Full Idea
The sense-datum theory is mainly to explain hallucinations and illusions, though there might be other theories, such as the 'adverbial' theory.
Gist of Idea
Sense-data (and the rival 'adverbial' theory) are to explain illusions and hallucinations
Source
Robert Audi (Epistemology: contemporary introduction [1998], I p.36)
Book Reference
Audi,Robert: 'Epistemology: a contemporary introduction' [Routledge 1998], p.36