It is generally accepted that human memory is divided into three fundamental stages : Sensory Memory, Short Term Memory and Long Term Memory. Each memory stage works and functions in a different way but all three work sequentially together.
This is extremely short term memory possibly as briefly as just a quarter of a second. We use this to process the huge amount of information arriving to our brain via our senses. Iconic Memory is the name given to the fleeting visual images that we see. Echoic Memory represents the sounds that we hear and Haptic Memory represents touch.
If you consider the vast amount of sensory information arriving via our senses, you can consider Sensory Memory as perhaps a filter. We have no control over what information is stored in Sensory Memory but can choose which parts to extract and move to Short Term Memory.
Most people are familiar with the term short term memory but there's two things that people don't usually know. First is that the length of time we store things in our short term memory is actually very short. In fact, short term memory storage is less than a minute. Secondly, the amount of information we can store in short term memory is very small. Some scientists now think it's as little as 4-6 items.
The purpose of short term memory is generally to help hold things together until you can store in longer term memory. For example, if you are reading a sentence, then it's useful to be able to remember the beginning until you have got to the end. Then, you can 'digest' the content and decide whether to store it to long term memory or not.
The more modern concept of working memory tends to also view this stage as a temporary holding place for information as well. For example, the ability to recall and write down a telephone number which you then promptly 'forget' because it wasn't stored to long term memory.
This is the big one. This is the 'hard drive' where you store all your memories after they have moved from Short Term memory. Unlike Sensory or Short Term memory, Long Term memory can hold information for potentially a life time and the size and depth cannot be measured.
That's not to say that you can remember everything of course. In fact, longer term memories tend to be stored with different strengths and your ability to recall different memories isn't the same. Additionally, long term memory can fade and regular recall of these memories is required to preserve them for longer.
If you have taken the test, you will have realised that the Memory Test can take several minutes. Which means that the procedure is testing your long term memory rather than your short term memory. In fact, it's testing two fundamental elements. Firstly, the ability for you to pass the information you are seeing into long term memory and the subsequent recall. Secondly, it's testing your ability to concentrate and not be distracted during the consolidation or storage stage. One of the reasons we place adverts on the storage section is that the adverts are likely to distract you. In doing so, your ability to successfully transfer from short term to long term can be disrupted.