Class Notes for Chapter 7
Memory

The Three Stage Memory Theory

The Three Stage Memory Theory divides memory processing into the levels of sensory memory, short-term memory and long-term memory. Each of these levels is defined by its (1) function, (2) capacity and (3) duration.

 

Sensory Memory

Function: The primary function of sensory memory is to hold information just long enough for it to be selected for processing. Sensory memory also serves the adaptive function of helping us filter out large amounts of unimportant information taken in by our sense organs. Therefore, SM performs its function in a fraction of a second allowing us to selectively attend to important stimuli and disregard unimportant stimuli.

Duration: Information can be held in SM only for a brief time (a fraction of a second). Iconic SM (visual register) will hold an image of a stimulus for up to about 1/4 of a second. Echoic SM will hold a auditory image for up to about 3-4 seconds. If the image flashed into our SM is not tagged as relevant, attended to and moved into short-term memory, it will quickly be discarded.

Capacity: The capacity of SM is very limited. Depending on the amount of time exposure to the stimulus, SM can only hold a few bits of information at a time. Even though it is limited in its capacity, SM is said to hold an exact image of a stimulus. That is, the more cognitively active parts of our brains have not yet had the chance to alter the information as a part of the process of perceiving it.

 

Short-term Memory

Function: STM has two primary functions: (1) to hold information just long enough for it to be used and then discarded and (2) to hold information long enough to process it into long-term memory. Information held in STM that is not used or processed into LTM will be discarded. Example: (function #1) holding a telephone number long enough to dial it. Example: (function #2) holding a persons name while relating it to the persons face and storing the name in LTM.

Duration: STM will only hold information for up to about 30 seconds if the information is not rehearsed. That is, if the name of a person you've just met is heard, stored in STM briefly, but not processed into LTM or rehearsed, it will likely be forgotten after about 20 - 30 seconds. Therefore it is important to note that STM is rehearsal dependent. In order to hold information in STM for longer than 20 - 30 seconds, it must be rehearsed. If something interrupts the rehearsal process, the information will likely be forgotten (if it has not already made its way into LTM). As Benjamin Lahey notes, keeping several bits of information in STM is like juggling several eggs. As long as you pay attention and are not distracted from your juggling, you can continue the task. If you are distracted from the task, the results will not be good.

Capacity: STM can only hold about 7 bits (+/-2 bits) of information at a time. That is, the average is 7 (+/-2) with a common range of 5 - 9 bits. A bit of information might be a number, letter, name or object. One way we can organize and arrange information in order to store more in STM is through the process of chunking. For example the number 2148815715 can become (214) 881-5715, which is much more manageable for our STM.

 

Long-term Memory

Function: The obvious function of LTM is to hold information for an extended period of time that we need to be able to function adaptively in our daily lives. With out LTM, we would not be able to remember aspects of our identity, how to live safely or how to do any simple task of living. Three of the primary function types of LTM include:

Semantic Memory -- the ability to recall meanings of concepts.
 Procedural Memory -- the ability to recall the correct order of steps needed to        successfully complete a task.
 Episodic Memory -- the ability to recall the sequence of happenings in an witnessed event.

Duration: According to most memory theorists, the memories we process into our LTMs are relatively permanent. That is, most theorists believe once information is processed into LTM that it is, in some form, always there. Some question this asking, "then why do I forget things?" Memory theorists reply that the trouble is most often in the retrieval process. One of the two primary retrieval processes is much easier to use as noted below. Retrieval processes include:

Recall -- retrieving information on the basis of a simple cue ("What is your home address?).
 Recognition -- retrieving information by selecting from several choices provided ("I can't remember the name of the breakfast cereal my wife asked me to buy so I'll go to the cereal isle and look at all of the boxes. Then I'll recognize the right one when I see it.").

Capacity: The capacity of LTM is believed to be unlimited. We can store an entire life-time of memories, knowledge and experiences in a brain that, if anything, gets slightly smaller (not larger) as we move into later adulthood. Getting information into LTM may be difficult if one of the following processes is not used:

Experience & Meaning -- first and foremost, LTM store information on the basis of meaning. Personally relevant life experiences, especially emotionally powerful experiences, are processed deeply into our LTMs.

Categorization -- LTM also stores information on the basis of categories, classes, and relationships

Novelty -- information that is distinctive, unusual or unique is also easily processed into LTM.

Repetition and Rehearsal -- not the most effective method of LTM processing, repetition can be used to process information into LTM, especially if the information is meaningless, not easily categorized, or not novel.