The Impact of Neuroimages in the Sentencing Phase of Capital Trials
Addressing the concern that neuroimages used in criminal trials could be inordinately persuasive on jurors, The Mind Research Network's Kent A. Kiehl, PhdD, and his co-authors tested whether the introduction of neuroimages did in fact have a greater impact when presented during the penalty phase of a capital murder trial. Their findings were recently reported in their paper, The Impact of Neuroimages in the Sentencing Phase of Capital Trials. The researchers used two experiments to evaluate if neuroimage evidence had any mitigating impact on the sentence handed down by a representative sample of more than 820 jury-eligible, death-qualified mock jurors. Both experiments compared the introduction of neuroimages against three other forms of evidence that led to the same diagnosis: (1) neuroscience expert testimony without brain images, (2) expert testimony of the defendant’s genetic abnormality, and (3) expert testimony based on a clinical psychological examination. The researchers also presented the case to a control group of jurors that saw the facts without the introduction of any expert testimony.
The first experiment evaluated the four types of expert testimony presented and the absence of expert testimony when crossed with a defendant diagnosed with psychopathy, schizophrenia, or “healthy” as additional independent variables. The researchers found that for the healthy defendant, the introduction of neuroimage evidence did not affect the jurors’ decision differently than the nonimage-based evidence. For defendants diagnosed with psychopathy, however, the introduction of neuroimage evidence did decrease the jurors’ judgment of the defendant’s responsibility, but did not decrease the future dangerousness assessment and only marginally decreased the imposition of the death penalty. For the defendant diagnosed with schizophrenia, the neuroimage evidence significantly increased the jurors’ perception of the defendant’s responsibility but did not correspondingly increase the percent of death sentences imposed.
The second experiment added an additional element to the same structure as the first experiment: whether the expert testimony was offered by the prosecution as evidence of an aggravating factor supporting a death verdict or if it was offered by the defense as mitigating evidence in hopes of a sentence of life-in-prison as opposed to death. Of note, the researchers found that when neuroimage evidence was presented by the defense, it did have the effect of reducing the rate of death sentences in comparison to presentations of clinical, genetic, and nonimage neurological evidence. In comparison, when the prosecution was the party introducing the neuroimaging evidence, the jury was more likely to impose the death penalty. The researchers concluded that, “[f]or both [prosecution and defense], the neuroimage evidence was the most persuasive, advancing their arguments and moving verdicts in the direction they sought.”
The researchers also found that while defendants diagnosed with psychopathy were more likely to be sentenced to death than those diagnosed with schizophrenia, the neuroimage evidence had the effect of reducing judgments of responsibility and death sentences for psychopaths only. In fact, when jurors were presented with neuroimage evidence of schizophrenia in a defendant, jurors were more likely to assign responsibility to those defendants. In contrast, when presented with nonimage neuroscience of schizophrenia in the defendant jurors assigned less responsibility and less dangerousness to the defendant and decreased the number of death sentences.