Does seeing a criminal's brain affect jury decisions?
Edith Greene and Brian Cahill ask this question in a new study which put volunteers in the position of jurors in a murder trial. The 'defendant' was guilty, but the question was: should they get life in prison, or death?
It turned out that seeing brain scans didn't have much of an effect - but it's not clear how far the results would generalize.
208 mock-jurors were randomly assigned to get different kinds of mitigation information about the accused. Sometimes, all they were told was that he had been diagnosed with schizophrenia, depression and a substance misuse disorder. Others were also given neuropsychological test scores showing that he did poorly on various tests of reasoning and cognition. Finally, some were shown brain scans on top of all that, scans which were described as showing left frontal lobe damage.
All these materials were based on a real 2007 court case.
What happened? When the defendent was said to have been assessed as probably "dangerous" in future, people who were only told his diagnosis of schizophrenia usually sent him to the chair. But when they were given his psychological test scores - showing that he suffered from cognitive impairments - they were far more lenient. Seeing the neuroimages had no effect on top of that.
This suggests that brain scans don't exert a seductive allure on jury decisions, at least not over-and-above psych test scores. But I'm not sure how representative the results are. The 'jurors' were all psychology undergrads. Most were Hispanic (63%) females (67%). Are psychology students especially resistant to the allure of brain scans - and/or especially vulnerable to the allure of psychological test scores? No-one knows, but it's surely plausible.
On some level, neuroimaging evidence clearly can influence people's decisions, like any other evidence; lawyers wouldn't bother presenting it otherwise. The question is how much of an impact it has, but that is surely going to depend on the details of the case as well as the juror's background; I'm not sure how much a study like this one, focussing on one example, will be able to tell us.
Greene E, and Cahill BS (2011). Effects of Neuroimaging Evidence on Mock Juror Decision Making. Behavioral Sciences and the Law PMID: 22213023
6 comments:
I am surprised that a diagnosis of serious mental illness on it's own would not be enough to stop a death sentence.
Could the situation described actually happen in reality?
Isn't the real story here that a majority would send someone with confirmed schizophrenia to the chair? Does any state even do that?
Well, this was all based on a real case: William Sablan. In 1999 he killed (and bloodily dismembered) his cellmate. He suffered from schizophrenia and head injuries. He was given life without parole after 11 out of 12 jurors voted for death (they needed 100%), in Colorado.
2/3 of a group that should probably be the most aware of the implications of their decision vote to send a man to death?
This study certainly makes me lose all faith in humanity...
The fact that the brain imaging data didn't sway the jury, even if within a small (and biased) sample of the population has strong implications for neuroimaging research. It may sound strange, but many scientists are aware of the ethical implications of their research. Findings can be exaggerated or misinterpreted and in the wrong hands, they can be sold for the wrong purposes. Some of us are aware that 'science is the new mythology'; the news bytes make study results sound like facts. This is despite of a fact that everyone knows: 1. research findings are derived from averages i.e. they summarise inter individual differences into numbers and can be never be generalised to the individual, 2. scientific findings are highly dependent on experimental context, this is especially true for neuroimaging where the subject missing his morning coffee can tip the results in one way or the other. It is good to know that psych undergrads knew better. Flashy brain pictures need to be supported with multiple complementary analysis and the findings need to be reproduced in multiple labs before we can affirm their validity.
You may also find this article interesting, though it could use a real explanation:
http://psr.sagepub.com/content/3/3/254.short
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