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

-- By MichaelBerkovits - 10 Feb 2008

Introduction

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. Among the many factors that can distort this process are a number of cognitive tendencies that recent work in cognitive psychology predicts to be present in the average juror. At least three factors operate to distort jurors' processing and weighing of the evidence: the tendency to overbelieve eyewitness testimony, to overestimate one's lie-detection abilities, and to overfocus on the crime in question to the exclusion of other, relevant considerations. And at least one factor - the inability to properly interpret the defendant's probability of innocence - warps the application of the reasonable doubt standard.

Weighing the Evidence

Jurors' processing of the evidence presented at trial is handicapped by the systematic shielding of other, relevant information. This information is meta-evidence - information crucial to the interpretation of the trial evidence - and is highly relevant.

Eyewitness Testimony and Faulty Memory

First, jurors receive scant information and no official instruction as to the unreliability of eyewitness testimony. Jurors are repeatedly told, by defense counsel and by the judge, that witnesses may lie; they are essentially never told that witnesses may be "telling the truth" about what they saw and yet still be spewing misinformation. Lawyers undoubtedly make this argument sometimes, but it so violates people's preconceptions that it probably is not worth the effort. Yet modern research shows that memory is notoriously malleable, link, all the more so when the eyewitness was involved in a terrifying or violent crime Schacter excerpt. This would not be a problem if jurors already believed that eyewitness testimony was highly error-prone; instead, jurors come in believing it is the evidentiary gold standard.

Jurors' Lie-Detection Abilities

Similarly, jurors, like all people, believe that are at least decently skilled at telling when someone else is lying. Indeed, given the human tendency to inflate one's perception of one's talents, link, the average juror most likely believes that she is a better-than-average lie detector. Yet, research suggests that ordinary people cannot detect lies at better-than-chance levels: link. Even so, the jury is not told to disregard a witness's demeanor when gauging the truth of what was said. To the contrary, juries may well be encouraged by judges and counsel to take close account of such evidence.

Evidence of Errors by Other Juries

A third meta-evidentiary fact kept from the jury is evidence of errors made by other juries. DNA evidence and confessions by other criminals have exonerated many wrongfully incarcerated defendants, and no one doubts that many wrongfully convicted defendants remain un-exonerated. Unlike the two topics just discussed, jurors' preconceptions in this regard are roughly, if not numerically, accurate. Jurors know that some people innocent of the crime with which they are charged are found guilty. But no judge would instruct a jury to consider this fact. A judge that did might find herself reversed on appeal. Furthermore, defense counsel would clearly be barred from introducing such evidence on relevance grounds. But, of course, if reasonable people applying a "no reasonable doubt" standard get it wrong more than a negligible proportion of the time, then evidence to that effect is highly relevant to a jury made up of such people. Unfortunately, even jurors who consider the fact that erroneous convictions do occur are subject to "focusing" errors: because the primary issue at trial, defense counsels' efforts notwithstanding, is a single (or multiple) bad act by the defendant(s), jurors are prone to view the evidence through that prism and overestimate the strength of the prosecution's case. Jurors might then reason that, even if other cases were wrongly decided, this "strong" case could not fall into that category. (For some examples of modern psychological research on focusing errors, see Gilbert, Kahneman and Tversky (wheel of numbers)).

Underweighting Low Probabilities of Innocence in Applying the Standard of Reasonable Doubt

Among the many recognized formulations of the reasonable doubt jury instructions, Am. Jur. 2nd Trial § 1159, none contain language encouraging the jury to escape the cognitive biases that attend the evaluation of low probabilities. Prospect Theory Prospect Theory suggests that people tend to neglect or underweight outcomes that occur with very small probabilities. Citation Suppose that the sum total of the evidence presented to an ordinary juror at trial suggest, to the juror, a 1% probability that the defendant is actually innocent of the alleged crime. Because jurors underweight low probabilities in their decisionmaking, the juror will tend to "value" this probability at a negligible amount, perhaps zero. A juror in this position would convict. Of course, this violates what most people would want the reasonable doubt standard to do: at least for serious crimes, we would be very uncomfortable knowing that one of every hundred people jailed was innocent.

This problem is endemic to all cases involving low, but not zero, perceived probabilities of innocence. Assume that the jurors in any given trial construct some probability of innocence based on the evidence and that these subjectively-determined probabilities, are in the same ballpark but vary around a mean. In cases where the probability of innocence is low, jurors will systematically underweight those probabilities downward. 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 weighing of the evidence.

An extreme, but possibly justifiable position would be that, knowing that juries made up of 12 reasonable people who had no reasonable doubt as to a defendant's guilt were wrong, it is always wrong for reasonable jurors to convict, because apparently even reasonable people with no reasonable doubt can be mistaken.

Where Does This Leave Us?

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 appears to be a non-starter.

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 "absolutely none, not even a hint of a doubt." This dial-shifting would get at what we presumably want - jury decisions that more closely reflect jurors' actual impressions of the probability of innocence - in a roundabout - and yes, disingenuous - way. Of course, changes like these stem from too cynical a worldview ever to be put into practice.

Third, we can work within the confines of the system. While ordinary people cannot detect lies, experts can do so, both from real-time demeanor and from careful study of facial expressions on videotape link. Is it too fanciful to hope for court-appointed experts, trained by Paul Ekman in truth-detection methods? With respect to eyewitness testimony, it does not seem at all unrealistic to expect that someday soon, we could have a standardized instruction specifically 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.

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