Although recent research has found that neurological expert testimony is more persuasive than other kinds of expert and nonexpert evidence, no impact has been found for neuroimages beyond that of neurological evidence sans images. Those findings hold true in the context of a mens rea defense and various forms of insanity defenses. The present studies test whether neuroimages afford heightened impact in the penalty phase of capital murder trials. Two mock jury experiments (n=825 and n=882) were conducted online using nationally representative samples of persons who were jury eligible and death qualified. Participants were randomly assigned to experimental conditions varying the defendant's diagnosis (psychopathy, schizophrenia, normal), type of expert evidence supporting the diagnosis (clinical, genetic, neurological sans images, neurological with images), evidence of future dangerousness (high, low), and whether the proponent of the expert evidence was the prosecution (arguing aggravation) or the defense (arguing mitigation). For defendants diagnosed as psychopathic, neuroimages reduced judgments of responsibility and sentences of death. For defendants diagnosed as schizophrenic, neuroimages increased judgments of responsibility; nonimage neurological evidence decreased death sentences and judgments of responsibility and dangerousness. All else equal, psychopaths were more likely to be sentenced to death than schizophrenics. When experts opined that the defendant was dangerous, sentences of death increased. A backfire effect was found such that the offering party produced the opposite result than that being argued for when the expert evidence was clinical, genetic, or nonimage neurological, but when the expert evidence included neuroimages, jurors moved in the direction argued by counsel.
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