You may come across some of the following terminology and concepts in your reading on memory loss. Here is a brief explanation of some of the most common terms used. The brain is an incredibly complex machine and there are several different ‘models’ used by doctors, scientists and psychologists to try to categorise and define the different types of memory humans have so this list is by no means definitive and you may also find some variations on the subdivisions.
- Immediate memory or sensory memory – this lasts less than a second and is the memory of what you absorb going on around you at any given time. If you remembered every single thing that you saw, felt, smelled, heard and tasted through the day you would be overwhelmed so your brain just filters fleeting impressions which may or may not become short term memory, depending on their relevance. Sensory memory can also be divided into;
- Iconic memory – fast decaying visual memory
- Echoic memory – fast decaying auditory memory
- Haptic memory – fast decaying tactile memory
- Short term memory or working memory. This type of memory lasts for more than a minute and is the ‘what did you have for breakfast?’ memory. It starts to decay after half an hour unless something happens to reinforce it. This part of our memories is believed to only have a capacity of 5-7 things at any given time but by using a technique called ‘chunking’ we can expand on this capacity. The best known example of this was when the Bell telephone company decided to divide telephone numbers into groups of 3-4 digits. It is much easier for us to remember these small groups of numbers as each group of numbers becomes one thing. At the same time by rehearsing these chunks of numbers we are then committing them to long term memory.
- Long term memory. This is the memory that in theory lasts a lifetime and has an infinite capacity. Unless we make an active effort, however, to recall and reinforce these memories they too will ultimately start to fade. This is why the things we learn at school tend to be forgotten once the exams are written and the information is no longer relevant, unless we continue to read and study in those same fields and make an active effort to reinforce those neural pathways.
Long term memory is in itself divided into further categories:
- Explicit or conscious memory which can be subdivided into episodic memory – our ability to remember events and experiences and semantic memory which is our ability to remember facts or concepts. An example of episodic memory would be remembering your child’s christening or other events in your own life. An example of semantic memory would be remembering important dates from history at school.
- Implicit or unconscious memory. Also called procedural memory, this is the memory that holds skills and tasks and explains why someone with Alzheimer’s disease may still be able to ride a bicycle or sing a song long after they have lost their verbal skills.
- Prospective memory. This is our ability to remember things that we have to do, our mental ‘to do list’. Once again, this part of our memory has a limited capacity for possibly 10 things at any given time which is why busy people find they need to keep diaries and lists to make sure that they don’t overlook an appointment or forget to pick up the dry cleaning. Once again, this memory can be boosted through various management plans. For example by creating routines so that something becomes a habit. Getting up at 6 a.m. to catch the bus to work at 7 a.m. is something that you can do without thinking about it if you do it every day and it becomes intuitive. Then your prospective memory only has to focus on the unusual items that are the exception to the rule, such as going to the dentist at 10.30 on Friday morning.