Constraint is a method of limiting the actions that can perform on a design. For example, should not insert coins in a card slot. There are 2 types of constraint :
  1. Physical constraint
  2. Psychological constraint

Physical Constraint

  • Limiting the range of possible actions by redirecting physical motion in specific ways.
  • It is useful for reducing the sensitivity of controls to unwanted inputs.
  • Path : Applied forces into linear motion. For example, scroll bars. It is useful where the control variable range is small and bounded.
  • Axes : Applied forces into rotary motion. Example, trackball. It is useful where the control real estate is limited, larger or not bounded.

Figure 6.2.1:electrical fan regulator
For example, electrical fan regulator is used to control the speed and the spinning of the fan.
  • Barriers : Applied halting, slowing or redirecting forces around the barriers. Also, useful for denying errant or undesired actions.
Figure 6.2.2:road sign

For example, the road sign that purposely colour in red is used as a barrier to get the drivers' attention and be more careful on the road especially when on conjunction.

Psychological Constraints

  • Limiting the range of possible actions by leveraging the way people perceive and think about the world.
  • Symbols : Influence behavior by communicating meaning through language such as icon and signage.

Figure 6.2.3:road sign
 For example, the road sign is purposely colour in red because since kid, human had been teach that red colour is a warning sign and it may comes with meaning of dangerous. So whenever people saw this warning sign they will stop.
  • Conventions:Influence behavior based on learned traditions and practice such as traffic light.

Figure 6.2.4:woman bathroom sign

 For example, since kid we know that girl or woman is wearing skirt as symbolic for feminine style. Therefore whenever go to toilet especially a girl just by looking the symbol people know it is for woman not for a man.
    • Mappings: Influence behavior based on the perceived relationship between elements.

    Figure 6.2.5:danger sign warning

    For example, the word of danger is using lightning struck mapping because most people scared of lightning. The designer design this kind of mapping is to make people to avoid the place and at the same time can secure their life.

    Figure 6.2.6:direction signboard
    For example, the designer used this kind of mapping to tell people that the way to their destination is on the right. Whenever people saw this mapping automatically their body will turn to the right not left.

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