The model in Figure, developed by Richard Atkinson and Richard Shiffrin (1968) and subsequently modified, depicts memory as having three major components: sensory memory, working (short-term) memory, and long-term memory. Other models have been proposed, but this three-stage framework has been the most influential.
1. Sensory Memory:
Sensory memory briefly holds incoming sensory information. It comprises different subsystems, called sensory registers, which are the initial information processors. Our visual sensory register is called the iconic store, and in 1960 George Sperling conducted a classic experiment to assess how long it holds information.
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On one task, Sperling arranged 12 letters in three rows and four columns. He flashed the array on a screen for 1/20 of a second, after which participants immediately recalled as many letters as they could. Typically, they were able to recall only 3 to 5 letters.
Figure:
The three stage model of memory. In this model, memory has three major components: (1) sensory memory, which briefly holds incoming sensory information; (2) working (short term) memory, which processes certain information received from sensory memory and information retrieved from long term memory; and (3) long-term memory, which stores information for longer periods of time.
Why was recall so poor? Did participants have too little time to scan all the letters, or had they seen the whole array, only to have their iconic memory fade before they could report all the letters? To find out, Sperling conducted another experimental condition. This time, just as the letters were flashed off, participants heard either a high-, medium-, or low-pitched tone, which signaled them to report either the top, middle, or bottom row of letters.
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In this case, participants often could report all 4 letters in whichever row was signaled. They’re not knowing which row would be signaled ahead of time implies that their iconic memory had stored an image of the whole array, and they now had time to “read” their iconic image of any one line before it rapidly disappeared.
If this logic is correct, then participants should have done poorly if the signaling tone was delayed. Indeed, with just a 1 -second delay, performance was no better than without the tone. It is difficult, perhaps impossible, to retain complete information in purely visual form for more than a fraction of a second. In contrast, our auditory sensory register, called the echoic store, can hold information about the precise details of a sound for several seconds.
2. Short-Term Memory:
Most information in sensory memory rapidly fades away. But according to the original three stage model, through selective attention some information enters short-term memory, a memory store that temporarily holds a limited amount of information.
Memory Codes:
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Once information leaves sensory memory, it must be represented by some type of code if it is to be retained in short-term memory. For example, the words that someone just spoke to you (“I like your new haircut”) must somehow become represented in your mind. Memory codes are mental representations of some type of information or stimulus, and they can take various forms.
We may try to form mental images (visual codes), code something by sound (phonological codes), or focus on the meaning of a stimulus (semantic codes). For physical actions, such as learning sports or playing musical instruments, we code patterns of movement (motor codes).
The form of a memory code often does not correspond to the form of the original stimulus. As you read these words (visual stimuli) you are probably not storing images of the way the letters look. Rather, you are likely forming phonological codes (as you say the words silently) and semantic codes (as you think about their meaning). Thus when people are presented with lists of words or letters and asked to recall them immediately, they often make phonetic errors. They might mistakenly recall a V as a B because of the similarity in how the letters sound.
Capacity and Duration:
Short-term memory can hold only a limited amount of information at a time. Depending on the stimulus, such as a series of unrelated numbers or letters, most people can hold no more than five to nine meaningful items in short-term memory, leading George Miller to set the capacity limit at “the magical number seven, plus or minus two.” To demonstrate this, try administering the digit-span test to some people you know.
If short-term memory capacity is so limited, how can we remember and understand sentences as we read? For a partial answer, read the letters below (one per second); then cover them up and write down as many letters as you can remember, in the order presented.
Bircderykaeuqsasawti:
Did you have any trouble? Now, with the order of the letters reversed (and a few spaces added), try to remember all 20 letters.
It was a Squeaky Red Crib:
No doubt you found the second task much easier. The limit on short-term storage capacity concerns the number of meaningful units that can be re-called, and the 20 letters have been combined into 6 meaningful units (words). Combining individual items into larger units of meaning is called chunking, which aids recall.
Short-term memory is limited in duration as well as capacity. Have you ever been introduced to someone and then, moments later, realized that you’ve forgotten her or his name? Without rehearsal, information in short-term memory generally has a shelf life of up to 20 seconds. However, by rehearsing information such as when you look up a telephone number and keep saying it to yourself while waiting to use a phone you can extend its duration in short-term memory.
Putting Short-Term Memory to Work:
The original three-stage model viewed short-term memory as a temporary holding station along the route from sensory to long-term memory. Information that remained in short-term memory long enough presumably was transferred into more permanent storage. Cognitive scientists now reject this view as too passive.
Instead, they view short-term memory as working memory, a limited-capacity system that temporarily stores and processes information. In other words, working memory is a mental workspace that stores information, actively manipulates it, and supports other cognitive functions such as problem solving and planning.
Components of Working Memory According to one influential model, working memory has several components. One component, the phonological loop, briefly stores mental representations of sounds.
The phonological loop is active when you listen to a spoken word or when you sound out a word to yourself as you read. Silently repeating the name of person to whom you’re being introduced will briefly refresh the acoustic codes stored in the phonological loop.
A second component, the visuospatial sketchpad, briefly stores visual and spatial information, as occurs when you form a mental image of someone’s face or of the spatial layout of your bedroom. Note that the phonological loop and visuospatial sketchpad can be active simultaneously. For example, you can silently repeat the word sunset while at the same time holding a mental image of a sunset or, for that matter, of an elephant.
A third component, called the episodic buffer provides a temporary storage space where information from long-term memory and from the phonological and/or visuospatial subsystems can be integrated, manipulated, and made available for conscious awareness.
For example, after reading or hearing me say “How much is 87 plus 36?” your phonological loop initially maintains the acoustic codes for the sounds of 87 and 36 in working memory Your visuospatial sketchpad also might maintain a mental image of the numbers.
But to do this task, the rules for performing addition must be retrieved from your long-term memory and temporarily stored in the episodic buffer, where they are integrated with (i.e., applied to) information from the phonological and visuospatial subsystems. This creates the ingredients for the conscious perceptions that you experience as you perform the mental addition (e.g., “7+ 6=13, carry the 1 …”).
The episodic buffer also comes into play when you chunk information. British psychologist Alan Baddeley notes that despite the phonological loops very limited acoustic storage capacity people can routinely listen to and then repeat novel sentences that are 15 or 16 words long.
It is within the episodic buffer, he proposes, that groups of words are chunked into meaningful phrases and stored (and phrases can be further chunked into sentences), enabling us to recall relatively long sections of prose.
The fourth component of working memory, called the central executive, directs the overall action. When solving arithmetic problems, for example, the central executive doesn’t store the numbers or rules of addition. Instead, it plans and controls the sequence of actions that need to be performed, divides and allocates attention to the other subsystems, and integrates information within the episodic buffer. It also may monitor the progress as interim steps are completed.
3. Long-Term Memory:
Long-term memory is our vast library of more durable stored memories. Perhaps there have been times in your life, such as periods of intensive study during final exams, when you have felt as if there is no room for storing so much as one more new fact inside your brain. Yet as far as we know, long-term storage capacity essentially is unlimited, and once formed, a long-term memory can endure for up to a lifetime.
Is short-term and long-term memory really distinct? Case studies of amnesia victims like H. M. suggest so. If you told H. M. your name or some fact, he could remember it briefly but could not form a long-term memory of it. Experiments in which people with normal memory learn lists of words also support this distinction.
Suppose that we present you with a series of 15 unrelated words, one word at a time. Immediately after seeing or hearing the last word, you are to recall as many words as you can, in any order you wish. Most experiments find that words at the end and beginning of a list are the easiest to recall.
This U- shaped pattern is called the serial position effect, meaning that the ability to recall an item is influenced by the item’s position in a series. The serial position effect has two components: a primacy effect, reflecting the superior recall of the earliest items, and a recency effect, representing the superior recall of the most recent items.
What causes the primacy effect? According to the three-stage model, as the first few words enter short-term memory, we can quickly rehearse them and transfer them into long-term memory. However, as the list gets longer, short- term memory rapidly fills up and there are too many words to keep repeating before the next word arrives.
Therefore, beyond the first few words, it is harder to rehearse the items and they are less likely to get transferred into long-term memory. If this hypothesis is correct, then the primacy effect should decrease if we are prevented from rehearsing the early words, say by being presented the list at a faster rate. Indeed, this is what happens.
As for the recency effect, the last few words still linger in short-term memory and have the benefit of not being bumped out by new information. Thus if we try to recall the list immediately, all we have to do is recite the last words from short-term memory before they decay (i.e., fade away). In sum, according to the three- stage model, the primacy effect is due to the transfer of early words into long-term memory, whereas the recency effect is due to the continued presence of information in short-term memory.
If this explanation is correct, then it must be possible to wipe out the recency effect—but not the primacy effect by eliminating the last words from short-term memory. This happens when the recall test is delayed, even for as little as 15 to 30 seconds, and we are prevented from rehearsing the last words. To prevent rehearsal, we might be asked to briefly count a series of numbers immediately after the last word is presented.
Now by the time we try to recall the last words, they will have faded from short-term memory or been bumped out by the numbers task (6 … 7 … 8 … 9 …), under delayed conditions, the recency effect disappears while the primacy effect remains.
Having examined some basic components of memory, let us now explore more fully how information is encoded, stored, and retrieved.
Semantic and Episodic Memory:
The term Semantic memory was for the first time used by Quillian.
Semantic memory is one type of long term memory; semantic memory consists of knowledge about what words mean, about the ways they are related to one another and about the rules for using them in communication and thinking. In short it is a kind of memory which makes our use of language possible. Semantic memory is organised knowledge about the world including the verbal world of words and how they are used. Semantic memory consists of facts, principles, relations and strategies.
Information seems to stored in the semantic memory in a highly organised way. For instance, some experiments have indicated that information is stored in logical hierarchies that go from general categories to specific, ones. Such organisations make it possible for us to make logical inferences from the information stored in semantic memory. Other experiments have led to the idea that semantic memory is organised into clusters of words with related meanings.
The term episodic memory was used by Endel Tulving. Episodic memory consists of long term memories of specific thing that happened to us at particular times and places.
Episodic memory is memory for temporarily dated, autobiographical events in the individual’s own life. Episodic memories are tied to time and place. Thus, episodic memory are memories of episodes, long or short, in our own lives, they are dated and have a biographical reference. In other words our “remembrances of past” make up our episodic memory.
Episodic memory do not have a logical organisation. Episodic memory cannot help us to draw inferences.