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What is spatial memory? Memory is a given, but what does spatial refer to? According to the Concise English Dictionary, the definition is as follows:
"Spatial or spacial adj relating to or occurring in space."
Spatial memory, therefore, relates to how the brain stores information regarding the location of physical objects in space - the environment around you. Spatial memory is extremely vital for many species' survival, including us humans: it allows you to find your way in a familiar city, it allows a rat to learn the location of food in a maze, and it allows cats to find their food bowl in the kitchen. Obviously, earlier on in our evolution, it allowed our ancestors to locate sources of water, food, and shelter.
On a side note, research (Kessels, 2002) has shown that spatial memory is not specifically tied to the right hemisphere of the brain (the left hemisphere for some left-handed people), as was thought (and proclaimed in popular psychology). The theory now is that spatial memory consists of a set of sub processes (and of course, as is usually the case in psychology, spatial memory itself is a sub-process), some of which take place in the left hemisphere, and some in the right hemisphere. Just in case you want to know.
A good, real-world example of spatial memory is the tea box I have in my kitchen. It is a wooden box with a lid, and the inside of the box is divided into 12 squares, each of which carries a specific tea - Earl Grey, traditional English tea, Ceylon, mango, cinnamon, you name it. My tea box is located in one of the top kitchen cabinets, and seeing I am not a very tall guy, I cannot look into the box without taking it out of the cabinet. Now, over time, spatial memory has allowed me to learn in which square each of the individual types of tea are. Without specifically sitting down, with the box in front of me, learning each tea's location, spatial memory has gradually taught me where each type is. I do not have to take the box out if I want cinnamon tea - I know, by spatial memory, which square I need to put my fingers into.
Now, how does spatial memory apply to the world of graphical user interfaces? Take the application menubar for example. Just look at a set of screenshots of various menubars in Windows XP (Media Center Edition 2005, in case you want to know):
As you can see, and, as you probably already know, menubars in one operating system (and, in fact, even across various operating systems) are fairly consistent, at least for the first three to four entries. Whenever an application breaks the usual menu arrangements, like one of the examples above (that is Notepad++, in case you want to know), it stands out, simply because it does not follow the usual pattern. If we go one level deeper, into the individual menus, you will notice that even those tend to be arranged in a consistent manner (where possible, of course).
Spatial memory is one of the prime reasons why a consistent user interface goes a long way in making an interface easy to use. If a user is confronted with a new graphical user interface for the first time, it really helps if applications follow a consistent menubar layout, menu layout, and so on. The user will not be forced to learn specific layouts for each individual application; after having used applications A, B, and C, the brain will get around in menus in application D much faster if they follow the same layout as A, B, and C. That may seem like elementary knowledge, but I still see a lot of people calling consistency freaks like me whiners. When a user complains of an inconsistent user interface - they are definitely not whining.
There is one fairly obvious side note to the importance of spatial memory in relation to graphical user interfaces: isn't it the case that spatial memory in humans is tailored for a 3D environment? This becomes even more the case as soon as you realise that our ancestors were moving up and down trees, putting additional importance on the third dimension. In other words, how useful is the human spatial memory in today's 2D interfaces?
An interesting study performed in New Zealand gives some very, very interesting insights into this particular question (Cockburn & McKenzie, 2002). Cockburn & McKenzie set up various virtual, as well as real world interfaces, which varied the ability of test subjects to use the 3rd dimension. "The aim of the experiment is to investigate differences in people's ability to use their spatial memory in physical and virtual systems, and to see what effects occur as richer levels of a third dimension are available."
The results were, to me, unexpected. "Results show that the subjects' performance deteriorated in both the physical and virtual systems as their freedom to locate items in the third dimension increased. Subjective measures reinforce the performance measures, indicating that users found interfaces with higher dimensions more 'cluttered' and less efficient." In other words, the test subjects' difficulty with spatial memory related tasks increased as the interfaces went from 2D, to "2.5D", to 3D - not only did their reaction times increase, their assessment of the task was more negative as well.
In other words, users do, in fact, benefit from spatial memory for 2D tasks, despite the fact that you would think that the human spatial memory system would be tailored to 3D tasks. This is probably also one of the prime reasons why there seems to be little incentive in the computing world by companies like Microsoft and Apple to move to true 3D interfaces - I am sure their usability testing came up with similar results as the New Zealand study.
How important would I rate spatial memory when it comes to usability and graphical user interfaces? Considering that it is a building block (or a sub-process if you will) of not only learning in general, but also specifically of learning the locations of items (both physical as well as virtual), I would rate it as a very important aspect, something user interface designers should really take into account. Seeing graphical user interfaces are all about allowing the user to access [find] functionality [objects] in an interface [space], spatial memory is a vital cognitive element.
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