Chapter 6: Introduction to Episodic Long-Term Memory

Episodic memory is akin to mental time travel, allowing individuals to recall specific personal events and experiences. Unlike semantic memory, which stores general knowledge about the world, episodic memory is unique to each individual. For example, remembering what happened when you passed your driver’s test involves episodic memory—you consciously bring the event into awareness, complete with its details, context, and emotional significance. This memory system allows us to revisit past experiences and imagine future scenarios. Episodic memories are richly integrated, drawing on sensory, motor, spatial, linguistic, and emotional information to form coherent recollections. Unlike semantic memory, which stores general knowledge like the concept of a driver’s license, episodic memory is uniquely tied to the personal context in which events occur, making it a cornerstone of our autobiographical history.

Definition and Characteristics

• Definition: Episodic memory involves remembering personal experiences, such as events, places, and times.
• Characteristics: It includes autobiographical details and the context in which events occurred.

Historical Perspective

• Endel Tulving's Contribution: Tulving proposed the term "episodic memory," asserting that it is unique to humans, though this view is debated due to evidence suggesting similar capabilities in some animals.

Dissociations and Case Studies

• Case of K.C.: Following a motorcycle accident, K.C. lost the ability to form new episodic memories, yet retained semantic memory abilities.
• Comparison with H.M. (and also Clive Wearing): These cases illustrate dissociations between episodic and semantic memories due to hippocampal damage.

The cases of K.C. and H.M. provide distinct insights into memory systems. Both individuals suffered from significant memory impairments, yet their conditions highlight different aspects of memory function. K.C., who lost his episodic memory due to damage to the medial temporal lobes and other regions, retained his semantic memory and could discuss general knowledge but had no ability to recall personal past experiences. So, KC can learn new facts (semantic memory) but he has no memory for when he learned this (episodic memory). In contrast, H.M., following surgical removal of parts of the medial temporal lobes, including the hippocampus, lost the ability to form any new long-term memories, whether episodic or semantic, though his older episodic memories remained intact. When conversing with them, both could engage in coherent discussions in the moment, supported by their preserved short-term memory. However, K.C. lacks any personal episodic recall, while H.M. retained vivid older episodic memories. These differences underscore how episodic and semantic memories rely on overlapping yet distinct neural mechanisms.

Encoding and Retrieval Processes

• Encoding: Involves the initial processing of sensory information into memory traces.
• Retrieval: Involves the recovery of stored episodic memories for conscious awareness.

Experimental Paradigms and Research Methods

Serial Position Effects

The serial position effect refers to the tendency for individuals to recall items from the beginning (primacy effect) and end (recency effect) of a list more accurately than those in the middle. This phenomenon reflects differences in memory processing: early items benefit from long-term memory encoding, while late items are still accessible in short-term memory. Research has shown that the primacy and recency effects are influenced by distinct cognitive and neural mechanisms.

Talmi et al. (2005) investigated the neural basis of the serial position effect using fMRI to distinguish between dual-store and single-store models of memory. Dual-store models of memory propose that short-term memory (STM) and long-term memory (LTM) are separate systems, with distinct mechanisms for encoding and retrieval. In contrast, single-store models suggest that both early and late items are processed by the same memory system, with differences in recall due to factors like discriminability or context. The results support dual-store models, showing that early list items activate brain regions associated with long-term memory (such as the hippocampus), while late items rely on short-term memory mechanisms (frontal cortex - including dorsolateral prefrontal cortex which is implicated in working memory). This evidence underscores the separability of memory processes for items at different serial positions and aligns with the traditional view of separate memory stores.

Francis Nipher, Ebbinghaus, and the History of Memory Research

Francis E. Nipher, primarily known as a physicist, made significant contributions to the study of memory, becoming one of the earliest researchers in this field. In 1876, Nipher observed what we now recognize as serial position effects—the tendency for people to better remember items at the beginning and end of a list while struggling with those in the middle. This insight came as he noticed his graduate students could more easily recall the first and last pieces of information from the data he presented during lectures.

Additionally, Nipher was a pioneer in developing a method remarkably similar to what later became known as the Brown-Peterson task (discussed in the STM chapter). This technique involves studying short-term memory by introducing a distraction task to prevent rehearsal before recall. His work laid foundational concepts for understanding memory processes, despite his primary career in physics.

Ebbinghaus conducted groundbreaking research on memory by studying his own recall of consonant-vowel-consonant (CVC) sequences, such as "ZUX" or "QAB," which were designed to be meaningless and minimize prior associations. He developed the concept of savings scores to quantify memory retention, measuring the reduction in time or effort needed to relearn previously studied material compared to the initial learning session. His findings revealed that most forgetting occurs shortly after initial study, with a steep decline in retention over time—a pattern now known as the forgetting curve. However, Ebbinghaus also showed that overlearning, or continuing to study material beyond the point of initial mastery, significantly improved long-term retention, making the material more resistant to forgetting. This work established foundational principles about memory and learning still recognized today.

Memory Enhancement Techniques

Levels of Processing

Shallow vs. Deep Processing

Craik and Lockhart proposed that the depth at which we process information determines its memorability. Shallow processing involves surface-level encoding, such as recognizing visual features or phonological characteristics without deeper meaning. In contrast, deep processing involves semantic encoding, where we connect new information with existing knowledge and meanings stored in long-term memory.

Evidence from Research

1. “G” word study. Craik and Watkins (1973) investigated whether the duration of time information spends in short-term memory leads to its transfer to episodic memory. To test this, they asked participants to remember all words that began with the letter "G." When participants encountered a "G" word, they were instructed to repeat it silently in their minds until the next "G" word appeared, allowing the researchers to control how long each word was rehearsed. The results showed that the length of time a word was repeated did not improve memory. This finding demonstrated that shallow, time-based rehearsal alone does not enhance memory retention, emphasizing the importance of deeper, more meaningful encoding processes.
2. Craik and Tulving's Experiment: Participants were presented with words and asked to process them at different levels (e.g., structural, phonemic, semantic). Semantic processing consistently resulted in better recall, demonstrating that deeper processing enhances memory retention (Craik & Tulving, 1975).
3. Generation Effect: Slamecka and Graf (1978) identified the generation effect, a phenomenon where information is better remembered when individuals generate it themselves rather than simply reading it. In their experiments, participants were asked to either read pairs of related words (e.g., "rapid-fast") or generate the second word based on a cue and a rule (e.g., "rapid-f_____," where participants would produce "fast"). The results consistently showed superior recall and recognition for words that were self-generated. This effect highlights the importance of active engagement and deeper cognitive processing in memory encoding, demonstrating that generating information enhances meaningful connections and improves retention compared to passive learning. In addition, a person does not even need to succeed in generating the to-be-remembered information. Instead, all they need to do is try. If people are given items like “antonym of trivial-v___” they will still have better memory than reading the answer if they give up and the researcher needs to supply them with the answer (vital).
4. Imagery and Memory: Concrete words that evoke mental images (e.g., "dog," "tree") are easier to remember than abstract words ("justice," "idea"). The dual-code hypothesis suggests that having both a verbal and visual code enhances memory because it provides multiple retrieval paths (Paivio, 1971). Some argue that having multiple codes makes this “deeper” than having a single verbal code.

Practical Applications

Educationally, encouraging students to engage in deep processing during learning—such as relating new information to personal experiences or actively generating examples—can enhance their retention and understanding of material. This approach contrasts with superficial rehearsal, which is less effective in fostering long-term memory.

Mnemonic Strategies

A mnemonic technique is a memory aid or strategy that helps improve the encoding, storage, and retrieval of information. These techniques often involve associating new information with familiar concepts, patterns, or structures to make it easier to remember. These techniques also provide a retrieval cue.

Method of Loci

The method of loci involves associating items to be remembered with specific locations in a familiar mental map, enhancing recall by leveraging spatial memory. For instance, if a person imagines walking across campus they could imagine broccoli holding open the doorway to a building and milk spilled on the walkway when they exit the building, etc (see Figure 6.1). This technique not only enhances recall by linking items to spatial map that is already stored in memory, but also provides a retrieval cue. Later, to remember the information, the person simply needs to imagine walking along the same mental map (when shopping at the store, the person could imagine walking across campus, using this mental map to help them easily remember items like broccoli, milk, and any other items they associate with specific locations along the way).

Figure 6.1. Visual depiction of the method of loci technique. Here a person imagines walking along a mental map like the Bates College campus and imagines broccoli holding open the doorway to a building (e.g., Pettengill Hall), milk spilled on the walkway, and bread on the college library. Later when they want to recall the list they simply need to mentally travel along the same path to facilitate memory.

"Depiction of the method of loci technique." by Kahan, T.A. is licensed under CC BY-NC-SA 4.0

Peg Word Mnemonic

Peg word mnemonic utilizes familiar sequences, like numbers, each associated with a rhyming word (e.g., "one is a bun, two is a shoe, three is a tree, etc"). Items to be remembered are then mentally associated with these words, facilitating recall through vivid imagery. For example, picturing broccoli stuck into a bun and milk in a shoe. Here, when the person is at the store they would recall one is a bun, two is a shoe, and then remember what was interacting with the bun and shoe to recall broccoli and milk.

Key Word Mnemonic

Key word mnemonic is particularly useful in learning languages, linking new words to familiar words in one's native language. For instance, associating "gato" (cat in Spanish) with "gate" by imagining a cat getting hit by a gate can aid recall by creating memorable associations that leverage semantic processing.

Link Method

The link method involves creating a mental chain linking items together sequentially, such as imagining broccoli (item 1) linked to milk (item 2), and so forth. So, the person might imagine broccoli sticking out of a glass of milk (see Figure 6.2). This method relies on visual imagery and associative thinking, where each item triggers the memory of the next, aiding in recall by reinforcing the sequential order of items. The downside of this method is that the retrieval cue is not already stored in memory in the same way a mental map might be (method of loci) or the numbers 1, 2, 3, etc (peg word).

Figure 6.2. Visual depiction of the link method. Here a person imagines each item on the list interacting. So, the person might imagine broccoli sticking out of a glass of milk followed by imagining milk being poured onto a loaf of bread. Later when they want to recall the list they need to recall these visual images that link the items together.

"Depiction of the link method." by Kahan, T.A. is licensed under CC BY-NC-SA 4.0

Invented Mnemonics

Invented mnemonics, like acronyms (e.g., SOHCAHTOA for trigonometry) or phrases (e.g., "My Very Excellent Mother Just Served Us Nachos" for planetary order), are effective in encoding and recalling information through creative and memorable word associations where the first letter of a memorized phrase provides a cue for recall. These mnemonics capitalize on elaborative processing and if the phrase is retrieved then the letters provide a cue for retrieval.

Task Effects in Episodic Memory

Recall vs. Recognition

Recall tasks require conscious recollection of information, such as fill-in-the-blank questions, where deep processing aids in retrieving specific details. In contrast, recognition tasks involve identifying previously learned information from a set of options (e.g., multiple-choice questions), where both conscious recollection and unconscious familiarity contribute to successful retrieval. Recognition tasks can improve with shallow processing, where a person circles an option that seems familiar, but deep-level processing still enhances recognition performance more than shallow processing.

Causes of Forgetting in Episodic Memory

Interference

Interference in episodic memory includes both proactive interference, where previously learned information disrupts the recall of newer information (e.g., difficulty learning "shoe goes with banana" after learning "shoe goes with pencil"), and retroactive interference, where newly learned information disrupts the recall of older information (e.g., difficulty recalling "shoe goes with pencil" after learning "shoe goes with banana"). These forms of interference contribute significantly to forgetting by disrupting the accessibility of memories rather than their decay over time.

Encoding Specificity

The theory of encoding specificity suggests that memory is influenced by the context in which information is learned. Rather than being stored as isolated facts, memories are encoded with the context surrounding them, such as the environment or emotional state at the time. For example, in Godden and Baddeley's (1975) classic experiment, divers learned a list of words either on land or underwater, and their recall was better when they were tested in the same environment where they learned the words (see Figure 6.3). This illustrates transfer appropriate processing, which is the finding that reinstating the original context, such as returning to a room where you forgot your purpose, can trigger memory. Memory retrieval is facilitated when the processes engaged during retrieval match those engaged during encoding. This principle also applies to various cues, such as visual, verbal, or even sensory cues like smells, which can help retrieval. Additionally, mood congruence and state-dependent learning show that memories are more easily recalled when the emotional or physical state at retrieval matches that of encoding, such as recalling happy memories when in a good mood or recalling information learned while intoxicated when in the same state.

Figure 6.3. Results from Godden and Baddeley's (1975) experiment show that memory is best when the study location matches the testing location. So here memory is best when learning takes place on land and the recall also takes place on land, or when both learning and recall take place under water.

"Depiction of the results from Godden and Baddeley." by Kahan, T.A. is licensed under CC BY-NC-SA 4.0

TAP or LOP

Memory is often better when the context at retrieval matches the context during study, which may explain why deeper study leads to better recall. This is because most tests assess the meaning of information, rather than surface-level details. Therefore, memory is strongest when information is studied with meaning in mind. On the other hand, if a test focuses on surface-level features, such as the sound of words, memory will be better when the study also involves those features. This idea aligns with the theory of transfer-appropriate processing, which suggests that memory performance improves when the study method matches the type of test. This could explain why deep-level processing often leads to better performance (which is the basis of levels of processing), it is NOT the deep processing that improves memory. Instead, deep processing at study is good because this method of studying aligns with the nature of most memory tests.

Episodic memories and negative priming

• Negative Priming: Initially thought to be caused by inhibition, W. Trammell Neill (who goes by Tram) proposed that negative priming might actually be due to memory retrieval processes. Negative priming refers to the phenomenon where people are slower to respond to something they recently ignored. Neill's perspective suggests that this effect occurs because the retrieved information (to ignore) is inappropriate for the current task demands. This is similar to the theory of transfer appropriate processing but rather than the memory facilitating performance, in some situation’s memory retrieval may hurt performance. For example, if a person is shown the word RED written in the color blue and are instructed to ignore the word and respond to the color, they may store in memory “don’t say red” (see Figure 6.4). Later, if the person is shown the word GREEN written in red they will be slow if they retrieve this memory. Here, retrieval of the memory “don’t say red” is inappropriate and hurts performance.

Figure 6.4. Depiction of a memory-based account of negative priming in the Stroop experiment. Rather than the person inhibiting the distractor word, the person may form a memory that they should not respond to the distractor word. If this memory is later retrieved then performance may be worse (i.e., slower reaction times and worse accuracy).

"Depiction of a memory-based account of negative priming." by Kahan, T.A. is licensed under CC BY-NC-SA 4.

• Experimental Evidence: Neill conducted an experiment where he manipulated the time between the prime and probe, known as the response-stimulus interval (RSI). Memories are typically easier to retrieve when they are closer in time because it's easier to remember recent events than those that occurred further in the past. Neill fully randomized the RSI, with some trials having a short RSI and others having a long one. As a result, the preceding RSI (PRSI) also varied, sometimes being long and sometimes short. Neill found that memories were more distinguishable and memorable when the PRSI was long, even for older memories, compared to when the PRSI was short. In other words, memories are easiest to retrieve when the RSI is short and the PRSI is long, and hardest when the RSI is long and the PRSI is short (see Figure 6.5). In cases of short-short or long-long RSI-PRSI pairings, memory retrieval was intermediate. Neill’s negative priming experiment showed that negative priming was strongest when the prime trial was easiest to retrieve from memory (short RSI and long PRSI), and weakest when the prime trial was harder to retrieve (long RSI and short PRSI). This suggests that negative priming may be linked to memory retrieval (see Figure 6.6). Neill has also demonstrated that negative priming is more pronounced when the context of the prime and probe trials match, further supporting the idea that episodic memory retrieval plays a role in negative priming. According to this view, nothing is actually inhibited in negative priming; rather, it is the retrieval of irrelevant information that impairs current performance.

Figure 6.5. Memories are easiest to retrieve when the RSI is short and the PRSI is long (labeled good in the figure), and hardest when the RSI is long and the PRSI is short (labeled bad in the figure).

"Depiction of how the time between the prime and probe can affect memory." by Kahan, T.A. is licensed under CC BY-NC-SA 4.0 

Figure 6.6. Results from experiments that manipulate both the RSI and PRSI. Negative priming is greatest when memory retrieval is easy (short RSI and long PRSI) and reduced when memory retrieval is difficult (long RSI and short PRSI). This supports the memory-based account of negative priming.

"Results from experiments where negative priming is shown to be affected by both the RSI and PRSI." by Kahan, T.A. is licensed under CC BY-NC-SA 4.0

• Debate and Consensus: There is ongoing debate between Neil's view of negative priming as related to memory retrieval versus other theories emphasizing inhibition. However, many researchers now acknowledge that both mechanisms likely play a role, with memory retrieval explaining some aspects of negative priming.