Law in Contemporary Society

Out to Sea in an Ocean of Distortion: Cognitive Psychology in the Jury Box

-- By MichaelBerkovits - 10 Feb 2008


Juries in criminal trials are tasked with processing the evidence adduced at trial and passing it through a special cognitive lens called the "reasonable doubt" standard in order to determine the guilt or innocence of the accused. A number of cognitive tendencies are likely to distort this process. At least two factors operate to distort jurors' processing and weighing of the evidence: the tendencies to overbelieve eyewitness testimony and to overestimate one's lie-detection abilities. And at least two factors infect jurors' application of the reasonable doubt standard: a tendency to overfocus on the crime in question and to ignore prior, wrongful convictions, and the inability to properly interpret the defendant's probability of innocence.

Weighing the Evidence

Eyewitness Testimony and Faulty Memory

People effortlessly believe what they hear. Gilbert. With some effort, jurors accept that some witnesses are lying about their recollections. However, jurors are almost never told that witnesses may be "telling the truth" about what they saw and yet still be spewing misinformation. Yet modern research shows that memory is notoriously malleable (Loftus), all the more so when the testimony regards a terrifying or violent crime (Schacter, p. 114).

Jurors' Lie-Detection Abilities

People believe they are somewhat skilled at telling when someone else is lying. Indeed, the average juror probably believes that she is a better-than-average lie detector (Taylor & Brown). Yet, research suggests that ordinary people cannot detect lies at better-than-chance levels (Ekman). Despite this, jurors are encouraged, by judges and counsel, to take close account of a witness's demeanor on the stand in gauging the truth of what was said.

Applying the Reasonable Doubt Standard

Evidence of Errors by Other Juries

A trial creates an artificially narrow focus on one or more bad acts by the defendant. Because directing cognitive focus to a single event can distort decision-making (Gilbert), it would be reasonable to provide juries as much context as possible. Instead, the jury is shielded from evidence of errors made by previous juries, similarly situated. Many convicted individuals have been exonerated in modern legal history. No one doubts that many wrongful convictions go unredressed. Yet evidence and argument going to the frequency of wrongful convictions would be shielded from the jury on relevance grounds. Of course, if reasonable people applying a "no reasonable doubt" standard get it wrong more than a negligible proportion of the time, evidence to that effect is highly relevant to a jury made up of such people. An extreme, but possibly justifiable position would be that it is always incorrect for reasonable jurors to convict: a reasonable doubt is present, by definition, given that past collections of reasonable people with "no reasonable doubt" have been mistaken.

Underweighting Low Probabilities of Innocence

Among the many recognized formulations of the reasonable doubt jury instructions, Am. Jur. 2nd Trial 1159, none encourage jurors to escape the cognitive biases that attend the evaluation of low probabilities. Prospect Theory suggests that people tend to neglect or underweight outcomes that occur with very low probabilities (Cf. here); yet defendants whose trials indicate a low, but non-zero probability of innocence are the ones the reasonable doubt standard was designed to protect.

Suppose that the evidence presented at trial suggests a 1% probability that the defendant is innocent. Because people undervalue low probabilities when making decisions, a juror will tend to value this probability at a negligible amount, perhaps zero, and therefore convict. This violates what most people want the reasonable doubt standard to do; at least for crimes with serious consequences, we would be uncomfortable knowing that one of every hundred people jailed was innocent.

This problem is endemic to all cases involving low, non-zero, perceived probabilities of innocence. In such cases, jurors will systematically underweight those probabilities. To the extent that subjective determinations of the probability of innocence go into jurors’ decisions of whether or not to acquit, the cognitive tendency to underweight low probabilities will cause more jurors to vote guilty than is justified by their own, subjective calculations of the probability of innocence.

Into the Future

There are at least three approaches to dealing with the issues highlighted.

First, we could scrap the jury system entirely and rework the criminal justice system from the ground up. This is a non-starter, at present.

Second, we can recognize and work with the realization that the criminal justice system is not intended to be a truth-finding system, but rather a mechanism that provides us with the modicum of comfort necessary to live with incarcerating fellow citizens. To the extent that it's all "just a game," we can simply adjust dials upward and downward in order to produce results that make us more comfortable. For example, if we know that jurors systematically underweight low probabilities of innocence, we can instruct them not to apply a "reasonable doubt" standard, but rather a standard of "not even a hint of a doubt." This dial-shifting would presumably get at one thing we want - jury decisions that more closely reflect jurors' actual impressions of the probability of innocence - in a roundabout, disingenuous way. But this approach is too cynical to be put into practice.

Third, we can work within the confines of the system. While ordinary people cannot detect lies, experts can, both from real-time demeanor and from careful study of facial expressions on videotape link. Is it too fanciful to hope for court-appointed, truth-detection experts? Cf. (Ekman). With respect to eyewitness testimony, it does not seem unrealistic to expect that someday soon, we could have a standardized instruction highlighting the difference between "lying" and "telling the truth mistakenly." But such solutions are far from satisfactory. It is too soon to tell whether research in cognitive psychology will have a modest or a revolutionary impact on the criminal justice system, but as recent findings begin the slow process of seeping into the popular consciousness, we are not far from finding out.

  • The thesis of this essay seems to be that the incompatibility between cognitive psychology and jury trial was first noticed yesterday. But we are more than half a century into this particular iteration of the discovery that naive juries are defective fact-finders; it's been made several times in the last five hundred years, for a number of different reasons each time. The persistence of the institution is not based on a misguided belief in the accuracy of jury decisions in difficult cases, and was certainly not based on a belief in jury inerrancy. So in order to go beyond the obvious, the essay has to grapple with the real questions: how can the other desirable functions of the jury be attained in an environment of enhanced accuracy, or--if juries are necessary despite their unreliability--what forms of appellate check are desirable. This latter line of questioning, which would directly confront the decline in "sufficiency of evidence" review over the past quarter century, is likely to be particularly fruitful. Innocence Projects, with their close scrutiny of forensic laboratory results, for example, locate failure modes in the process that jury scrutiny will never reveal.


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r14 - 12 Jan 2009 - 23:00:07 - IanSullivan
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