referenced when referring to the limited operating space in short-term memory, or working memory. This law revealed that a person’s ability to accurately recall information, after a delay in exposure, ranges from seconds to minutes. These 7 +/-2 items are the limit of units of information one is able to maintain; however, capacity is expanded through chunking, or grouping certain information. For example, a phone number is grouped into one unit instead of several separate ones so as to not limit working memory. Long-term memory is more complex and, according to research, consists of three memory systems: semantic memory, episodic memory, and procedural memory. Long-term memory has, potentially, limitless storage capacity and is more stable than short-term memory because it is more specialized when encoding.

Semantic and episodic memory are both part of declarative memory, which means that these types of memories are available to self-conscious awareness and people can report (i.e., declare) that they are present (or not). On the other hand, procedural memory is unconscious. The semantic memory system stores factual knowledge about rules, norms, math or logic, and historical events. This supported various investigations, one of them on the structure and process in semantic memory providing evidence from event-related brain potentials and reaction times.

The episodic memory system is responsible for storing sensorial, perceptual, and affective experiences. It can be in the form of images, such as visual Gestalts or sequences of images from particular points of view. There is a stronger relation to affective valence, which means that the stronger an emotional association is, the higher the probability is for recalling that memory. Studies provide interesting evidence on how dopamine has a great part in encoding episodic memories because of its affectivity.

The third long-term memory system is procedural memory, meaning it's based on unconscious memories. For example, knowledge about the steps and movements made by each part of your body to ride a bike or walk falls into implicit memory. It is categorized as implicit memory because one is not aware of the process of how these actions arise since they have been prepared subconsciously. There is evidence of implicit memory functioning differently than explicit memory in the brain through priming. Procedural memory became more clearly understood through one of psychology's most famous patients, Henry Molaison. Henry Molaison, also known as H.M., had a brain operation that removed various sections of his brain to stop the seizures he was having. As a result, it was thought that he could no longer form new memories. However, through a motor skill exercise that consisted of drawing an image through the reflection of a mirror, it was observed that he was getting better at the skill without remembering why he was good at it. The coordination of his hand movements while observing the mirror appeared natural to him now since it had become an unconscious memory.

Important Aspects of Memory Development

The study of memory development was once centered on strategies and control processes, but now there is more focus on the development of knowledge. There are three major aspects that account for memory development: strategies, metamemory, and content knowledge. All three aspects play major roles in the development of memories and understanding them can lead to substantial improvements in within the field.

Strategies for memory development are cognitive processes that involve organization in order to acquire and retrieve information more effectively. Memory strategies are learned and/or acquired from one’s environment. The number of strategies, as well as the effectiveness of those strategies, changes with age. Some popular strategies include verbal rehearsal, like mnemonics. By implicating strategies, one can increase his/her memory capabilities, leading to improved learning techniques.

Metamemory is the knowledge of one’s own memory and how it works. Developing metamemory is seen in children over seven years of age. This is an important skill for strategically focusing on essential information. This increased awareness and understanding of one’s own knowledge has shown to increase the use of memory strategies and, in turn, improve recall of memories.

Content knowledge influences what an individual is able to remember. The amount of knowledge retained is influenced, to some extent, by what one already knows about a specific subject. Accordingly, this is why it takes more effort for an individual to learn material that they have not been exposed to, as compared to information that has been seen before.

All of these aspects work with one another in order to develop the most efficient level of memory. The more that is known about these aspects and the more they are used, the better that memory can progress in the future. Still, retaining a sharp memory requires effort and will continue to improve with age and practice.

Early Influential Research

In order for memory development in infants to be fully explored, some early research had to first pave the way to make this a possibility. Much of this research stemmed from Jean Piaget’s argument that infants younger than 18 months are incapable of mental representation, and that deferred imitation was not present in infants until about 18–24 months of age. At first, researchers were inclined to disregard early stages of memory development because they assumed that since adults did not recall much of their infantile years, there was not much impact on memory development during those earlier years. In fact, it was not until Evgeny Sokolov published his model of habituation of the orienting reflex during conditioning in 1963, that studies of infantile habituation began to emerge. Using habituation procedures, Werner & Perlmutter were able to obtain the first forgetting function in preverbal infants. This was integral in suggesting how forgetting in infants may reflect the upper limit of short-term memory. Additionally, early studies of classical conditioning were single-subject studies that traced an individual’s conditioning performance over a substantial period of time, providing evidence of long-term memory. Within the late 1950s and through the 1970s, many successful classical conditioning studies were conducted with newborns, but it was not until Blass, Ganchrow, and Steiner demonstrated that 2-hour-old newborns could be classically conditioned that critics finally accepted this notion. Similarly, during this period, researchers were having difficulties operantly conditioning infants because most studies were plagued by the use of discrete reinforcers that were ineffective over long periods. However, with the introduction of the mobile conjugate reinforcement procedure, claims that infants could not learn operant contingencies until they were substantially older were finally put to rest. This mobile procedure has been a cornerstone in the research of infant memory development because it has successfully enabled the assessment of infant capacity for long-term memory.

Current Research

Throughout the last few years, research in regards to memory development has progressed significantly. Researchers found infants difficult to work with and were, and still are, unable to sufficiently comprehend what is going on in an infant’s mind, due to their inexperienced language skills. As stated before, this inhibited research that was based on the developing mind of infants. Although this may have once created an overwhelming barrier upon our knowledge about memory development, advances in methodology have allowed us to realize that much of our memory system is actually beginning to develop during infancy. Such recent experimental methods tend to include conditioning paradigms, recognition memory, and deferred imitation. As a result of these advances, it has been observed that infants learn rapidly, can remember for long intervals of time and, with age, can use what they learn in increasingly novel situations.

In particular, Loucks and Meltzoff built upon the early methods of deferred imitation and applied it to their experiment, which focused on analyzing the impact of goal-oriented situations on children’s memory for action. The results indicated that, like adults, children’s memory for human action is hierarchically organized in relation to goal-situated events. Recent experiments, such as this, help emphasize the unyielding progress of influential research in the field of early memory development.

Another experiment carried out by Barr, Dowden, and Hayne also demonstrates the substantial advances in this field. In this experiment, the infants observed the experimenter perform different actions with a puppet and were tested on their ability to reproduce those actions over an allotted time delay. It was then proven that the ability to recall events from one’s past is already present by the age of 6 months, along with the ability to imitate. Evidently, the cognitive field will continue to thrive and, in turn, answer questions about early memory development which were once so distant to researchers in the past.