8.1 How Memory Functions

   In the information-processing model of human memory, stimuli from the environment are processed first in sensory memory: storage of brief sensory events, such as sights, sounds, and tastes. Sensory memory is extremely limited in maintaining information—up to a couple of seconds before information is further categorized for what will be processed in the next stage, short-term memory. We are constantly bombarded with sensory information through transduction from our various types of sensory receptors. We cannot absorb all of this information, or even most of it, and each distinct level of memory process acts as a filter as information moves from sensory memory, to short-term, and finally long-term memory where information is available for later recall. For example, what was your professor wearing the last class period? As long as the professor was dressed appropriately, most of the time the attire of a professor is not readily important and therefore is not usually considered important enough to rehearse and store in long-term memory. Sensory information about sights, sounds, smells, and even textures, which we do not view as valuable information, we discard. Think about driving for an hour or so. You are obviously absorbing the information around you as you drive as is evident by your ability to properly navigate to your destination, however you will most likely not be able to remember small specific details about your drive such as how many blue cars you passed or the names of all the street signs you passed along the way. If we view something as valuable, the information will move into our short-term memory system, but most information we process is filtered out in order to allow us to focus on what we categorize as important.

One study of sensory memory investigated the significance of valuable information on short-term memory storage. In one of the more well know experimental designs in psychology, J. R. Stroop discovered a memory phenomenon in the 1930s: you will name a color more easily if it appears printed in that color, which is called the Stroop effect. In other words, the word “red” will be named more quickly, regardless of the color the word appears in, than any word that is colored red. Try an experiment: name the colors of the words you are given in the figure below. Do not read the words, but say the color the word is printed in. For example, upon seeing the word “yellow” in green print, you should say “green,” not “yellow.” This experiment is fun, and not as easy as it seems.

Figure 8.03. The Stroop effect describes why it is difficult for us to name a color when the word and the color of the word are different.

SHORT-TERM MEMORY

   Short-term memory (STM) represents a temporary storage system that processes incoming sensory memory. Although some argue for no distinction between short-term and working memory (Cowen, 2008; Rose, Myerson, Roediger & Hale, 2010), for the sake of consistency with other introductory psychology text (Licht, Hull & Ballantyne, 2014) we will consider short-term memory a stage in the information processing model as well as a location where information is stored, and working memory as a collection of processes that allow us to maintain and manipulate information. The ability to maintain information longer than what is provided by sensory memory within working memory allows for rehearsal strategies or meaning to be assigned to information ensuring later accurate recall.

Working memory capacity is limited and operates on a bottleneck model of information processing. The bottleneck analogy refers to the flow of information through memory beginning from the base of a hypothetical bottle where large amounts of information are being processes through the senses, and as information is processed in working memory, the amount of information that is able to pass through the narrowing neck of the bottle and on to long term memory is drastically reduced (through the narrow neck of the bottle) in stored information compared to what was initially processed at the encoding stage.  Working memory processes exist right where the bottle becomes narrow allowing us to maintain information in working memory for about 20 seconds which will make the information more likely to end up securely stored in long-term memory. George Miller (1956), in his research on the capacity of memory which aided in the dawn of the field of cognitive psychology, found that most people can retain about 7 items in STM. Some remember 5, some 9, so he called the capacity of STM 7 plus or minus 2.  More recent research re-evaluating working memory capacity suggests working memory capacity on average actually tends to be even lower at about four plus or minus one units of information suggesting a higher capacity found by Miller may have been related to the use of heuristics (discussed further below) such as chunking information (Cowan, 2001).

Think of short-term memory as the information you have displayed on your computer screen—a document, a spreadsheet, or a web page. Then, information in short-term memory goes to long-term memory (you save it to your hard drive), or it is discarded (you delete a document or close a web browser). The conscious repetition of information known as rehearsal allows information to move from the temporary short term memory store into long-term memory, a process known as memory consolidation.

You may find yourself asking, “How much information can our memory handle at once?” To explore the capacity and duration of your short-term memory, have a partner read the strings of random numbers below out loud to you, beginning each string by saying, “Ready?” and ending each by saying, “Recall,” at which point you should try to write down the string of numbers from memory.

Figure 6. Work through this series of numbers using the recall exercise explained above to determine the longest string of digits that you can store.

   Note the longest string at which you got the series correct. As noted above, revisions to Miller’s seven plus or minus two capacity suggest on average, most people will have a working memory capacity of about 4 plus or minus one units when not using any kind of memory technique such as chunking. Recall is somewhat better for random numbers than for random letters (Jacobs, 1887), and also often slightly better for information we hear (acoustic encoding) rather than see (visual encoding) (Anderson, 1969), but as discussed above, information processed with more depth of processing tend to be more readily available compared to more shallow encoding of information.

THEORIES OF WORKING MEMORY

In humans, working memory is composed of various organized processes and consists of at least two individual mechanisms used to maintain and manipulate verbal and visuospatial information, a mediating mechanism that blends the different forms of information, and an overarching attention allocating mechanism that focuses the use of cognitive resources between the sub divisions of working memory. This structured organization of working memory processes was first proposed by Baddeley and Hitch (1974) and was initially proposed to be made up of three different sub-systems known as the visuospatial sketchpad, the episodic buffer, and the phonological loop. These three sub-systems are then coordinated by an attention directing mechanism known as the central executive.

According to the Baddeley (2000; Baddeley & Hitch, 1994) model, the phonological loop is mainly concerned with the processing and maintenance of verbal and auditory information. This mechanism has also been likened to what we understand as our inner monologue, which we use to recite and rehearse information in order to build a strong trace for later recall. We use the phonological loop while reading, trying to solve problems in our head, or learning new vocabulary. Studies have suggested on average people are able to actively manipulate about two seconds worth of verbal information without relying on repetition rehearsal (Baddeley, 2002).

The visuospatial sketchpad on the other hand represents a mechanism separate from the phonological loop that allows for the maintenance and manipulation of visual and spatial information. This system allows us to navigate in a room without your sight, reaching out to grab your coffee without spilling it all over your brand new khakis, and also aids in manipulation of spatial perspective. Using the visuospatial sketchpad we are able to envision a map of campus and determine what path to take to get to a lecture you would like to attend, or alternate routes to take in order to avoid congested traffic. Studies examining the visuospatial sketchpad demonstrated individuals have trouble trying to perform two visuospatial tasks at the same time suggesting this aspect of working memory is fairly demanding in terms of cognitive resource load (Repovš & Baddeley, 2006).

The central executive represents an attention allocating mechanism. Similar to a group leader or manager of lower level workers, the central executive is the process of determining which information to focus on, and therefore which working memory to utilize. The central executive additionally decides which information to ignore, and also has a limited capacity which explains people become less productive at individual tasks when performing many different tasks at once (texting, while eating and driving at the same time). The Eriksen Flanker task represents a widely used method in cognitive science to quantify the ability of the central executive to quickly and accurately suppress distractors in their recognition and response to target cues (ignore distractions) (Eriksen & Eriksen, 1974).

LONG-TERM MEMORY

Long-term memory (LTM) is the continuous storage of information. Unlike short-term memory, the storage capacity of LTM has no limits. It encompasses all the things you can remember that happened more than just a few minutes ago to all of the things that you can remember that happened days, weeks, and years ago. In keeping with the computer analogy, the information in your LTM would be like the information you have saved on the hard drive. It isn’t there on your desktop (your short-term memory), but you can pull up this information when you want it, at least most of the time. Not all long-term memories are strong memories. Some memories can only be recalled through prompts. For example, you might easily recall a fact— “What is the capital of the United States?”—or a procedure—“How do you ride a bike?”—but you might struggle to recall the name of the restaurant you had dinner when you were on vacation in France last summer. A prompt, such as that the restaurant was named after its owner, who spoke to you about your shared interest in soccer, may help you recall the name of the restaurant.

Long-term memory is divided into two types: explicit and implicit. Understanding the different types is important because a person’s age or particular types of brain trauma or disorders can leave certain types of LTM intact while having disastrous consequences for other types.

Figure 8.05. There are two components of long-term memory: explicit and implicit. Explicit memory includes episodic and semantic memory. Implicit memory includes procedural memory and things learned through conditioning.

Explicit memories (also referred to as declarative memories) are those we consciously try to remember and recall. Explicit memory has to do with the storage of facts and events and is the type of memory you are aware of having and can consciously express. For example, if you are studying for your chemistry exam, the material you are learning will be part of your explicit memory. Explicit memory has two parts: semantic memory and episodic memory.

Semantic memory has to do with language and knowledge about language. An example would be the question “what does argumentative mean?” Stored in our semantic memory is knowledge about words, concepts, and language-based knowledge and facts. For example, answers to the following questions are stored in your semantic memory:

• Who was the first President of the United States?
• What is democracy?
• What is the longest river in the world?

Episodic memory is information about events we have personally experienced. The concept of episodic memory was first proposed about 40 years ago (Tulving, 1972). Since then, Tulving and others have looked at scientific evidence and reformulated the theory. Currently, scientists believe that episodic memory is memory about happenings in particular places at particular times, the what, where, and when of an event (Tulving, 2002). It involves recollection of visual imagery as well as the feeling of familiarity (Hassabis & Maguire, 2007).

Often our most vivid episodic memories are associated with intense emotions. A flashbulb memory is a highly detailed, exceptionally vivid episodic memory of the circumstances surrounding a piece of surprising, consequential, or emotionally arousing news was heard. With flashbulb memories, individuals often recall the precise moment you learned of the event and specific details around it- where you were, who or what source informed you, what you did next, and how you felt. Notably, flashbulb memories are not first-hand memories of experiencing the event but rather the experiences associated with learning about an event (Hirst & Phelps, 2016). In addition, while memories seem intense and vivid, research suggests flashbulb memories are prone to inaccuracies and may lack specific important details (Hirst et al., 2015).

Implicit memories (also referred to as non-declarative memories) are memories that are not part of our consciousness. They are memories formed from behaviors. A common example of implicit memory is represented by what is known as repetition priming. Repetition priming represents a general form of implicit memory where a previous encounter with information facilitates later processing of the same information (Ashcraft & Radvansky, 2013). Repetition priming has been documented in a number of tasks such as word identification and lexical decision making tasks (Morton, 1979), word and picture naming tasks (Brown et al., 1991), and rereading fluency tasks (Masson, 1984). Within all these studies, prior experience to the stimuli leads to faster performance on a later task, even if the individual does not remember having encountered the stimuli before.

A classic demonstration of repetition priming described by Jacoby and Dallas (1981) who asked participants to study a list of familiar words, answering a question about each word as they moved through the task. Sometimes the questions asked participants about the physical form of the word as in “does the word contain the letter r?”, sometimes participants were asked about the sound of the word as in “does the word rhyme with train?”, and sometimes participants were asked about semantic characteristics of the word as in “is the word in the center of the nervous system?”. Related to Craik and Lockharts depth of processing theories (1972), Asking participants about the physical form of the word should create shallow information processing, while asking about the sound should create deeper processing and semantic questions should create the deepest levels of information processing. After the information was encoded, explicit memory was tested using a simple recognition and recall task. This task demonstrated that recognition and recall was highest for information that was coded at the deepest levels (semantic encoding), while the shallow coded information was less available for recall and recognition. In the implicit memory task, participants were presented the words one at a time for only 35 ms, followed by a row of asterisks as a mask. Participants had to report the words they say, demonstrating that participants did not need to remember which words they had seen earlier, they just had to identify what words were very briefly presented. On average, word identification was about 80% regardless of how they had been studies, in comparison to 65% of control words that had not been previously presented. This is a typical finding in implicit memory tasks in that even without conscious recollection of the stimuli that had been previously presented, there is a faster and more accurate response for words that were previously presented compared to those that were not.

An additional important implicit memory tasks created by Blakemore (1977) demonstrates implicit learning processes in amnesic patients. Being that patients such as H.M. who experienced bilateral damage to the hippocampus and lateral temporal lobes, and was unable to form new memories (anterograde amnesia), these patients were asked to complete a drawing exercise where they were to trace in inside guiding lines, specific shapes while watching their hands move in a mirror. Initially, this task is extremely difficult showing participants have lots of trouble staying within the lines. However, amnesic patients who have no recollect of completing the task before show significant improvement over time demonstrating clear implicit processes related to learning and memory.

Figure 8.06. H.M., a patient with anterograde amnesia completes and motor learning task in a mirror over a series of days. Improvement in the task over time represents evidence of implicit learning and memory. (adapted from Kalat, 2015)

Procedural memory is a type of implicit memory: it stores information about how to do things where you are able to perform actions without consciously monitoring the sub procedures that need to be pieced together in order to perform the task. It is the memory for skilled actions, such as how to brush your teeth, how to drive a car, and how to swim. If you are learning how to swim freestyle, you practice the stroke: how to move your arms, how to turn your head to alternate breathing from side to side, and how to kick your legs. You would practice this many times until you become good at it. Once you learn how to swim freestyle and your body knows how to move through the water, you will never forget how to swim freestyle, even if you do not swim for a couple of decades. Similarly, if you present an accomplished guitarist with a guitar, even if he has not played in a long time, he will still be able to play quite well.

Emotional Conditioning is also a type of implicit memory. Memories acquired through classical conditioning are also categorized as implicit such as the feelings of hunger you get when smelling the aroma of favorite food truck while walking by. Associations are created implicitly between stimuli that commonly occur together cueing thoughts of the associated stimuli when the first is encountered. Evidence of implicit memory can be found in studies using priming procedures, which are processes where individuals are measured on how they improve at tasks when being cued below conscious experience on how to respond to a task. Implicit memory also contributes to the illusion-of-truth effect where individuals are more likely to rate statements of being true if they had previously experience that statement regardless of whether it is true or not.

CAN YOU REMEMBER EVERYTHING YOU EVER DID OR SAID?

   Episodic memories are also called autobiographical memories. Let’s quickly test your autobiographical memory. What were you wearing exactly five years ago today? What did you eat for lunch on April 10, 2009? You probably find it difficult, if not impossible, to answer these questions. Can you remember every event you have experienced over the course of your life—meals, conversations, clothing choices, weather conditions, and so on? Most likely none of us could even come close to answering these questions; however, American actress Marilu Henner, best known for the television show Taxi, can remember. She has an amazing and highly superior autobiographical memory.

 

Marilu Henner’s super autobiographical memory is known as hyperthymesia. (credit: Mark Richardson)

 

Very few people can recall events in this way; right now, only 12 known individuals have this ability, and only a few have been studied (Parker, Cahill & McGaugh 2006). And although hyperthymesia normally appears in adolescence, two children in the United States appear to have memories from well before their tenth birthdays.