How memory works: encoding, storage and retrieval

Transcript

RyanImagine you're introduced to a man. You chat, step out of the room for a few minutes, and come back. He doesn't know you. He introduces himself again. And yet, when he's given the same puzzle several days in a row, he solves it faster every day.

SoheeHe has no memory of the puzzle. But some part of him clearly remembers how to do it.

RyanWelcome to EPPP Prep, the podcast. I'm Ryan.

SoheeI'm Sohee. That man was the famous patient known as H. M., and by the end of today you'll be able to explain exactly what he lost and what he kept. This is our first of two episodes on memory.

RyanStart with a definition. The OpenStax psychology textbook calls memory the set of processes used to encode, store and retrieve information over different periods of time. Encoding, storage, retrieval. Let's take them in order.

SoheeEncoding is the input of information into the memory system. Some of it happens through automatic processing, like details of time, space and frequency, usually without awareness. What you had for lunch, for instance.

RyanAnd some takes effortful processing, work and attention. Like the material you're studying right now.

SoheeThere are three types of encoding. Semantic encoding is encoding words and their meaning. Visual encoding is encoding images. Acoustic encoding is encoding sounds, words in particular.

RyanAn early demonstration of semantic encoding came from William Bousfield in 1935. People memorized sixty words that secretly fell into four categories, presented in random order. When they recalled them, they tended to recall them in categories. They'd paid attention to meaning.

SoheeAnd images help. Concrete, high-imagery words like car, dog and book are easier to recall than abstract words like truth and value, because they're encoded both visually and semantically.

RyanSo which type of encoding gives the best memory for words? Fergus Craik and Endel Tulving tested it in 1975. Participants answered questions about words that required visual, acoustic or semantic processing, then got an unexpected memory test.

SoheeVisual questions were about things like the font. Acoustic questions were about sound or rhyme. Semantic questions were about meaning. And the semantically encoded words were remembered best. Semantic encoding involves a deeper level of processing.

RyanWhich connects to Craik and Lockhart's levels of processing idea from 1972: the deeper you think about something, the better you remember it.

SoheeAnd the self-reference effect pushes that further. People tend to have better memory for information that relates to themselves than for material with less personal relevance.

RyanNow storage. The classic model is Atkinson and Shiffrin's from 1968. Information passes through three stages: sensory memory, short-term memory, and long-term memory.

SoheeSensory memory is very brief storage of sights, sounds and tastes, up to a couple of seconds. We can't absorb most of it. What we treat as valuable moves on to short-term memory.

RyanShort-term memory storage lasts fifteen to thirty seconds. And capacity? In 1956, George Miller reviewed the research and reported the magic number seven, plus or minus two. More contemporary research puts working memory capacity at four, plus or minus one.

SoheeWatch that pair. Seven plus or minus two is Miller, about short-term memory. Four plus or minus one is the more recent estimate, from Cowan, for working memory.

RyanTo move information from short-term to long-term memory, we rehearse. Active rehearsal is repeating the information. Elaborative rehearsal links new information to things you already know.

SoheeThen long-term memory, the continuous storage of information. Unlike short-term memory, its capacity is believed to be unlimited.

RyanAtkinson and Shiffrin aren't the only model. Baddeley and Hitch, in 1974, proposed working memory, where short-term memory has different forms.

SoheeThere's a visuospatial sketchpad for visual-spatial material, a phonological loop for spoken or written material, and an episodic buffer, which Baddeley added in 2000. And a central executive supervises the flow of information to and from those three systems, and moves information into long-term memory.

RyanAnd a subtle point the textbook makes. Short-term memory and working memory are sometimes used interchangeably, but they're not exactly the same. Short-term memory is more accurately described as a component of working memory.

SoheePause and think. A student is shown words and, for each one, asked, does this word describe you? Another student is asked, is this word in capital letters? Who remembers more, and which two ideas explain it?

RyanThe first student. Thinking about meaning is semantic encoding, a deeper level of processing. And relating the words to herself adds the self-reference effect. The capital letters question is shallow, visual encoding.

SoheeNow, long-term memory comes in two kinds. Explicit memories are those we consciously try to remember, recall and report. Explicit memory is also called declarative memory, because it can be put into words.

RyanExplicit memory divides into episodic and semantic. Episodic memory is about events we personally experienced, the what, where and when of an event. Your last birthday. Endel Tulving first proposed the concept in the 1970s.

SoheeSemantic memory is knowledge about words, concepts, and language-based facts. The definition of psychology. It's usually reported as facts, where episodic memory is usually reported as a story.

RyanImplicit memories are long-term memories that aren't part of our consciousness. You can't consciously recall them, but they show up in how you perform a task. There are several types.

SoheeProcedural memory, for skilled actions like riding a bicycle or driving. You're good at staying balanced, but you can't tell someone exactly how you do it.

RyanPriming, where exposure to one stimulus affects the response to a later one. Read a story about a picnic, and when you unscramble some letters, you're more likely to find the word plate.

SoheeThat works through semantic networks. Memories are organized in linked networks of concepts, and activating one part partly activates the linked concepts. That's spreading activation, from Collins and Loftus.

RyanAnd emotional conditioning, the memory behind classically conditioned emotional responses. A smell that makes you feel nostalgic, and you don't know why.

SoheeLast of the three processes: retrieval, getting information out of storage and back into awareness. There are three ways. Recall is accessing information without cues, like an essay test.

RyanRecognition is identifying information you've learned before when you meet it again. It involves comparison. A multiple-choice exam relies on recognition.

SoheeAnd relearning is learning something you previously learned. Someone who took Spanish years ago and finds she picks it back up surprisingly fast.

RyanNow the brain. Karl Lashley searched for the engram, the physical representation of a memory, by making lesions in rats' cortex after they learned a maze. The rats still found their way, regardless of the lesion's size or location.

SoheeToday the main areas linked with memory are the amygdala, the hippocampus, the cerebellum and the prefrontal cortex.

RyanThe amygdala is involved in fear and fear memories. And because it processes emotional information, it seems to help encode memories more deeply when an event is emotionally arousing.

SoheeThe hippocampus is associated with declarative and episodic memory and recognition memory, and it plays a part in consolidation, transferring new learning into long-term memory.

RyanThe cerebellum handles procedural memories, motor learning and classical conditioning. Rabbits with damaged cerebellums couldn't learn the conditioned eye-blink response. And the prefrontal cortex appears involved in semantic tasks.

SoheeWhich brings us back to H. M. Surgery to control his seizures removed both his left and right temporal lobes, the hippocampi, as the textbook puts it. Afterward he lost the ability to form new memories, but he could still remember events from before the surgery.

RyanThat's anterograde amnesia: you can't remember new information, but you can remember what happened before the injury. The hippocampus is usually affected. And many people with it can't form new episodic or semantic memories but can still form new procedural memories.

SoheeWhich explains the puzzle. H. M. didn't remember seeing it, but he got faster each day.

RyanRetrograde amnesia is the reverse: loss of memory for events before the trauma. People can't remember some or even all of their past, especially episodic memories.

SoheePause and think. After a car crash, a woman can't remember her wedding or anything from the years before the accident, but she easily learns the names of her new nurses. Which kind of amnesia?

RyanRetrograde. The memories lost are from before the injury, and new learning works. If she couldn't learn the nurses' names, that would point to anterograde.

SoheeSo, on the exam, the common traps are these pairs. Short-term versus working memory. Episodic versus semantic. Explicit versus implicit. Recall versus recognition. Anterograde versus retrograde. For each, ask the one question that separates them.

RyanLet's recap. Memory is encoding, storage and retrieval. Semantic encoding, deeper processing, beats visual and acoustic, and the self-reference effect helps even more.

SoheeAtkinson and Shiffrin: sensory, short-term, long-term. Miller's seven plus or minus two, and the newer four plus or minus one.

RyanBaddeley and Hitch: a central executive over the phonological loop, visuospatial sketchpad and episodic buffer.

SoheeExplicit memory is episodic and semantic. Implicit memory is procedural, priming and emotional conditioning. Retrieval is recall, recognition or relearning.

RyanHippocampus for new declarative memories. Amygdala for fear and emotional memories. Cerebellum for procedures and conditioned eye-blinks. H. M. lost the ability to make new explicit memories, but kept procedural learning.

SoheeAnd here's something encouraging from this very chapter. Relearning can go surprisingly fast, like it did for the woman picking her Spanish back up. If you studied this before and it feels rusty, you're not starting over.

RyanNext time, forgetting and false memory. Until then, try a few practice questions. See you on EPPP Prep.

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