Which Expert?

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

Interaction Designer
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.
Source: Design

Information Architect (IA)
Description:
 The art and science of structure knowledge (technical data) and defining user interactions.
Source: Library Science

Usability Tester
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.
Source: Psychology

Accessibility
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?