Recently posted to SSRN (and forthcoming in the Journal of Empirical Legal Studies):
"The Impact of Neuroimages in the Sentencing Phase of Capital Trials"
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
Although
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.
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