Types of Memory

Sensory Memory

Sensory memory allows an individual to remember an input in great detail but for only a few milliseconds.

Learning Objectives

Describe the different types of sensory memory

Key Takeaways

Key Points

  • Sensory memory allows individuals to recall great detail about a complex stimulus immediately following its presentation.
  • There are different types of sensory memory, including iconic memory, echoic memory, and haptic memory.
  • In sensory memory, no manipulation of the incoming information occurs, and the input is quickly transferred to the working memory.

Key Terms

  • sensory memory: The brief storage (in memory) of information experienced by the senses; typically only lasts up to a few seconds.
  • iconic: Visually representative.
  • echoic: Imitative of a sound; onomatopoeic.

Sensory memory allows individuals to retain impressions of sensory information for a brief time after the original stimulus has ceased. It allows individuals to remember great sensory detail about a complex stimulus immediately following its presentation. Sensory memory is an automatic response considered to be outside of cognitive control. The information represented in this type of memory is the "raw data" which provides a snapshot of a person's overall sensory experience. Information from sensory memory has the shortest retention time, ranging from mere milliseconds to five seconds. It is retained just long enough for it to be transferred to short-term (working) memory.

In sensory memory, no manipulation of the incoming information occurs as it is transferred quickly to working memory. The amount of information is greatly reduced during this transfer because the capacity of working memory is not large enough to cope with all the input coming from our sense organs.

Types of Sensory Memory

It is assumed that there is a subtype of sensory memory for each of the five major senses (touch, taste, sight, hearing, and smell); however, only three of these types have been extensively studied: echoic memory, iconic memory, and haptic memory.

Iconic Memory

Sensory input to the visual system goes into iconic memory, so named because the mental representations of visual stimuli are referred to as icons. Iconic memory has a duration of about 100 ms. One of the times that iconic memory is noticeable is when we see "light trails." This is the phenomenon when bright lights move rapidly at night and you perceive them as forming a trail; this is the image that is represented in iconic memory.


Light trails: In iconic memory, you perceive a moving bright light as forming a continuous line because of the images retained in sensory memory for milliseconds.

Echoic Memory

Echoic memory is the branch of sensory memory used by the auditory system. Echoic memory is capable of holding a large amount of auditory information, but only for 3–4 seconds. This echoic sound is replayed in the mind for this brief amount of time immediately after the presentation of the auditory stimulus.

Haptic Memory

Haptic memory is the branch of sensory memory used by the sense of touch. Sensory receptors all over the body detect sensations like pressure, itching, and pain, which are briefly held in haptic memory before vanishing or being transported to short-term memory. This type of memory seems to be used when assessing the necessary forces for gripping and interacting with familiar objects. Haptic memory seems to decay after about two seconds. Evidence of haptic memory has only recently been identified and not as much is known about its characteristics compared to iconic memory.

Short-Term and Working Memory

Short-term memory, which includes working memory, stores information for a brief period of recall for things that happened recently.

Learning Objectives

Compare short-term memory and working memory

Key Takeaways

Key Points

  • Short-term memory acts as a scratchpad for temporary recall of information being processed. It decays rapidly and has a limited capacity.
  • Rehearsal and chunking are two ways to make information more likely to be held in short-term memory.
  • Working memory is related to short-term memory. It contains a phonological loop that preserves verbal and auditory data, a visuospatial scratchpad that preserves visual data, and a central manager that controls attention to the data.

Key Terms

  • chunking: The splitting of information into smaller pieces to make reading and understanding faster and easier.
  • encoding: The process of converting information into a construct that can be stored within the brain.
  • consolidation: A process that stabilizes a memory trace after its initial acquisition.

Short-term memory is the capacity for holding a small amount of information in an active, readily available state for a brief period of time. It is separate from our long-term memory, where lots of information is stored for us to recall at a later time. Unlike sensory memory, it is capable of temporary storage. How long this storage lasts depends on conscious effort from the individual; without rehearsal or active maintenance, the duration of short-term memory is believed to be on the order of seconds.

Capacity of Short-Term Memory

Short-term memory acts as a scratchpad for temporary recall of information. For instance, in order to understand this sentence you need to hold in your mind the beginning of the sentence as you read the rest. Short-term memory decays rapidly and has a limited capacity.

The psychologist George Miller suggested that human short-term memory has a forward memory span of approximately seven items plus or minus two. More recent research has shown that this number is roughly accurate for college students recalling lists of digits, but memory span varies widely with populations tested and with material used.

For example, the ability to recall words in order depends on a number of characteristics of these words: fewer words can be recalled when the words have longer spoken duration (this is known as the word-length effect) or when their speech sounds are similar to each other (this is called the phonological similarity effect). More words can be recalled when the words are highly familiar or occur frequently in the language. Chunking of information can also lead to an increase in short-term memory capacity. For example, it is easier to remember a hyphenated phone number than a single long number because it is broken into three chunks instead of existing as ten digits.

Rehearsal is the process in which information is kept in short-term memory by mentally repeating it. When the information is repeated each time, that information is re-entered into the short-term memory, thus keeping that information for another 10 to 20 seconds, the average storage time for short-term memory. Distractions from rehearsal often cause disturbances in short-term memory retention. This accounts for the desire to complete a task held in short-term memory as soon as possible.

Working Memory

Though the term "working memory" is often used synonymously with "short-term memory," working memory is related to but actually distinct from short-term memory. It holds temporary data in the mind where it can be manipulated. Baddeley and Hitch's 1974 model of working memory is the most commonly accepted theory of working memory today. According to Baddeley, working memory has a phonological loop to preserve verbal data, a visuospatial scratchpad to control visual data, and a central executive to disperse attention between them.

Phonological Loop

The phonological loop is responsible for dealing with auditory and verbal information, such as phone numbers, people's names, or general understanding of what other people are talking about. We could roughly say that it is a system specialized for language. It consists of two parts: a short-term phonological store with auditory memory traces that are subject to rapid decay, and an articulatory loop that can revive these memory traces. The phonological store can only store sounds for about two seconds without rehearsal, but the auditory loop can "replay them" internally to keep them in working memory. The repetition of information deepens the memory.

Visuospatial Sketchpad

Visual and spatial information is handled in the visuospatial sketchpad. This means that information about the position and properties of objects can be stored. The phonological loop and visuospatial sketchpad are semi-independent systems; because of this, you can increase the amount you can remember by engaging both systems at once. For instance, you might be better able to remember an entire phone number if you visualize part of it (using the visuospatial sketchpad) and then say the rest of it out loud (using the phonological loop).

Central Executive

The central executive connects the phonological loop and the visuospatial sketchpad and coordinates their activities. It also links the working memory to the long-term memory, controls the storage of long-term memory, and manages memory retrieval from storage. The process of storage is influenced by the duration in which information is held in working memory and the amount that the information is manipulated. Information is stored for a longer time if it is semantically interpreted and viewed with relation to other information already stored in long-term memory.

Transport to Long-Term Memory

The process of transferring information from short-term to long-term memory involves encoding and consolidation of information. This is a function of time; that is, the longer the memory stays in the short-term memory the more likely it is to be placed in the long-term memory. In this process, the meaningfulness or emotional content of an item may play a greater role in its retention in the long-term memory.

This greater retention is owed to an enhanced synaptic response within the hippocampus, which is essential for memory storage. The limbic system of the brain (including the hippocampus and amygdala) is not necessarily directly involved in long-term memory, but it selects particular information from short-term memory and consolidates these memories by playing them like a continuous tape.

Long-Term Memory

Long-term memory is used for the storage of information over long periods of time, ranging from a few hours to a lifetime.

Learning Objectives

Contrast the different ways memories can be stored in long-term memory

Key Takeaways

Key Points

  • Long-term memory is the final, semi-permanent stage of memory; it has a theoretically infinite capacity, and information can remain there indefinitely.
  • Long-term memories can be categorized as either explicit or implicit memories.
  • Explicit memories involve facts, concepts, and events, and must be recalled consciously.
  • Explicit memories can be either semantic (abstract, fact-based) or episodic (based on a specific event).
  • Implicit memories are procedures for completing motor actions.

Key Terms

  • long-term memory: Memory in which associations among items are stored indefinitely; part of the theory of a dual-store memory model.
  • script: A "blueprint" or routine for dealing with a specific situation.

If we want to remember something tomorrow, we have to consolidate it into long-term memory today. Long-term memory is the final, semi-permanent stage of memory. Unlike sensory and short-term memory, long-term memory has a theoretically infinite capacity, and information can remain there indefinitely. Long-term memory has also been called reference memory, because an individual must refer to the information in long-term memory when performing almost any task. Long-term memory can be broken down into two categories: explicit and implicit memory.

Explicit Memory

Explicit memory, also known as conscious or declarative memory, involves memory of facts, concepts, and events that require conscious recall of the information. In other words, the individual must actively think about retrieving the information from memory. This type of information is explicitly stored and retrieved—hence its name. Explicit memory can be further subdivided into semantic memory, which concerns facts, and episodic memory, which concerns primarily personal or autobiographical information.

Semantic Memory

Semantic memory involves abstract factual knowledge, such as "Albany is the capital of New York." It is for the type of information that we learn from books and school: faces, places, facts, and concepts. You use semantic memory when you take a test. Another type of semantic memory is called a script. Scripts are like blueprints of what tends to happen in certain situations. For example, what usually happens if you visit a restaurant? You get the menu, you order your meal, you eat it, and then you pay the bill. Through practice, you learn these scripts and encode them into semantic memory.

Episodic Memory

Episodic memory is used for more contextualized memories. They are generally memories of specific moments, or episodes, in one's life. As such, they include sensations and emotions associated with the event, in addition to the who, what, where, and when of what happened. An example of an episodic memory would be recalling your family's trip to the beach. Autobiographical memory (memory for particular events in one's own life) is generally viewed as either equivalent to, or a subset of, episodic memory. One specific type of autobiographical memory is a flashbulb memory, which is a highly detailed, exceptionally vivid "snapshot" of the moment and circumstances in which a piece of surprising and consequential (or emotionally arousing) news was heard. For example, many people remember exactly where they were and what they were doing when they heard of the terrorist attacks on September 11, 2001. This is because it is a flashbulb memory.

Semantic and episodic memory are closely related; memory for facts can be enhanced with episodic memories associated with the fact, and vice versa. For example, the answer to the factual question "Are all apples red?" might be recalled by remembering the time you saw someone eating a green apple. Likewise, semantic memories about certain topics, such as football, can contribute to more detailed episodic memories of a particular personal event, like watching a football game. A person that barely knows the rules of football will remember the various plays and outcomes of the game in much less detail than a football expert.

Implicit Memory

In contrast to explicit (conscious) memory, implicit (also called "unconscious" or "procedural") memory involves procedures for completing actions. These actions develop with practice over time. Athletic skills are one example of implicit memory. You learn the fundamentals of a sport, practice them over and over, and then they flow naturally during a game. Rehearsing for a dance or musical performance is another example of implicit memory. Everyday examples include remembering how to tie your shoes, drive a car, or ride a bicycle. These memories are accessed without conscious awareness—they are automatically translated into actions without us even realizing it. As such, they can often be difficult to teach or explain to other people. Implicit memories differ from the semantic scripts described above in that they are usually actions that involve movement and motor coordination, whereas scripts tend to emphasize social norms or behaviors.

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