There are so many fields of UX Design that it becomes very difficult to decide which expert to choose. Well, we are going to advise you on which expert is more suitable for which job.
The User Experience Designer
Description: Generally refering to someone that focuses on the user experience relating to technology interactions, primarily with mobile device software, desktop software, and websites and website applications.
Source: Psychology, Information Architect, Design
Description: A person that examines behaviours in physical and virtual spaces and the convergence of physical and virtual products. He/she focuses on designing behaviour between two entities, which are not limited to human and computer pairs; the focus is on designing a set of tasks.
Information Architect (IA)
Description: The art and science of structure knowledge (technical data) and defining user interactions.
Source: Library Science
Description: Testing the ease of use of a tool or human-made object in relation to achieving certain specified goals with effectiveness, efficiency and satisfaction.
Description: How easy it is for people to get to, use, and understand things.
Source: WAI, Disabilities Rights Movement
Human-Computer Interaction (HCI)
Description: The Study of interaction between people and computers.
Source: Computer Science
Human Factors Engineering (Ergonomics)
Description: Optimising the interface between human beings, the designed objects and the enviroment they interact with.
Source: Health Sciences
User Interface Designer
Description: Designing interaction between human and computers by applying graphic design, information design and usability.
Source: Design, Engineering
What they all have in common is to facilitate an intuitive workflow.
Description Source: What is User Experience Design?