Perception can be defined as the cognitive processes that give coherence and meaning to input we receive through our senses. When it comes to visual perception we are susceptible to illusions.

Constructivist Approach

Gregory takes the constructivist approach which describes our perception as being a process of construction. We construct a world from information in the environment and our own knowledge. This image of the world is therefore not what the actual world looks like, rather it is the result of our brain processing the information received as visual input.

"the visual world constructs a model of the world by transforming, enhancing, distorting and discarding information" (Gregory, 1978)

Ecological Approach

Affordances

Affordances relate to how we perceive the behaviour of systems or objects. If a door "affords" opening, for example, it is obvious to us that it should be opened. If an object has a clear affordance, we know what to do with it.

It is important to note that metaphors, such as those you see on your computer screen (the "trash can" for deleting files, "buttons" for clicking etc...), are not affordances. We simply translate the affordances associated with the real life equivalents into the computer world so that we can guess what these things on our computer screens do!

Applying Perception to ISD and HCI

There are various graphical modelling techniques that can be used to represent information in an interface. If graphical objects are created so that their meaning can be perceived correctly in a successful manner, this will lead to better systems design.

There are many different techniques used to affect our perception of items represented on a computer screen. 3D representation can be achieved by using depth cues to create a feeling or perception of depth. Size, texture, shadow, contrast, and brightness are all factors that can be changed to alter our perception.

Mappings

Mappings can be arbitrary or direct. Direct mappings bear a correspondence between objects represented and the form of representation used. For example, a file which is large in size may appear as a larger icon within a system environment. An arbitrary mapping would be colour coding file sizes so that blue meant large, green meant medium sized, and black mean small. These mappings have no significant meaning to us unless they learnt.

This is where direct mappings come in useful as they mean that less learning is normally involved. This is beneficial for users who are inexperienced.

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