Mental Disease: A Bar to Proceeding or Sentence

A person can neither be proceeded against nor sentenced after conviction while he is incompetent as defined in this Section:

(a)A defendant is incompetent to be proceeded against in a criminal action if, as a result of mental illness, disease or defect, he is unable

(1)to understand the nature of the proceedings,

(2)to assist and cooperate with his counsel,

(3)to follow the evidence, or

(4)to participate in his defense.

(b)A defendant is incompetent to be sentence if, as a result of mental illness, disease or defect, he is unable

(1)to understand the nature of the proceedings,

(2)to understand the charge of which he has been convicted,

(3)to understand the nature and extent of the sentence imposed upon him or

(4)to assist and cooperate with his counsel.