What type of document allows individuals to specify their preferences for medical treatment if they become incapacitated?

The correct choice is a document known as an advance directive. This legal instrument enables individuals to articulate their healthcare preferences in advance, particularly regarding medical treatment in situations where they may become incapacitated and unable to communicate their wishes. Advance directives serve as a vital tool to ensure that individuals receive care that aligns with their values and preferences during critical medical circumstances.

Advance directives encompass various forms, including living wills and medical power of attorney documents. A living will specifically outlines the types of medical interventions one may or may not wish to receive, whereas the power of attorney designates an individual to make healthcare decisions on behalf of another person if they are unable to do so.

In contrast, a health care proxy is a type of advance directive that appoints someone to make medical decisions on an individual's behalf. However, the term "advance directive" is a broader category that includes both living wills and health care proxies, thereby making it the most comprehensive term among the choices presented.