Recently posted to SSRN (and forthcoming in the Journal of Empirical Legal Studies):
Michael J. Saks
, Arizona State University (ASU) - Sandra Day O'Connor College of Law; N. J. Schweitzer, Arizona State University; Eyal Aharoni, University of California, Santa Barbara - Department of Psychology; and Kent Kiehl, University of New Mexico
recent research has found that neurological expert testimony is more
persuasive than other kinds of expert and non-expert 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; non-image 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 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 non-image neurological. But when the expert evidence included neuroimages, jurors moved in the direction argued by counsel.