Table 1 Summary of key variables for each reviewed study
No expert neuroscientific testimony vs. Expert neuroscientific testimony without neuroimages | ||||||||||
Study | Number of Participants | Legal Judgment | Crime | Condition: No expert neuroscientific testimony | Condition: Expert neuroscientific testimony without neuroimages (Expert) | Expert Type | Additional Independent Variables | Additional Dependent Variables | Effect on Verdict | Effect on Sentence |
Saks et al., 2014 - Experiment 1 | 825 | Death/Life sentence | First degree murder | No diagnosis or neuroscientific evidence | Two neuroscientists affirmed the mental disorder diagnosis based on fMRI scans of the defendant’s brain | Neuroscientists | Diagnosis: Schizophrenia vs. psychopathy vs. healthy | Responsibility, dangerousness | N/A | Yes: Reduced death sentences, only for defendants with Schizophrenia |
Greene & Cahill, 2012 | 208 | Death/Life sentence | First degree murder | Neuropsychologist testified to defendant’s psychosis diagnosis | Neuropsychologist testified to psychosis diagnosis and reported cognitive deficits suggesting frontal brain damage | Neuropsychologist | Defendant dangerousness: low vs. high risk | Responsibility, self-control, dangerousness, influence of expert testimony | N/A | Yes: Reduced death sentences, only for high risk defendants |
Schweitzer et al., 2011 - Experiment 1 | 237 | Verdict (first-degree/second-degree/manslaughter/not guilty) + Sentence | Armed robbery + homicide | Defense attorney claimed defendant suffered from a neurological defect preventing him from forming the requisite intent. | Neuroscientist claimed that the defendant suffered from structural frontal lobe damage, preventing him from being able to premeditate and deliberate about, or form the intent to be guilty of, first or second degree murder. He was also prone to losing control and becoming enraged. | Neuroscientist | N/A | N/A | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Experiment 2 | 294 | Verdict (guilty/not guilty) + Sentence | Robbery + assault | Defense attorney claimed defendant suffered from a neurological defect preventing him from forming the requisite intent. | Neuroscientist claimed that the defendant suffered from structural frontal lobe damage, preventing him from being able to premeditate and deliberate about, or form the intent to be guilty of, first or second degree murder. He was also prone to losing control and becoming enraged. | Neuroscientist | N/A | Responsibility, self-control | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Experiment 3 | 512 | Verdict (simple assault/aggravated assault/not guilty) + Sentence | Assault | Defense attorney claimed defendant suffered from a neurological defect preventing him from forming the requisite intent. | Neuroscientist claimed that the defendant suffered from structural or functional frontal lobe damage, preventing him from being able to premeditate, or form the intent to be guilty of, first or second degree murder. He was also prone to losing control and becoming enraged. | Neuroscientist | N/A | Responsibility, self-control | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Experiment 4 | 433 | Verdict (simple assault/aggravated assault/not guilty) + Sentence | Assault | Defense attorney claimed defendant suffered from a neurological defect preventing him from forming the requisite intent. | Neuroscientist claimed that the defendant suffered from structural frontal lobe damage, preventing him from being able to premeditate and deliberate about, or form the intent to be guilty of, first or second degree murder. He was also prone to losing control and becoming enraged. | Neuroscientist | N/A | Responsibility, self-control | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Meta-analysis | 1374 | Meta-analysis | Meta-analysis | Meta-analysis | Meta-analysis | Meta-analysis | N/A | Responsibility, self-control | No: No change in verdict | No: No change in sentence |
Mowle et al., 2016 | 419 | Guilty/Not guilty + Sentence | Robbery + assault | Psychologist testified to defendant’s mental disorder and traumatic brain injury (Condition 2). | Psychologist testified to defendant’s diagnosis and damage to prefrontal cortex, predisposing him to impulsivity (Condition 3). | Psychologist | Diagnosis: Schizophrenia vs. psychopathy | N/A | No: No change in verdict | No: No change in sentence |
Allen et al., 2019 | 330 | Sentence | Sexual assault | Psychologists diagnosed defendant with an impulse control disorder | Neurologists had located a large tumor in the “impulse control” region of the defendant’s brain | Neurologists | Treatment/dangerousness: treated and low risk of future dangerousness vs. untreatable and high risk of future dangerousness | Responsibility, self-control, importance of expert testimony | N/A | Yes: Reduced length of prison sentences |
LaDuke et al., 2018 | 896 | Sentence | Burglary + aggravated assault | Facts of case (mock police report of the crime, defendant statement, defendant plea); allusion to family and friend statement in support of defendant. | [VIDEO] Psychologist described the defendant’s neurological abnormalities, based on MRI/fMRI scans, and concluded that the defendant posed a high risk for future violence. | Psychologist | Structural vs. functional neuroimaging | Culpability, dangerousness, influence of expert testimony | N/A | No: No change in sentence |
Marshall et al., 2017 - Experiment 2 | 400 | Sentence | Murder | Psychiatrist discussed psychological interview methods for psychopaths, testified that the defendant exhibited a lack of impulse control and feelings of guiltlessness, explained characteristics of psychopaths. | Neuroscientist discussed fMRI research and psychopathy measurement techniques for psychopaths, testified that the defendant exhibited underactivation in amygdala and orbitofrontal cortex, explained characteristics of psychopaths. | Neuroscientist | N/A | Self-control, dangerousness, influence of expert testimony | N/A | No: No change in sentence |
No expert neuroscientific testimony vs. Expert neuroscientific testimony with neuroimages | ||||||||||
Study | Number of Participants | Legal Judgment | Crime | Condition: No expert neuroscientific testimony | Condition: Expert neuroscientific testimony with neuroimages (Expert+Neuroimage) | Expert Type | Additional Independent Variables | Additional Dependent Variables | Effect on Verdict | Effect on Sentence |
Saks et al., 2014 - Experiment 1 | 825 | Death/Life sentence | First-degree murder | No diagnosis or neuroscientific evidence | Expert + fMRI | Neuroscientists | Diagnosis: Schizophrenia vs. psychopathy vs. healthy | Responsibility, dangerousness | N/A | No: No change in death sentences |
Greene & Cahill, 2012 | 208 | Death/Life sentence | First-degree murder | Neuropsychologist testified to defendant’s psychosis diagnosis | Expert + MRI and PET with descriptions of behavioral implications. | Neuropsychologist | Defendant dangerousness: low vs. high risk | Responsibility, self-control, dangerousness, influence of expert testimony | N/A | Yes: Reduced death sentences, only for high risk defendants |
Appelbaum et al., 2015 - Experiment 3 | 763 | Death/Life sentence | First-degree murder | Defense attorney claimed that the defendant’s act was impulsive | Psychiatrist testified that neuroimage showed a brain abnormality which led the defendant to act impulsively. Presented MRI. | Psychiatrist | Crime heinousness: low vs. high | Dangerousness, self-control | N/A | Yes: Reduced death sentences |
Schweitzer et al., 2011 - Experiment 1 | 237 | Verdict (first-degree/second-degree/manslaughter/not guilty) + Sentence | Armed robbery + homicide | Defense attorney claimed defendant suffered from a neurological defect preventing him from forming the requisite intent. | Expert + fMRI | Neuroscientist | N/A | N/A | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Experiment 2 | 294 | Verdict (guilty/not guilty) + Sentence | Robbery + assault | Defense attorney claimed defendant suffered from a neurological defect preventing him from forming the requisite intent. | Expert + fMRI | Neuroscientist | N/A | Responsibility, self-control | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Experiment 3 | 512 | Verdict (simple assault/aggravated assault/not guilty) + Sentence | Assault | Defense attorney claimed defendant suffered from a neurological defect preventing him from forming the requisite intent. | Expert + MRI and fMRI | Neuroscientist | N/A | Responsibility, self-control | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Experiment 4 | 433 | Verdict (simple assault/aggravated assault/not guilty) + Sentence | Assault | Defense attorney claimed defendant suffered from a neurological defect preventing him from forming the requisite intent. | Expert + MRI | Neuroscientist | N/A | Responsibility, self-control | Yes: Reduced verdict severity | No: No change in sentence |
Schweitzer et al., 2011 - Meta-analysis | 1374 | Meta-analysis | Meta-analysis | Meta-analysis | Meta-analysis | Meta-analysis | N/A | Responsibility, self-control | Yes: Reduced guilty verdicts | No: No change in sentence |
Mowle et al., 2016 | 419 | Guilty/Not guilty + Sentence | Robbery + assault | Psychologist testified to defendant’s mental disorder and traumatic brain injury (Condition 2). | Expert + Brain scan | Psychologist | Diagnosis: Schizophrenia vs. psychopathy | N/A | No: No change in verdict | No: No change in sentence |
LaDuke et al., 2018 | 896 | Sentence | Burglary + aggravated assault | Facts of case (mock police report of the crime, defendant statement, defendant plea); allusion to family and friend statement in support of defendant. | Expert + MRI/fMRI (two neuroimage conditions) | Psychologist | Structural vs. functional neuroimaging | Culpability, dangerousness, influence of expert testimony | N/A | No: No change in sentence |
Appelbaum et al., 2015 - Experiment 1 | 960 | Sentence | Murder | Defense attorney claimed that the defendant’s act was impulsive | Psychiatrist testified that neuroimage showed a brain abnormality which predisposed the defendant to impulsivity and violence. Presented MRI. | Psychiatrist | Crime heinousness: low vs. high | Dangerousness, self-control | N/A | No: No change in sentence |
Schweitzer & Saks, 2011 | 1170 | Guilty/NGRI or GBMI | Assault | Defense attorney argued that the defendant suffered from a mental disorder causing him to act irrationally and uncontrollably. Family testified to neglect and abuse of defendant as a child. | Neurologist testified to MRI showing physical damage to frontal lobe, which could cause defendant to lose control over actions. Presented MRI. Second expert emphasized important of frontal lobe. | Neurologist | N/A | Self-control | Yes: Reduced guilty verdicts | N/A |
Gurley & Marcus, 2008 | 394 | Guilty/NGRI | Murder | Psychologist and psychiatrist testified to defendant’s diagnosis | Psychologist and psychiatrist testified to diagnosis and presented 4 MRI scans showing prefrontal cortex damage, which likely contributed to difficulty with impulse control. | Psychologist and psychiatrist | Diagnosis: Psychosis (schizophrenia) vs. psychopathy | Influence of expert testimony | Yes: Reduced guilty verdicts | N/A |
Expert neuroscientific testimony without neuroimages vs. Expert neuroscientific testimony with neuroimages | ||||||||||
Study | Number of Participants | Legal Judgment | Crime | Condition: Expert neuroscientific testimony without neuroimages (Expert) | Condition: Expert neuroscientific testimony with neuroimages (Expert+Neuroimage) | Expert Type | Additional Independent Variables | Additional Dependent Variables | Effect on Verdict | Effect on Sentence |
Saks et al., 2014 - Experiment 1 | 825 | Death/Life sentence | First degree murder | Two neuroscientists affirmed the mental disorder diagnosis based on fMRI scans of the defendant’s brain | Expert + fMRI | Neuroscientists | Diagnosis: Schizophrenia vs. psychopathy vs. healthy | Responsibility, dangerousness | N/A | No: No change in death sentences |
Greene & Cahill, 2012 | 208 | Death/Life sentence | First-degree murder | Neuropsychologist testified to psychosis diagnosis and reported cognitive deficits suggesting frontal brain damage | Expert + MRI and PET with descriptions of behavioral implications. | Neuropsychologist | Defendant dangerousness: low vs. high risk | Responsibility, self-control, dangerousness, influence of expert testimony | N/A | No: No change in death sentences |
Schweitzer et al., 2011 - Experiment 1 | 237 | Verdict (first-degree/second-degree/manslaughter/not guilty) + Sentence | Armed robbery + homicide | Neuroscientist claimed that the defendant suffered from structural frontal lobe damage, preventing him from being able to premeditate and deliberate about, or form the intent to be guilty of, first or second degree murder. He was also prone to losing control and becoming enraged. | Expert + fMRI | Neuroscientist | N/A | N/A | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Experiment 2 | 294 | Verdict (guilty/not guilty) + Sentence | Robbery + assault | Neuroscientist claimed that the defendant suffered from structural frontal lobe damage, preventing him from being able to premeditate and deliberate about, or form the intent to be guilty of, first or second degree murder. He was also prone to losing control and becoming enraged. | Expert + fMRI | Neuroscientist | N/A | Responsibility, self-control | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Experiment 3 | 512 | Verdict (simple assault/aggravated assault/not guilty) + Sentence | Assault | Neuroscientist claimed that the defendant suffered from structural or functional frontal lobe damage, preventing him from being able to premeditate, or form the intent to be guilty of, first or second degree murder. He was also prone to losing control and becoming enraged. | Expert + MRI and fMRI | Neuroscientist | N/A | Responsibility, self-control | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Experiment 4 | 433 | Verdict (simple assault/aggravated assault/not guilty) + Sentence | Assault | Neuroscientist claimed that the defendant suffered from structural frontal lobe damage, preventing him from being able to premeditate and deliberate about, or form the intent to be guilty of, first or second degree murder. He was also prone to losing control and becoming enraged. | Expert + MRI | Neuroscientist | N/A | Responsibility, self-control | No: No change in verdict | No: No change in sentence |
Schweitzer et al., 2011 - Meta-analysis | 1374 | Meta-analysis | Meta-analysis | Meta-analysis | Meta-analysis | Meta-analysis | N/A | Responsibility, self-control | No: No change in verdict | No: No change in sentence |
Mowle et al., 2016 | 419 | Guilty/Not guilty + Sentence | Robbery + assault | Psychologist testified to defendant’s diagnosis and damage to prefrontal cortex, predisposing him to impulsivity. | Expert + Brain scan | Psychologist | N/A | N/A | No: No change in verdict | No: No change in sentence |
LaDuke et al., 2018 | 896 | Sentence | Burglary + aggravated assault | [VIDEO] Psychologist described the defendant’s neurological abnormalities, based on MRI/fMRI scans, and concluded that the defendant posed a high risk for future violence. | Expert + MRI/fMRI (two neuroimage conditions) | Psychologist | Structural vs. functional neuroimaging | Culpability, dangerousness, influence of expert testimony | N/A | No: No change in sentence |
Marshall et al., 2017 - Experiment 1 | 758 | Sentence | Murder | Neuroscientist discussed fMRI research and psychopathy measurement techniques for psychopaths, testified that the defendant exhibited underactivation in amygdala and orbitofrontal cortex, explained characteristics of psychopaths. | Expert + fMRI | Neuroscientist | N/A | Self-control, dangerousness, influenced by expert testimony | N/A | No: No change in sentence |
Schweitzer & Saks, 2011 | 1170 | Guilty/NGRI or GBMI | Assault | Neurologist testified to MRI showing physical damage to frontal lobe, which could cause defendant to lose control over actions. Second expert emphasized important of frontal lobe. | Expert + MRI | Neurologist | N/A | Self-control | No: No change in verdict | N/A |
Baker et al., 2013 | 73 | Guilty/Not guilty | Assault | Neurologist testified that an MRI revealed frontal lobe damage and that such damage could impair impulse control. Presented bar graph comparing normal brain activity to defendant’s brain activity. | Neurologist testified that an MRI revealed frontal lobe damage and that such damage could impair impulse control. Presented MRI scans of normal brain and defendant’s brain. | Neurologist | N/A | Dangerousness | No: No change in verdict | No: No change in degree of punishment |