Cognitive Psychology: Human Memory

By: Dr. Susan Siegfried, Clinical Psychology

Memory is the ability to retain information over time through three processes: encoding, storing and retrieving. Memories are not copies but representations of the world that vary in accuracy and are subject to error and bias. There are three types of memory: sensory memory, short-term memory and long-term memory.

Sensory Memory

Iconic Memory is a form of sensory memory that automatically holds visual information for about a quarter of a second or more. As soon as you shift your attention, the information disappears.

Iconic means image. That is a quick image. Your eyes blink about 14,000 times in a day. But the world does not disappear when you blink. You do not have a split second of blindness because your eyes are closed. It is iconic memory that facilitates this failure to lose vision when blinking.

Echoic Memory is a form of sensory memory that holds auditory information for one or two seconds. Let us say you are reading a book or watching TV and you are completely engrossed in the story.  Your friend asks you a question and you stop reading and say “What did you say?” Just as those words come out of your mouth you realize that you can remember or play back your friends question. That is because it is still in your echoic memory.  It can last as long as two seconds. Besides letting you play back things you thought you did not ear, echoic memory lets you hold speech sounds long enough to know that sequences of certain sounds form words.

Short-term Memory

Short term memory saves information for a short period of time. It has limited capacity so things have to be removed to make room for more. Short term memory is also called working memory. Brain scans show that short term memory involves the prefrontal area of the brain. The act of paying attention transfers information into short term memory. After a short period of time information disappears unless it is rehearsed. Some information is eventually transferred from short term memory into long term memory.  More information is lost than is transferred. Memory structures vary in their level of activation, which determines how rapidly and successfully we can access the memories.  Unless attended, a memory structure’s activation level will decay away in a matter of seconds. To be activated again, the memory structure needs to be reactivated. We can maintain things in an active state by rehearsing them. The number of things one can keep active is determined by the rate at which we can rehearse them. Memory structures also vary in terms of their long-term strength determines our long-term retention of a memory.

Long-term Memory

Long Term memory is the process of storing almost unlimited amounts of information over long periods of time with the ability to retrieve it, remembering, for future use. How accurately you can retrieve it depends and many factors. To be recalled from long-term memory, information must be activated. Activation spreads along paths through a long term network of associations from the currently active portion of memory to the to-be-retrieved portion. The level of activation spread to a knowledge structure depends directly on the strength of the path along which the activation spreads ad inversely on the number of competing paths. The detrimental effect of competing paths on the amount of activation spread down a path is referred to as associative interference. The strength of knowledge structure increases with practice of the structure, but there is diminishing benefits from practice. The form of this practice effect conforms to a power function.

Long-term Memory: Declarative and Procedural

There are two types of long term memory, Declarative and procedural.  Declarative memory involves memories for facts and events, stories, words, conversations, facts, or daily events. We are aware of these memories and we can recall or retrieve these memories usually in language. Semantic memory is a type of declarative memory that involves knowledge of facts, concepts, words, definitions and language rules. Episodic memory is a type of declarative memory and involves knowledge of specific events, personal experiences or activities such as naming or describing.

Procedural memory involves memories of motor skills, some cognitive skills such as learning to read and emotional behaviors learned through classical conditioning.  These are often thought of as phobias although not always extreme enough to diagnose. We cannot retrieve or recall procedural memories verbally.

Retrieving Memories

Retrieving is the process of selecting information from long-term memory and transferring it back into short-term memory. There are several reasons why you cannot remember. It may not have been efficiently encoded if you were distracted and lost attention. The key to long term storage of information is effectively encoding information which required paying attention.  The most common way this is done is by making association between the old stored memories and the new. If the level of activation of a knowledge structure is low, because of either low strength or associative interference be will be a failure of recall. The strength of knowledge structure decreases with the retention interval, but the rate of decrease slows down with time. The form of this forgetting process conforms to a power function.

Interference from other information associated with a concept can slow down the speed at which the fact can be retrieved. Memories also seem to decay systematically. Interference is not the only reason for forgetting. Memories also seem to decay very systematically with delay, independent of interference.

Accuracy of long term memory is an interesting topic. Researchers have found that long term memories may undergo change and distortion across time and not always be as accurate as people may think. Long term memories are bias in that you are matching them to a preconceived idea also they are colored by the emotion of the moment which alters the memory.

Finally, we must ask, “Are forgotten memories truly lost?”  It is possible that we never do really lose our memories. Forgotten memories are still there but too weak to be revived. Researchers have electrically stimulated portions of the brain (temporal lobes) to find that people remembered what they thought were lost. Memories are the essence of who we are. They are precious and it is amazing they are as strong as they are when we look at the complicated process involved in storing them.


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