The Impact of Neuroimages in the Sentencing Phase of Capital Trials

• Author: Kent A. Kiehl,Eyal Aharoni,N. J. Schweitzer,Michael J. Saks
• Published date: 01 March 2014
• DOI: http://doi.org/10.1111/jels.12036
• Date: 01 March 2014

The Impact of Neuroimages in the

Sentencing Phase of Capital Trials

Michael J. Saks, N. J. Schweitzer, Eyal Aharoni, and Kent A. Kiehl*

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.

I. Introduction

A. Expectations of Inordinate Effects of Neuroimages

In criminal trials, brain images are among the most recent forms of evidence presented for

the purpose of supporting factual arguments about the defendant’s mental condition. That

images would enhance persuasion should not be surprising when we consider the sizeable

*Address correspondence to Michael Saks, Sandra Day O’Connor College of Law, Arizona State University, Box

877906, Tempe, AZ 85287-7906, email: saks@asu.edu. Saks is Regents Professor in the College of Law and Department

of Psychology; Schweitzer is Assistant Professor of Social and Behavioral Sciences, New College of Interdisciplinary

Arts and Sciences, Arizona State University; Aharoni was Postdoctoral Fellow at the University of New Mexico and is

now Associate Behavioral Scientist, RAND Corporation; Kiehl is Associate Professor of Psychology and Neuroscience,

University of New Mexico.

This research was supported by a grant from the John D. and Catherine T. MacArthur Foundation to the Law and

Neuroscience Project.

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Journal of Empirical Legal Studies

Volume 11, Issue 1, 105–131, March 2014

105

body of research finding that images enhance learning compared to textual-only commu-

nication in educational settings (Carney & Levin 2002; Mayer 2009).

Numerous commentators have expressed concern that these images are inordinately

persuasive—far more so than the life history of the defendant, or the interview-based

diagnoses of a clinical psychologist or psychiatrist, or the tests of a neuropsychologist, or

even a radiologist’s verbal description of the findings of an MRI or fMRI. The notion that

has been advanced is that seeing the image of a brain with their own eyes leads judges and

jurors to believe something that they will be unable to deny: that the suspect’s brain appears

different, that the observed difference is beyond the control of the defendant, and—at the

end of this line of reasoning or intuition—that the extreme behavior that brought the

defendant to court is not something for which he or she can be held responsible. In this

view, if the brain is the source of behavior, then a defective brain must be the cause of the

deviant behavior. The image, and only the image, it has been suggested, can lead judges

and jurors to this unshakable conclusion (e.g., Batts 2009; Brown & Murphy 2010; Compton

2010; Dumit 1999; Gurley & Marcus 2008; Khoshbin & Khoshbin 2007; Kulynych 1997; Pratt

2005; Rose 2000; Roskies 2007, 2008).

If brain images have far more influence on factfinders than is justified by the

information those images convey, then the courts will be asked to exclude such images.

Rule 403 of the Federal Rules of Evidence, and similar or identical rules in all states,

provides that otherwise relevant evidence “may be excluded if its probative value is sub-

stantially outweighed by the danger of unfair prejudice, confusion of the issues, or mislead-

ing the jury . . . .” Courts prefer admission of relevant evidence, so exclusion on these

grounds is unusual, but if neuroimages were found to routinely win the acquiescence of

jurors despite adding little or nothing to the information provided by a witness using other

means to explain the findings of an examination of a defendant or, indeed, if the

neuroimages somehow turned the tide in circumstances where evidence in other forms was

not terribly persuasive, then the images would be serious candidates for exclusion.

The neurosciences are revealing growing evidence for neural markers of poor

behavioral control (Aharoni et al. in press) and biomarkers for mental illnesses like schizo-

phrenia (Du et al. 2012) and psychopathy (Ermer et al. 2012, 2013), but it is not the case

that just any neural cause of antisocial behavior is sufficient to legally excuse that behavior.

The ongoing challenge for neuroscientists and lawyers is to reliably distinguish legally

excusable neural causes from inexcusable ones, and to present this information in an

unbiased manner. To date, there is no clear consensus on what criteria ought to be used in

the performance of such tasks.

Moreover, brain images created from techniques such as functional MRI (fMRI) are

the product of a complex set of choices and manipulations: the scanner, its programming,

its measures, the tasks selected for testing patients and subjects, the characteristics of the

sampled participants, the analyses carried out on the resulting time-series data, and the

soundness of the statistics used in the analysis. Interpretation of what constitute abnormal

patterns might require comparison to a normative database. Unfortunately, such normative

databases are rare. Further, many brain functions, and certainly brain structure, change

over time, so a test today may not necessarily tell us anything about acute brain function

(i.e., a psychotic event) at the time of the conduct at issue in a criminal case. In short, no

106 Saks et al.