The Memory Storage Systems: Memory Storehouses

i.  Sensory Memory
ii.  Short - term Memory
iii.  Long - term Memory 

•  These three are not separate, mutually exclusive, entities found in separate brain centers;
•  They differ in terms of the functions they perform and their capacity for retaining information for a specific period of time i.e., for how long can they keep the information stored.
•  These are abstract divisions on the basis of their primary characteristics.

Sensory Memory

 
•  Storage of memory lasting for a while; this is the initial momentary stage.
•  Sensory memory refers to the initial, momentary recording of information in our sensory systems.
 

When sensations strike our eyes, they linger briefly inthe visual system. This kind of sensory memory is called iconic memory and refers to the usually brief visual persistence of information as it is being interpreted by the visual system. Echoic memory isthe name applied to the same phenomenon in the auditory domain: the brief mental echo that persists after information has been heard. Similar systems are assumed to exist for other sensory systems (touch, taste, and smell). However researchers have studied these senses less thoroughly. 

American psychologist George Sperling demonstrated the existence of sensory memory in an experiment in 1960.

•  The person’s sensory system records information as a raw and non-meaningful stimulus: e.g., a fly that sat on your nose in the park this morning, the sound of the car that passed by you, or the feel of the dry leaf that landed on your head when you were waiting for the bus.

•  Sensory memory systems typically function outside of awareness and store information for only a very short time. Iconic memory seems to last less than a second. Echoic memory probably lasts a bit longer; estimates range up to three or four seconds. Usually the incoming sensory information replaces the old information. For example, when wemove our eyes, new visual input masks or erases the first image. The information in sensory memory vanishes unless it captures our attention and enters the working memory.

Types of Sensory Memories

i.  Iconic Memory
ii.  Echoic Memory
iii.  Memories related to other senses
 

Iconic Memory
The information gathered by our visual sense is reflected by the iconic memory; memory in the visual domain
 

Echoic Memory
The information coming from our auditory sense is dealt with by the echoic memory; i.e., Memory for sounds:
•  Sensory memory is short lived. Ranging from just about one second to a few seconds, its duration depends upon the intensity of the stimulus too.
•  Iconic memory may fade in less than a second, whereas the echoic memory may last for 3-4 seconds.
•  The stimuli that have a high intensity may stay for a bit longer
•  Sensory memory is like a temporary image that may vanish forever, and may be replaced by another if it is not shifted to another processing system or memory storehouse

The representation of the world around us captured by sensory memory is relatively complete, full and detailed.

Short-term Memory/ Working Memory

•  Psychologists originally used the term short-term memoryto refer to the ability to hold information in mind over a brief period of time. As conceptions of short-term memory expanded to include more than just the brief storage of information, psychologists created new terminology. The term working memoryis now commonly used to refer to a broader system that both stores information briefly and allows manipulation and use of the stored information.
•  This system is higher in functioning than sensory memory, as it stores information in terms of meaning and not just simple sensory stimulation.
•  Sensory information is meaningless and therefore discarded.
•  If it is sent to the short- term memory then a meaning is added to it.
•  Since now it is meaningful it will be retained, though for not very long.
•  Short-term memory retains information for 15 to 25 seconds, unless it is moved into the long- term memory.
How is sensory memory transformed into short-term memory?
o  The exact process is not yet clearly known
o  There are two main theories in this regard: 

a)  The transformation takes place when the sensory stimulus is converted into words
b)  The transformation takes place after the sensory information is converted into graphic representations or images.
 

Chunking and the capacity of Short-term memory
•  The information stored in short-term memory is in the form of a single unit, comprising several chunks.

•  A chunk is an understandable or meaningful set or grouping of stimuli e.g., “001023” can be learnt as “0 0 1 0 2 3” OR “00 10 23”.
•  Short-term memory can carry seven chunks at a time on average; the capacity may be two more or two less than seven (George Miller).