Theoretical highlight 4: Memory

• Our memory is a necessary building block for our abilities to learn, think and act
• Information is perceived, processed and stored and then retrieved for use in cognitive processes and in actions

The memory is a necessary component of our cognitive system, not just for memorising information, but also for solving problems, and for interacting with computers. Some of the questions related to our memory structures and processes are: How do we take in the information? How is the information processed and then stored in memory? And how do we activate and retrieve the stored information when we want to use it in new operations? Other questions are how much information can the human cognitive system handle at one point in time? And how should the information be presented to facilitate processing? How should user training and support be designed to facilitate learning?

It is important to find the answers to all these questions - without memory we would not be able to process and make use of information input.

Our memory system consists of a number of systems that are relatively independent as regards duration and function.

• Sensory memory (SM)
• Short-term memory (STM)
• Long-term memory (LTM)

According to psychological theory, our memory consists of three relatively independent systems. They differ in function and duration. The sensory memory system (SM) is a very short memory. It has a duration of less than 0.3 seconds for icons, and 2 seconds for sounds, i.e. iconic information disappears from the sensory memory after 0.3 seconds and auditory information after 2 seconds. The information is passed on from the sensory memory to the short-term memory (STM). The information is actively processed in the short-term memory, and the duration of the STM is about 15 seconds that is not actively processed. Then information either disappears or is passed on to the long-term memory (LTM). Information that is stored in the long-term memory, can stay there "for ever".

• Not meaningful, "raw data"
• Limited speed in the categorisation and interpretation processes
• New input interferes with the information already stored in the sensory memory

All stimuli in our surrounding are stored, very briefly, before the attentional and interpretation processes start. One may think that the information stored in the sensory memory is like an after-effect, a remaining image, like the negative image you can "see" if you first look at a light bulb and then close your eyes. This is, however, not the case. Resent research has shown that the sensory memory is not an after-effect, it takes place "higher up" in the memory system. Psychological experiments have provided evidence that the information is processed to some extent in the sensory memory.

It is important to take the sensory memory and its limitations into account when designing user interfaces. Displaying too much information on the screen, in too short a time, makes it impossible for the user to categorise and interpret the information before it disappears and is replaced by other input in the sensory memory. This means that the information disappears before it can be passed on to the short-term memory where it can be processed and then, possibly, stored in the long-term memory.

• The categorised and interpreted information from the sensory memory is consciously perceived in the short-term memory
• The information is activated and processed. The short-term memory search is extremely rapid.
• The information disappears rapidly and cannot be retrieved unless it is stored in the long-term memory.

The short-term memory is not a simple storage where information is kept for a brief period of time. In the short-term memory, the information is processed on a conscious level. Searching in the short-term memory is extremely fast since all the information in the STM is activated and is immediately accessible. On the other hand, the information in the STM disappears very rapidly unless it is passed on and stored in the long-term memory. The information in the short-term memory comes from the sensory memory (initially from the surroundings) or from the long-term memory, i.e. information that has been stored previously and is now retrieved. The information is placed on the "worktable", i.e. the short-term memory, where it is activated and processed.

We pay a price for the accessibility and speed of the short-term memory in that it has very limited capacity. It can hold between 5 and 9 (alternatively 3-5) units of information activated at the same time. The short-term memory uses a chunking technique to overcome the limitations in capacity. It creates chunks of information out of smaller units of information. This means that the number of information units decreases, but the original units do not disappear. They are still activated and accessible as parts of larger units.

== Short-Term Memory Capacity
Illustration of how the short-term memory increases its capacity to hold information:

1. L E B P M O W A S T A I A F B
2. F I A T O P E L B M W S A A B
3. FIAT OPEL BMW SAAB

The example above illustrates the chunking process in the short-term memory. Lets presume that we set up an experiment where the test persons are shown line number 1 for a brief period of time, e.g. tenths of a second. If the test person is then asked to retrieve the letters, he/she will remember just a few. One way of making the memorising process more effective is to try to interpret the letters in some way. If the letters are presented as shown in line 2 they will acquire a meaning to the test person. The separate letters turn into four meaningful units as shown in line 3. Moreover, all four units can be related to one single unit of information, namely cars. This makes it much easier to memorise all the letters, despite the fact that the number of them exceeds the capacity of the short-term memory.

Some design principles to facilitate short-term memory processing.

• Different parts of an application must be related to one another to support the chunking process.
• Important information must be persistently presented or repeated or else it will be replaced by other input.
• Required information must be displayed on the screen in order for the user to keep it activated in the short-term memory.

As illustrated above, the chunking process in the short-term memory can be facilitated by "external" chunking and meaning making. For instance, by relating different parts of a computer system to one another, you make it easier for the user to combine them into meaningful chunks and to retain them in his/her short-term memory, or working memory. Important information that is displayed on the screen may have to be repeatedly displayed in order not to be supplanted by new information input. Information that is required in, for instance, a decision making process must be displayed on the screen pertaining to that decision so that the user can keep it activated throughout the process.

Long-Term Memory Contents

Some Design Principles for Facilitating the Function and Limitations of the Long-Term Memory

• A strong connection between semantic and episodic knowledge is necessary for effective learning and use.
• Skills should be documented and stored in, for instance, the system so that they can be activated when needed.

Long-term memory often stores information as separate units of episodic knowledge. This type of knowledge has no meaning unless it is connected to, organised into and integrated with a semantic network. Such a process will give meaning to the episodic knowledge, which facilitates the learning of that knowledge. The knowledge is also easier to retrieve if it is meaningful. It can then be used in, for instance, the interaction with an IT system to achieve optimal use of the system.

We also store different types of skills in the long-term memory, for instance, different ways of solving problems in the interaction with an IT system. The process of storing different skills can be supported in the design of the IT system. If, for instance, the different ways of solving interaction problems are documented and stored in the system, the user can retrieve that information when he/she runs into a similar problem. We know that it is very difficult for the user to retrieve information from memory about how to solve a particular problem unless that problem recurs frequently.

Recall. Look for, identify and activate the information - a minimum of clues. Recognition. Determine whether or not the presented information is the desired information - a maximum of clues.

The information in the long-term memory is stored, but not immediately accessible, unlike the information in the short-term memory. When we need information that is stored in the long-term memory we first have to locate it and retrieve it. There are different ways of searching for information in the long-term memory. Either by means of recall, i.e. to look for, identify and activate the information with little or no help of external clues. The other option is recognition, i.e. to compare information that is presented with the information that is stored in the memory and determine whether or not these pieces of information correspond. In the recognition condition we get a maximum of external clues from the presented information.

• Designs based on recall, e.g. commands, are more difficult to use and should be avoided. Recognition is better.
• Designs based on recognition, e.g. menus, are easier to use if the different options are easy to tell apart.
• Clues are more effective if the learning situation and environment resemble the real context of use.

Recall-based designs are much more difficult to use and should not be used in IT systems. It is much harder to look for and retrieve information when there are little or no clues present in the user interface, as in command-based interaction. Commands are difficult to remember, in particular those that are rarely used. Recognition is much easier since the information is actually presented, for instance as options on menus. With the information present on the screen it is much easier to remember what to do. Recognition can, moreover, be facilitated if the different options and menus are easy to tell apart, i.e. they differ in one or several respects. If they are too similar, it is difficult for the user to tell the one clue from the other and to compare the different options with the information stored in the long-term memory.

Clues are more effective when the situation and environment where we want to retrieve the information (i.e. the context of use) are similar or identical to the learning situation and environment. The reason is that each piece of information is coupled to a number of clues that were present in the situation where the information was stored. And we use those clues when we try to retrieve the information.

• Objections: the memory does not have to be divided into three different systems.
• The categorization and interpretation processes in the sensory memory are dependent on information activation in the long-term memory as well as in the short-term memory.
• Short-term memory processes the contents of the long-term memory, at least semantic knowledge.

The above description of the three different memory systems is based on the most powerful theory within memory research, but there are competing theories and models. There are research results that indicate that there may be just one memory system or two systems. One argument for a single memory system is the fact that the processes taking place in the sensory memory are highly dependent on information activation in both the long-term memory and the short-term memory. The processes cannot take place solely in the sensory memory, but use information and knowledge already stored in the long-term and short-term memory. Secondly, the short-term memory processes the contents of the long-term memory, at least in parts when connecting the activated information in the short-term memory to semantic networks in the long-term memory. This indicates that the memory does not have to be divided into three different systems.

The above provides a brief introduction to the structure and processes of our memory. In order to complete the picture you should read the literature and visit the links listed below.

Required Reading

• Benyon: Chap. 5.4, 15.1-15.7 (Dix: 1.3)