Memory — An Overview
Your memory allows you to retrieve a memory. While this may sound simple enough, memory is actually a very tricky and complex thing. Let's first take a look at the basics of how memory works.
Think of memory as a huge, selective storage system that is capable of storing an immeasurable amount of information. Memory is reliant upon three components: encoding, storage, and retrieval. Encoding refers to the intake of information and the brain's conversion of that information into a form it is able to process. Storage refers to the placement of this processed information in the brain. The information may be stored as an image, a concept, or within a mental network. Retrieval, of course, refers to the recovery of that information and putting that information to use.
Filling in the Gaps
Most people would like to think (and may even insist) that they are able to retrieve certain memories with every shining detail in place. For instance, you may swear you remember perfectly well the moment your husband proposed to you, including all details — after all, that was such a special occasion, how could you possibly forget? However, if you were asked to recall the event in detail, you would likely misremember several details and may even make up some others! This is because the retrieval of memories is a reconstructive process in which you retrieve certain flashes of the event but fill in the gaps for those details that the memory didn't store or process properly.
The memory is selective. It will not store every single event that happens to you or every little detail or bit of information you take in. It has to be selective in order to keep the house clean, so to speak. If it were not, your mind would be cluttered with tons of insignificant and useless information.
Because you are forced to reconstruct the past somewhat when recalling a memory, you often rely on several other sources to fill in the gaps, often without even knowing that you are doing it — which explains why you might insist that you are recalling your memories perfectly. For instance, you may draw conclusions from photos or video of the event in question; stories others have told about the event; anything you may have said, thought, or felt about the event after the fact; or sometimes even wishful thinking (what you wanted the memory to be).
Implicit and Explicit Memory
As you well know, there are some things you work really hard to remember, such as information for an upcoming exam, and other things that you really have no desire to remember, but remember anyway, such as commercial jingles. So what's the difference?
The retrieval of explicit memory is usually tested in one of two ways: recall or recognition. Recall refers to the ability to actually retrieve that information you stored, such as in fill-in-the-blank or essay questions. Recognition refers to the ability to recognize the information stored, such as in multiple choice or true/false questions.
The information that you intentionally work to remember is stored using explicit memory. Because you have spent energy to deliberately remember this information, it makes sense that the memory would store it. The information that you remember but did not intentionally put away for future use is stored using implicit memory. While it seems that this type of information must have affected you in some way, it is not certain exactly why this information is stored in memory.