PSYC 372 Exam 3 Study Guide

Defining Insanity

• Refers to a mental state at time of offense (legal term not a psychological term)

• Not a clinical diagnosis

• A person can be mentally ill but legally sane, or legally insane without a DSM disorder

• May involve cognitive impairments, brain injury, or other “defects” not classified as mental illness.

Andrea Yates Case*

• Texas state court used the M’Naghten type insanity standard

• Despite extensive psychiatric history and evidence of postpartum psychosis, the jury rejected the insanity defense and found her guilty of capital murder

  • She remains in psychiatric facility

Mens rea

guilty mind

Actus rea

guilty act 

Irresistible Impulse Test

• Expands M’Naghten definition of insanity 

• It allows the defendant to argue that even if they knew the act was wrong, they were unable to control their actions due to a mental disorder.

The M’Naghten Rules

• Mental disease or defect of the mind? If yes:

  • Did not know the nature and quality of the act 

    • OR 

  • Did not know it was wrong. 

• M’Naghten: Not guilty

American Law Institute (ALI) rule

• A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity to either appreciate the criminality of his conduct or to corform to his conduct to the requirements of law. 

• Because of a mental disease or defect do they lack substantial capacity to _____. 

  • Know right from wrong? 

    • OR 

  • Control themselves to follow the law? 

• ALI: Not Guilty 

The frequency and success of insanity defense

• Used in less than 1% of all felony cases and fails in over 70% of these cases. 

• Less than 1/3 involves victim death 

• NGRI defendants spend slightly longer custody than those who do not use defense