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Memory storage is what allows people to retain information for future use. The various memory storage systems – sensory memory, short-term memory, and long-term memory – each differ in duration, capacity, and type of content they hold.
Sensory memory stores incoming sensory information in detail but only for an instant. The capacity of sensory memory is very large, but the information in it is unprocessed. If a flashlight moves quickly in a circle inside a dark room, people will see a circle of light rather than the individual points through which the flashlight moved. This happens because sensory memory holds the successive images of the moving flashlight long enough for the brain to see a circle. Visual sensory memory is called iconic memory; auditory sensory memory is called echoic memory.
Some of the information in sensory memory transfers to short-term memory, which can hold information for approximately 20 seconds. Rehearsing can help keep information in short-term memory longer. When people repeat a new phone number over and over to themselves, they are rehearsing it and keeping it in short-term memory.
Short-term memory has a limited capacity: it can store about seven pieces of information, plus or minus two pieces. These pieces of information can be small, such as individual numbers or letters, or larger, such as familiar strings of numbers, words, or sentences. A method called chunking can help to increase the capacity of short-term memory. Chunking combines small bits of information into bigger, familiar pieces.
Example: A person confronted with this sequence of 12 letters would probably have difficulty remembering it 10 seconds later, because short-term memory cannot handle 12 pieces of information: HO TB UT TE RE DP OP CO RN IN AB OW L However, these letters can be easily remembered if they are grouped into six familiar words, because short-term memory can hold six pieces of information: HOT BUTTERED POPCORN IN A BOWL
Information can be transferred from short-term memory to long-term memory and from long-term memory back to short-term memory. Long-term memory has an almost infinite capacity, and information in long-term memory usually stays there for the duration of a person’s life. However, this doesn’t mean that people will always be able to remember what’s in their long-term memory—they may not be able to retrieve information that is there.
Memory Storage Details
The following table summarizes memory storage details:
|
Type of Memory |
Duration |
Capacity |
Content |
|
Sensory Memory |
A few milliseconds to a couple of seconds |
Large but fleeting |
Iconic and echoic |
|
Iconic Memory |
About one second |
Large |
Visual stimuli |
|
Echoic Memory |
Up to several seconds |
Large |
Auditory stimuli |
|
Short-term Memory |
About 20 seconds |
About 7 items, +/- 2 |
Immediate conscious processing (e.g. words, numbers) |
|
Working Memory |
Temporary, dynamic |
Limited |
Manipulation of visual, auditory, or spatial information |
|
Long-term Memory |
Up to a lifetime |
Unlimited |
Facts, experiences, skills, and knowledge |
Enhancing Memory Storage
Storage can be enhanced through various techniques:
Maintenance rehearsal is a process of repeatedly reviewing or repeating information to retain it in short-term memory. This is effective for short-term memory storage but does not guarantee that the information will be stored in long-term memory.
Elaborative rehearsal strengthens long-term storage by associating new information with meaningful concepts or personal experiences.
Hyperthymesia (HSAM)
Some people have hyperthymesia, also known as highly superior autobiographical memory (HSAM), which allows them to recall events from their lives with incredible detail. Researchers have identified two tell-tale characteristics of this condition: an exceptional ability to recall details from one’s past and spending an excessive amount of time thinking about one’s past. Autobiographical memories have to do with personal experiences and the self, so they tend to be more vivid and easier to recall due to their emotional and personal significance, even for those without hyperthymesia. HSAM is extremely rare, with fewer than 100 known cases worldwide, which makes it difficult to study and understand.
Researchers suspect that neurological differences, such as an enlarged temporal lobe (involved in memory storage) and an enlarged caudate nucleus (linked to procedural memory), may explain this condition. The caudate nucleus also plays a role in habits and compulsive behaviors, potentially linking HSAM to obsessive tendencies. Interestingly, in some cases, brain scans of individuals with HSAM seem to resemble those of individuals with obsessive-compulsive disorder, suggesting that the above-average memory retention may, in part, be due to obsessive rehearsal, though further research is needed to understand this component.
In other cases, individuals with HSAM do not display obsessive tendencies and are still able to recall events from their past with remarkable detail and accuracy. Some studies suggest these individuals still show structural differences in the brain, particularly in areas involved in memory storage, such as the temporal lobe and hippocampus, but without the enlarged caudate nucleus seen in those with obsessive tendencies. This suggests that their memory retention may depend more on brain structures related to the formation and retrieval of memories rather than on repetitive mental rehearsal.
Memory Storage Impairment
Certain conditions can negatively affect memory storage processes. The following conditions demonstrate how memory storage can be disrupted by both physical impairments (such as brain damage) and developmental limitations (such as those present from infancy).
Retrograde amnesia involves the inability to retrieve information from before a trauma or brain injury. Individuals with retrograde amnesia may lose memories of past events, but they can often still form new memories.
Anterograde amnesia is characterized by the inability to form new memories after the onset of a trauma or injury, but past memories remain intact. This typically results from damage to areas such as the hippocampus, which plays a key role in memory formation.
Alzheimer’s disease is a progressive neurodegenerative disorder that primarily affects memory. Early stages involve difficulty forming new memories (similar to anterograde amnesia), while later stages can result in the loss of older memories and confusion about time and place.
Infantile Amnesia refers to the inability adults experience to remember personal events (episodic memory) from early childhood, typically before age 3 or 4. This is thought to be due to the underdevelopment of brain regions, like the hippocampus and the prefrontal cortex, which are essential for long-term memory storage.
