Constaint

Physical Constraint

Example: Child Lock

Photo source: Myvi Car

Figure 6.1.1 shows child lock in cars

Physical constraints limit physical actions by reducing and specifying physical motions. 
The child lock function as seen in Figure 6.1.1 displays an example of barrier (physical constraint) in design. When activated, the function stops a child from opening the car door until an adult opens it from the outside. Therefore, the barrier acts as a physical constraint by preventing a child from opening the door from inside.

Psychological Constraint

Example: Sims 3 Game Interface 

Picture Source: Print screen from Sims 3 Interface

Psychological constraint limits possible action through the way people think.
Physiological constraints can be further divided into symbols, conventions, and mappings.

• Symbols

Figure 6.1.2 shows the usage of symbols in Sims 3 (highlighted in orange) 

     Symbols communicates with the user through perceivable cues such as text, icons and sounds.

     In the Sims 3 game interface, symbols as highlighted in Figure 6.1.2 are seen in the build-a-house mode, whereby icons in the form of commonly-encountered home furniture are used to symbolizes different parts of the house. For example, if the player wants to buy furniture to build a bathroom, the player will automatically click on the icon of the toilet bowl, or click on the icon of the sofa if the player intends to buy furniture for the living room. Therefore the toilet bowl and sofa icon serve as perceivable cues to communicate with the player. 

• Conventions

Figure 6.1.3 shows the needs bars of a Sim in Sims 3, whereby red shows low and green indicates high and satisfied need.

     Conventions influences behaviour through our existing knowledge which are gained through practices and learned behaviours. 

     For example, the colour indicator of the needs bars seen in Figure 6.1.3 utilizes colour conventions, whereby a red bar indicates that the particular need is low and have to be fulfilled (as most people associate red with danger and warning) whereas the green bar indicates that the particular need is high and satisfied (most people associate green with something pleasant and lively)

• Mappings

Figure 6.1.4 shows the usage of mapping to control the screen of the game (highlighted in orange)

     Mappings constraints behaviour based on the perceived relationship between the features. 

     For example, the screen controller as highlighted in Figure 6.1.4 maps the relationship between the controls and their movements or effect after being clicked. For example. mapping exists when the player understands that clicking the '+' sign will zoom in the screen whereas the '-' sign is for zooming out from the screen. Hence the player is able to map the relationship between the screen controller buttons and their relative effect, which is either to zoom in or out.