1. Opposing Expert Witnesses and Neuroscientific Evidence
I am going to present two experiments which examined the influence of neuroscientific evidence when provided by opposing expert witnesses.
Riquel Hafdahl & N.J. Schweitzer

2. The Neuroimage Bias Are neuroimages unduly persuasive?
1st wave of research said yes (McCabe & Castel, 2008; Gurley & Marcus, )
2nd wave of research said no (Schweitzer et al. 2011; Gruber & Dickerson, )
Why the discrepancy?
Time – Neuroimage novelty has subsided
Study design
The potential undue influence that neuroimages may have is known as the neuroimage bias and the first studies to examine this did find support for a biasing effect. But, a second larger wave of research did not find evidence of such a bias.
One possible explanation for this discrepancy may be found in the study design.

3. The Neuroimage Bias Is study design a factor?
Between-subjects = no bias
Within-subjects = bias
Between-subjects = absolute judgments
Within-subjects = relative judgments
Most of the previous studies that have not found a bias used between-subjects designs and the studies that did find a bias used within-subjects designs. One reason for this discrepancy may be the difference in tasks-- in that one employs absolute judgments and the other, relative judgments. In the within- subjects designs, by giving participants a basis of comparison, a contrast effect is being created.

4. The Present Studies
Does a neuroimage bias occur among jurors in situations of relative judgment?
Study 1 = Criminal case
Study 2 = Civil case
The purpose of the present studies was to asses if a neuroimaging bias could be found among mock jurors, and if such bias is dependent on study design. This was done through the use of opposing experts testifying in court cases.

5. Study 1 Method
Participants (n = 439) read mock criminal assault case on Mturk
56.1% Male, 79.9% Caucasian, Mage = 33.05, SDage = 10.67
Attention Checks removed ~25 participants (<75% on recall quiz)
Participants from previous related studies excluded
Randomly assigned to conditions:
One Expert (Defense): Brain vs. Graph
Two Experts: Dbrain-Pgraph / Dgraph-Pbrain / Graph-Graph / Brain-Brain DV
Punishment Recommendation
In Study 1, participants read a criminal court case in which the defendant assaulted his neighbor. The defense had an expert witness testify that an fMRI of the defendants brain showed evidence of decreased functioning in his frontal lobe, resulting in uncontrollable behavior and therefore he should not be held accountable. The prosecution argued that this was not true and, in the conditions with two experts, offered their own expert with an independent fMRI to show this. The evidence type that the experts had varied between being either a graph or a brain image of the fMRI results.
The primary DV was punishment recommendations. We also measured verdict, but the case was written in such a way that the defendant’s guilt was clear, so the real question was if the neuroimage was mitigating and impacted punishment severity.

6. Study 1 Results - Single Expert
When there was a single expert (always for the defense), there was no significant difference in punishment recommendations based on the presence / absence of a neuroimage.
This is consistent with most of the recent findings on neuroimage effects.
p = .729
As expected, In the conditions with only one expert witness, we did not find a significant difference in punishment severity based on the presence or absence of a neuroimage.

7. Study 1 Results - Opposing Experts
When there were opposing experts:
Defense Brain / Prosecution Graph
Prosecution Brain / Defense Graph
There was a significant difference between the conditions, with the punishment recommendations leaning toward the side presenting the neuroimage.
*p = .007 ηp2 = .06
Now, in the conditions where two experts testified, we found that punishment severity was affected in that it shifted, leaning toward whichever side presented the image. So, when the defense had the neuroimage, the mean punishment severity was 3.7 which was significantly less than when the prosecution had the image—the mean punishment severity here was 4.47.

8. Study 2 Overview Extend to a Civil Context
Neuroimages / Neuroscience increasing in prevalence in civil cases
To demonstrate some sort of physical injury
As evidence of physical pain
As evidence of emotional / psychological pain
The use of neuroscientific evidence, and neuroimages in particular appears to be on the rise in civil cases, and specifically in personal injury cases, as a tangible way to demonstrate injury and chronic pain. Because of this…for Study 2, we aimed to explore the neuroimage bias in a personal injury case context.

9. Study 2 Method
Participants (n = 275) read mock civil personal injury case on Mturk – Car accident left Plaintiff with permanent leg pain.
61.3% Male, 78.8% Caucasian, Mage = 33.75, SDage = 10.31
Participants from Study 1 Excluded from Study 2
Randomly assigned to 1 of 5 conditions
One Expert (Plaintiff): Brain Image vs. Graph
Two Experts: Plaintiff Brain Image / Defense Graph vs. Plaintiff Graph / Defense Brain Image
Control: Two Experts, neither has brain image (both have graph)
Order of two experts counterbalanced
DVs:
Verdict Choice
Verdict Certainty (1-10 scale from Plaintiff-Defense)
Participants read a civil court case in which the parties were in a car accident and the plaintiff claimed to have chronic leg pain as a result and was suing the driver of the other car for damages.
The conditions were set up in pretty much the same manner as in Study 1, but here, of course, the expert witnesses either used the fMRI as evidence of increased pain signals in the plaintiff’s brain or as evidence of normal pain signals and thus malingering. The main DVs were simple verdict choice, and verdict certainty.

10. Study 2 - Results
Two experts, where one has a brain image and the other a graph (blue bars): No difference. Majority found for Plaintiff. This does not follow the pattern of Study 1.
However, when compared to a two-expert control where both have graphs (orange bars), verdicts shift with majority finding for Defense.
First we looked at the conditions where there was only one expert testifying, and found no effect on verdict choice or on verdict certainty. This is what we expected and replicates Study 1.
But, In conditions with 2 experts, we did find some interesting differences.
This graph is of verdict choice and the first set of blue bars on the left is when the plaintiff had the image and the blue bars in the middle is when the defense had the image. There was no significant effect on verdict choice between these 2 conditions, which was unexpected and differs from the results of study 1. In both of these conditions, it didn’t seem to matter which expert presented the neuroimage—participants found for the plaintiff between about 65 to 70 percent of the time.
However, when we compared these conditions to a control in which both experts had graphs, which is the orange bars, we did find a significant difference. Verdict choice seemed to flip. When there were 2 experts and both had graphs, participants only found for the Plaintiff about 40 percent of the time.
We also looked at verdict certainty, or confidence, and found the same pattern and it was significant.
These unexpected findings could be an example of the skepticism effect, where having two relatively matched opposing witnesses results in neither being believed. However, this doesn’t fully explain why participants sided with the defense more when neither expert had an image. One possible explanation for this could be that just the mere presence of a neuroimage lends legitimacy to the plaintiffs claim and bolsters their case, even if it is the defense who presents the image.

11. Overall Conclusions
Consistent with recent findings, neuroimagery does not influence juror decisions in situations of absolute judgments (one expert).
In Study 1, we did find some evidence to suggest that relative judgments – as in the case of opposing experts – may induce a preference for neuroimagery.
This effect did not carry through to a civil case, but there are many possible explanations for this.
Different standard of proof, different fact pattern, different images, different decision task (verdict vs punishment). Ongoing research is exploring this.
Overall, it appears that situations of absolute judgments do not induce a neuroimage bias in jurors. This is consistent with recent findings that have failed to find a bias.
We did find evidence of a neuroimage bias in Study 1, in the conditions of relative judgements.
This pattern was not replicated when we changed the context to a civil case though. But, there are many possible explanations for this. The differences between criminal and civil cases are numerous of course but, just the differences in standard of proof and the fact patterns may play a role. Also, we used different images and different decision tasks between the two studies, which may play a role as well.
However, this, to my knowledge is the first experiment to explore the neuroimage bias specifically in a civil case context, so it hopefully can help to serve as a jumping off point for further exploration of the use and possible biasing of neuroimages in civil cases.

12. Implications
Criminal Cases – A neuroimage bias can occur, so include when possible
Civil Cases – A neuroimage bias may occur, but could be problematic
Some general implications and recommendations from this research are that in criminal cases, a neuroimage bias can occur so it may be beneficial to include a neuroimage when possible, and particularly when the opposition is including a neuroimage as evidence.
But, in civil cases a neuroimage bias may occur, but in an unanticipated manner, so it important to note that in situations when only one expert presents a neuroimage, compared to an expert without one, jurors may lean toward the plaintiff, even if it is the defense that presents it. In situations where neither of the opposing experts have neuroimages, jurors may be skeptical of both experts and lean toward the defense.

13. References
Dumit, J. (1999). Objective brains, prejudicial images. Science in Context, 12(01), doi: /S
Gruber, D. & Dickerson, J. A. (2012). Persuasive images in popular science: Testing judgments of scientific reasoning and credibility. Public Understanding of Science 21(8), 938– doi: /
McCabe, D. P. & Castel, A. D. (2008). Seeing is believing: The effect of brain images on judgments of scientific reasoning. Cognition, 107(1), 343–352. doi: /j.cognition
Schweitzer, N. J., Saks, M. J., Murphy, E. R., Roskies, A. L., Sinnott-Armstrong, W., & Gaudet, L. M. (2011). Neuroimages as evidence in a mens rea defense: No impact. Psychology, Public Policy, and Law, 17(3), 357. doi: /a

14. Thank You!
Contact Information:
Riquel Hafdahl
Nick Schweitzer
Program on Law and Behavioral Science