Careful usability design is an essential part of the overall design process of the objects if you want your product to reach its full potential, therefore it is essential to take into account all the usability principles, so the product can adapt to the skills of the users.
Good design of usability aspects is a critical requirement for product reliability in some cases, many of the user errors are caused by the fact that at the design stage the real capabilities of users in their environment have not been taken into account.
Not considering the usability aspects often means preventing the user from accessing certain features of the product, causing him to make mistakes and, therefore, considering the product as something useless rather than an aid.
When making design decisions that affect the user, one should consider the physical and mental capabilities of the people who will use the product.
People have a limited short-term memory, they can instantly remember about seven objects, so if you present too much information to users at the same time they might not be able to assimilate and / or manage them all.
Everybody makes mistakes, especially when too much information have to be deal with or when users are under stress; when systems fails and sends notifications or triggers alarms, it causes further stress for users, increasing the chances that they will make further mistakes.
Everyone has different physical abilities, some people see and feel better than others, someother are colorblind, some are very good with manual work etc etc. This is to demonstrate that you should never design according to your skills and assume that all users understands how to use it.
These human factors underlie the design principles listed below:
- User familiarity: the product should take into account the experience of the people who will make the most use of it.
- Consistency: the functionality design should be consistent so that when possible the functions are activated in similar ways, perhaps in the manner of other similar products.
- Minimal surprises: the user should never be surprised about the behavior of the product.
- Recoverability: the product should include mechanisms that allow users to restore the status in the event of an error.
- User Guide: The product should provide significant feedback to the user when errors occur and provide help features depending on the context.
- Diversity of users: the product should provide interaction functionalities suitable for the different types of users of the system
The term was introduced in 1979 by the American psychologist James Gibson in the work An ecological approach to visual perception.
Each object has its affordances, as well as the surfaces, the events and the places, the higher the affordance, the more automatic and intuitive the use of a device or an instrument will be.
For example, the appearance of a handle should make the best sense and automatically how the door should be opened: if pulled, pushed, or slid (a door that opens automatically to the passage has a poor affordance, since it is very unintuitive how it works).
Thus, with affordance, an important design parameter is defined: the physical quality of an object that suggests to a user the appropriate actions to use it.
Among the objects with an excellent affordance there are, for example, the fork or the spoon, tools that have been improved over the millennia up to the extremely intuitive and very simple use of today.
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