Psych and the Law
Detecting truth and lies
A. Detecting truth and lie
- Polygraphs- one of most common methods for determine lies
- Polygraphs detect lies by detecting reparation, blood pressure, skin response, heart
rate, movement...physiological response
- Not detecting if telling lie, detecting if physiological changes in body.
- What about someone with high blood pressure? Someone who is just a nervous/
- Not a lot of standardization of administering polygraph. This is one of the big
B. Administering the polygraph-
- First thing done is saying, “if you lie, this machine will know.”
- This is a standard instruction.
- Used to make person nervous.
- Control question test- requires the administer give two types of test
- First type- relative questions about the crime
- Second type- “control type” about common misdeeds. Ex: “have you ever stolen
anything prior to the age of 21?”
- Considered control questions in which most people would answer yes to.
- Assumes that innocent people will lie to common misdeed questions. They will get
nervous, and get a baseline to physiological spike
- Looking for what lie looks like. - Point is- innocent person nervous about misdeed questions and not nervous about
- Guilty person would be nervous about relevant questions, and not nervous about
- Directed lie test- variation on control question test.
- But subject told to lie about control questions.
- Based on the assumption that the guilty person thinks the examiner will know what
it looks like when they lie.
- Guilty knowledge test- goal is not to have person lie to anything
- Instead administer is trying to detect what knowledge the person has
- Administer asks question and gives multiple choice answers
- Watches device and watches device for spikes during multiple choice questions.
- Ex: Knife was found by a. bed b. by back door c. by hedge
- Done slowly so that administer can mark physiological response. Goal is to see spike
when person hears right answer.
- Don’t even have to answer question.
- Assumes that innocent person hasn’t heard any information about the case. Has to
be info that hasn’t been released