Can a defendant be found mentally incompetent to stand trial?

A person cannot be tried or adjudged to punishment while mentally incompetent. (Pen. Code, 1367, subd. (a).) A person is mentally incompetent if, as a result of a mental disorder or developmental disability, he is unable to understand the nature of the criminal proceedings or to assist counsel in the conduct of a defense in a rational manner. (Ibid.) When the defendant presents substantial evidence of incompetence, due process requires that the trial court conduct a full competency hearing. (People v. Koontz (2002) 27 Cal.4th 1041, 1063.) Evidence is substantial if it raises a reasonable doubt about the defendant's competence. (Id. at p. 1064.)