When going through the process to obtain a driver’s license, you had to take a written exam. You may have been asked the following question:

When approaching a school bus with its stop sign extended and red lights flashing, you must:

1. Slow down to pass cautiously
2. Stop if children are crossing
3. Stop regardless of children crossing and your direction of travel
4. Continue driving if you’re in the opposite lane

You reflect on the notes you studied and the practice exams you took in the days leading up to the exam to remember that the correct answer is C. In this scenario, you tried to intentionally recall a learned fact, drawing on your explicit memory to answer the question.

Explicit memory, sometimes referred to as declarative memory, is information that requires purposeful and conscious effort to recall. Often, knowledge is deliberately encoded into long-term memory by rehearsal, through acts like studying. Other times, life events, particularly those that are highly emotional and important to you, will also become part of your explicit memory. If asked what you felt like on your wedding day, you’d be able to recall it as if it happened yesterday. You’re likely to be able to specifically pinpoint how and when you have come to know knowledge stored in explicit memory, as opposed to your brain unconsciously committing it to memory, which is the case for implicit memory. Implicit memory is information stored in our brains unconsciously, that we don’t purposefully try to remember, like knowing how to brush your teeth.¹

Explicit memory and implicit memory are different types of long-term memory that often work together to help you navigate day-to-day life. For example, if you’re riding your bike to your friend’s new house, you remember how to pedal and keep balance thanks to implicit memory, while you know the route by explicitly memorizing it beforehand.¹ 

Encoding: The processing of new sensory information into a usable format for longer-term storage and retrieval. We encode new information by perceiving it and relating it to past knowledge and experiences.⁴ For example, if while studying for a history exam, you learn that World War II ended in 1945, you may relate that to being 27 years after World War I ended, a connection that helps you explicitly remember both pieces of information.

Retrieval: The process of taking information out of our memory storage when we recall it at a future date. For explicit memory, retrieval is typically conscious, where you purposefully try to remember information or a personal experience. 

Long-Term Memory: The transfer of information from short-term to long-term storage in your brain to commit lasting memories. Our long-term storage is relatively unlimited and stable, allowing us to remember information for many years, although we are prone to making mistakes when recalling the information. Anything remembered just a few minutes up to decades ago is considered to be retrieved from our long-term memory, as information is only stored in short-term memory for 15-30 seconds.⁵

Semantic Memory: A subtype of explicit memory that involves general knowledge about the world, such as knowing that the capital of Canada is Ottawa or who the current President is.⁵ 

Episodic Memory: A subtype of explicit memory that involves information about specific personal events, such as remembering the speech you gave at your high school graduation, or the emotions you felt when your child was born.⁵

Implicit Memory: Information that is stored in our long-term memory unconsciously and without intention. It is usually also retrieved in an automatic, unintentional way. For example, typing without looking at the keyboard relies on implicit memory.

In 1968, psychologists Richard Atkinson and Richard Shiffrin developed a multi-store model of memory. Previously, it was assumed that memory was a single, undifferentiated process, but Atkinson and Shiffrin suggested there were actually three different memory stores, and that information is transferred between them in a linear fashion. Our sensory memory store takes in information from the environment, and if attention is paid to it, it then moves to short-term memory. Next, some of that information is consolidated into our long-term memory.⁶ 

Initially, it was believed that all memories in our long-term storage were encoded and recalled in the same way. However, in 1953, the case of Henry Gustav Molaison, known in scientific literature as H. M., led to the discovery of the distinction between implicit and explicit memory. Molaison had severe, treatment-resistant epilepsy, leading a neurosurgeon to remove most of the medial temporal lobes of his brain in an attempt to control his seizures, destroying structures like the hippocampus in the process. After the surgery, Molaison suffered from anterograde amnesia, seemingly unable to form new long-term memories. 

What was peculiar about Molaison’s case was that not all of his long-term memory was impacted. He was able to learn new motor skills, quickly improving his hand-eye coordination over several iterations of a task, though he couldn’t recall having tried the task before. While psychologists did not initially have a framework to interpret his symptoms as evidence of distinct memory systems, they were becoming aware that different types of information are encoded and stored differently in the brain. In combination with other cases where brain injury and trauma impacted memory, and the development of the multi-store model of memory, Molaison’s case led to the differentiation of two types of long-term memory: implicit and explicit.⁷

In the 1970s, Endel Tulving and Daniel Schacter further developed the concept of explicit memory by dividing it into two different types: semantic and episodic. Semantic memory deals with general knowledge and facts, whereas episodic memory deals with personal experience.⁸ Tulving and Schacter had conducted neuropsychological research on patients with brain injuries and found that some were able to remember semantic information but not episodic, and vice versa. One patient, K.C., suffered severe amnesia after a motorcycle accident and was unable to remember many personal experiences that took place before the accident. However, K.C. was able to recall general knowledge of the world, suggesting a dissociation between episodic and semantic memory.⁹ 

Later, thanks to advances in neuroimaging, brain scans were able to confirm Tulving and Schacter’s theory, revealing that both episodic and semantic memory depend on the hippocampus for encoding. For episodic memories, the hippocampus is also always involved in retrieval; however, some semantic memories, when well learned, no longer depend on the hippocampus for retrieval—they become mere facts that we know without necessarily remembering how or when we learned them.¹⁰ 

Today, the study of explicit memory continues to evolve through interdisciplinary research that blends cognitive psychology, neuroscience, and computational modeling. Understanding how memory works is important to inform strategies for knowledge retention in education, and can support strategies for patients suffering from brain damage or therapies for trauma and depression, where recalling explicit memories may be an important aspect of recovery.

Richard Atkinson & Richard Shiffrin

American psychologists and cognitive scientists whose most fundamental contribution to the field was the development of the multi-store model of memory, suggesting that information passes through various stores in a linear fashion. Atkinson is also known for pioneering the use of mathematical modeling for illustrating complex psychological phenomena,¹¹ while Shiffrin spent the majority of his career discovering how attention works and is related to memory.¹²

Henry Gustav Molaison

A patient whose case led to a breakthrough in the distinction between explicit and implicit memory in our long-term storage. Molaison had been hit by a bicycle at the age of 7, which caused him to start having epileptic seizures that worsened as he got older. His seizures prevented him from holding a steady job or leading a normal life, pushing him to get brain surgery, during which parts of his amygdala and most of his hippocampus were removed.¹³ Afterwards, he was unable to encode new memories like facts and faces, although he could quickly acquire new motor skills and could still remember many personal experiences from before the surgery. This led researchers to differentiate between explicit and implicit memory.¹⁴

Endel Tulving

A Canadian psychologist whose research into memory caused a paradigm shift from the established belief that all types of memories were stored and processed in the same way in our long-term storage. Tulving proposed that there were two different types of explicit memory—episodic and semantic—that relied on different patterns of brain activity. Later in his career, Tulving also made a distinction between encoding and retrieval, showing that there are differences in how information is stored and how it is accessed.¹⁵ 

Daniel Schacter

An American psychologist who, when he was Tulving’s graduate student, changed the way that people understood and researched memory. The pair suggested that explicit memory could be divided into two kinds: episodic, surrounding information related to personal experiences and events, and semantic, surrounding general information about the world.⁸ Schacter also provided valuable insight into the ways that our brain reconstructs memories when recalling information, which can cause the memories to be distorted. He further made an important association between constructive memory and imagination, suggesting that the former allows us to do the latter.¹⁶

Kent Cochrane

A memory disorder patient, known as patient K.C., who has been significantly researched to support Tulving and Schacter’s theory that explicit memory is composed of both episodic and semantic memory. When he was 30 years old, he fell off his motorcycle after skidding off an exit ramp, which put him in intensive care for several weeks. His brain damage was severe, including the loss of his hippocampus on both sides, which prevented him from remembering his past or making new memories. After further investigation, Tulving found that Cochrane could only remember semantic information related to facts and general knowledge, but nothing about his personal experiences. His case provided evidence that our episodic and semantic memories rely on distinct processes in the brain.¹⁷

Our understanding of explicit memory—how we consciously store and retrieve facts and experiences—has far-reaching consequences beyond the lab. From improving how we learn to shaping how we treat trauma and design artificial intelligence, research into explicit memory continues to influence and enhance real-world systems.

Improving Learning Strategies

Any research that contributes to a better understanding of the way that we retain information is going to have a positive impact on education. By understanding how our brain processes, stores, and retrieves information, educators can develop the best strategies to support students’ learning.

One learning strategy that was developed thanks to our understanding of explicit memory and the distinction between semantic and episodic memory is spaced repetition. Often, exams and standardized tests require students to remember facts, which we recall from our semantic memory. Research showed that explicit memory, particularly semantic, benefits from spaced repetition, where the information is presented across various temporal intervals. Spaced repetition prompts students to encode and retrieve information multiple times, strengthening the synaptic connections to make recall easier.¹⁸ Repetition causes the information to no longer be tied to a specific time or event, which reduces the burden on the hippocampus during an exam.¹⁹

Revolutionizing Therapy Treatments

Through a better understanding of the differences in how explicit and implicit memories manifest in individuals experiencing mental health challenges, therapies can be adapted to best support clients. 

In eye movement desensitization and reprocessing (EMDR) therapy, therapists work with clients to recall emotionally distressing memories while moving their eyes to process the trauma in their brains more healthily and change established neural patterns. Knowing whether a client is dealing with painful explicit or implicit memories changes the approach. With episodic memories, clients will often know exactly when the memory was made and can clearly describe the emotions and beliefs related to the event. Therapists are therefore able to work in a linear fashion to help them process those distressing emotions, whereas with implicit memory, often the source of the memory has to first be discovered.²⁰ 

Shaping the Design of Artificial Intelligence

AI tools like ChatGPT are built with the intention of mimicking human intelligence, and through extensive training on large amounts of text data, they are able to retrieve information when prompted, similar to our own recollection of explicit memories.

AI tools require the ability to store vast amounts of semantic data in a similar way to how we store semantic memory, where factual information is encoded through the analysis of data, and can be recalled when prompted. AI’s semantic memory is what allows it to provide you with the answer to questions like “When was the Declaration of Independence signed?”. For this type of question, it doesn’t need to know when or from where that information was encoded, allowing it to quickly locate the information in its store and provide you with an answer.

In other instances, AI tools must be able to contextualize the knowledge within past interactions or experiences. For example, in customer service, AI chatbots perform better when they are able to recall previous conversations they’ve had with the customer to offer personalized support. If you ask a chatbot about the status of your delivery, it should remember your order number from previous interactions to give you a faster, more relevant response.²¹ 

Although explicit memory has been widely studied and categorized, researchers continue to debate exactly how it functions and interacts with other types of memory. These controversies raise important questions about how memory is stored, accessed, and even defined.

Does Explicit Memory Function as a Distinct Memory System?

While it is generally agreed upon that the terms explicit and implicit describe different types of memories, there is some controversy as to whether they rely on different brain systems. However, the research into explicit versus implicit memories is often testing different things: explicit memory tasks require recalling facts and experiences (knowing that), whereas implicit memory tasks require the application of skill that is often unconscious (knowing how). The distinction might therefore just reflect how we measure different types of memory, not how the brain actually stores it. 

Priming, a phenomenon where exposure to a stimulus influences our response to a related stimulus later on, presents an interesting exploration of whether explicit and implicit memory use different systems. Research has used priming as evidence of implicit memory, with the belief that someone doesn’t consciously intend their behavior to be impacted by recalling the earlier stimulus. For example, if you see an advertisement for soda with the tagline “Thirst-quenching,” and later visit a grocery store and are choosing which soda to buy while you’re thirsty, you don’t necessarily try to remember the advertisement. Your brain unintentionally remembers and guides you to buy a particular soda. 

However, some research has shown that priming still occurs for explicit memory tasks. Jacoby and Whitehouse conducted a study in which participants studied a list of words. They were then asked to recall whether the word being shown on the screen was old (was in the previously studied list) or new. Before seeing the word which they had to categorize, they saw a briefly flashed word (too quickly to be consciously perceived). The results showed that if the briefly flashed word matched the next word they had to categorize, participants often falsely said the word was old. This study showed that priming, an unconscious process, impacted explicit memory, a conscious process, which blurs the line between which systems are at play during explicit and implicit memory tests.²²

Interdependence of Episodic and Semantic Memory

While Tulving made a distinction between two different types of explicit memory, semantic (general knowledge) and episodic (personal experiences), some researchers suggest that the two forms are interdependent. 

While patients with amnesia can sometimes remember semantic information but not episodic, or vice versa, other studies show that having one of these forms of explicit memory intact can support the formation of the other. In one study, amnesic patients were asked to study the prices of grocery items. Some of them corresponded with actual prices that would be found in grocery stores, e.g., $4.10 for a gallon (3.8 liters) of milk, while others did not, e.g., $17.99 for a dozen eggs. Patients who had intact semantic memory were able to better memorize the prices for the items that were congruent with their prior experience, in other words, their semantic knowledge, and form new episodic memories. The same was not true for patients with damaged semantic memory, which suggested that semantic knowledge helps us to register new experiences by acting like a scaffold from which to build upon. ²³

Memorization May Be Counterintuitive

It usually takes a purposeful effort to turn knowledge into explicit memory, which is why you might repeat important reminders (like “Pick up the laundry”) to yourself or study for an upcoming exam. However, memorization may not actually be the best way to learn, or even to remember. As American neuroscientist Lisa Genova writes in her book, Remember,  “Ironically, if you jot down what happened today, you’ll probably limit what you remember about today to the details you’ve chosen to record.”²⁴

Rote memorization often leads to weaker long-term memory retention, which is why study methods like cramming are not advised. Even if you do manage to store information like facts in your explicit memory, you aren’t necessarily going to have a deep understanding of the concept or how it relates to other ideas.²⁵ That’s why for semantic memories in particular, you tend just to remember the fact, not where or how you learned it. 

Lonni Sue Johnson: The Artist with Amnesia

In 2007, artist and illustrator (and amateur pilot!) Lonni Sue Johnson, whose work had been featured in children’s books and the prominent magazine The New Yorker, contracted a case of encephalitis. Encephalitis is an infection that causes the inflammation of brain tissue, which can lead to severe brain damage. That was the case for Johnson, who at the age of 61, was suddenly unable to remember most of her life due to damage in her hippocampus.²⁶
In the immediate aftermath of the disease, Johnson could not walk, write her name, or even hold a pencil. She had lost most of her memories and struggled to form new ones; however, it seems her creative and artistic capabilities remained. Over time, she regained some of her motor skills and was able to create beautiful pieces of art, play music, and explain concepts related to flying a plane. These are all related to procedural skills that are retained as implicit memories. While she remembered very few life events and struggled to retain any new experiences, she could complete word puzzles, draw, and compose.²⁶

Johnson’s case provides evidence of the distinction between explicit and implicit memories, and also highlights the power of passion: Johnson showed the most progress in recapturing the skills for the things she loved most.²⁷

Highly Superior Autobiographical Memory

Highly superior autobiographical memory (HSAM) demonstrates the incredible potential of episodic memory. Only around 100 people worldwide have HSAM, and for that small group of people, their episodic memory seems limitless and permanent. 

One 18-year-old Canadian girl, Emily Nash, recently learned that her ability to recall every single day of her life in impeccable detail was a case of HSAM. If you were asked what happened on March 4th, 2019, you’re likely to stutter and struggle to remember even a single detail. Nash, on the other hand, would be able to immediately tell you that it was the day Luke Perry died, information she learned on the radio when her mom picked her up at school to take her for lunch. While Nash is great at remembering personal experiences, she isn’t generally better at remembering procedural tasks or skills, suggesting that HSAM is related to explicit memory. 

Cases like Nash’s have caused researchers to try to find what causes some people—a rare few—to have this incredible explicit memory, in hopes that it may help restore memories for individuals with early Alzheimer’s disease. By pinpointing which areas of the brain show greater activity in individuals with HSAM, scientists can use transcranial magnetic stimulation to provoke activity in these same areas. 

Carmen Westerberg, a psychologist and sleep researcher, monitored Nash’s brain activity as she slept, as sleep is thought to be integral to memory consolidation. Westerberg has studied other individuals with HSAM, and all exhibit more sleep spindles—brief bursts of brainwave activity—than your average Joe.²⁸ 

While HSAM may be rare, it offers critical insights into how explicit memories—especially episodic ones—are formed, stored, and retrieved, which may be able to revolutionize memory rehabilitation methods. 

Constructive Memory

If you’re interested in learning more about how we recall information stored in our long-term memory—and why we sometimes make mistakes—check out this article about constructive memory. The article explains how prior knowledge, emotions, and new information all impact the way we remember past experiences, which can lead to distortions instead of exact copies. It also explores how the way that we construct memories can lead to unreliable eyewitness testimonies, but may also be responsible for our ability to imagine future events. 

Does Emotion Affect Our Ability to Make Rational Decisions?

One of the reasons that episodic memories are kept in our long-term storage is because of the strong emotions that accompany the personal experiences in our lives. We not only remember the event, but the emotion that we felt at the time as well. What this means is that when we recall the information when faced with a decision, the emotions that are conjured up may actually impact our decision. In this article, our writer Tiantian Li explores the role emotions play when we make decisions related to reward and enjoyment.

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