Few problems fall solely into one design discipline’s skillset. The lines between them are blurry. For example, even a basic user interface problem has elements of communication design and experience design. Most designers are comfortable in more than just one area. Just like medical doctors, designers tend to go through some common training (like visual thinking for example), then they hone their skills further and specialize in certain areas over others.
Since you have selected Objects & Artifacts, then here is some further information on the design skillsets that may be needed in this category.
Industrial design or Product design most often focuses on a combination of aesthetics and user-focused considerations to provide tangible object-based solutions for problems of form, function, physical ergonomics, and sustainability. It is also considered as the creative act of determining and defining a product's form and features in advance of the physical act of making a product, which consists purely of repeated, often automated, replication.
User Interface (UI) or User Interaction design is about user interfaces for machines and software, such as computers, home appliances, mobile devices, and other electronic devices, with the focus on maximizing usability and the user experience. The goal of user interface design is to make the user’s interaction as simple and efficient as possible, in terms of accomplishing user goals.