Short-Term Memory and Working Memory
When an impression makes it through the sensory memory and then moves on to the short-term memory, it is processed, or encoded, and is turned into a pattern the brain can recognize, such as a word. The information does not stay long in the short-term memory either, only about twenty seconds.
The short-term memory deals with only the present time. It stores everything you are conscious of at the moment: the words you are reading, the food you are eating, the sound of a dog barking outside, the telephone number you just looked up, etc. The brain then decides whether to move this information on to the long-term memory or discard it.
The short-term memory can hold only so much information at any given time. But just how many items can it store? For several years, the magic number was seven, give or take two. This gives a good explanation for the number of digits in zip codes (five digits), phone numbers (seven digits), and social security numbers (nine digits). However, not everyone agrees with this number. Some have placed the number of items to be as few as two, while others place the number of items as high as twenty. Regardless, the short-term memory isn't able to hold very many items at one time.
The short-term memory can be a source of frustration for many people. Depending on how quickly you are receiving new information to replace the information already there, items may be displaced before you are ready to part with them. However, after you look up a phone number, mentally rehearsing it allows you to keep it in short-term memory until you are able to pick up the phone and dial the number.
Luckily, you are able to combine bits of information into large chunks of information, where each chunk counts as one item. Thus you are able to store more information than you think. For instance, most people store the term DVD as one item, or chunk, rather than as three separate words (items). Along the same lines, you will often see businesses with phone numbers that can be stored as one chunk, such as 555-PETS, instead of seven individual items.
The Working Memory
The short-term memory not only stores new incoming information, but it can also hold information that has been retrieved from the long-term memory to be used temporarily. The system within the short-term memory that processes and interprets the incoming information from the long-term memory is referred to as the working memory. For instance, if you are thinking of purchasing a sale item with a particular percentage discounted, your working memory handles the numbers you are working with as well as the instructions brought forth from the long-term memory for completing the mathematical equation to find out the price of the item.