ABSTRACTSubstantial evidence suggests that jurors rely upon their own conceptions or prototypes of insanity to determine whether a defendant is insane. However, this study is among the first to investigate the nature, variability, and effect of insanity prototypes. First, prototype features were elicited from 81 former prospective jurors. Then, 5 jurors reviewed these features and combined those that they deemed highly similar. Their judgments were used to develop a measure of individual differences in insanity prototypes. Finally, 133 jurors completed this individual differences measure and measures of case-relevant attitudes, and rendered a verdict based on an insanity case vignette.

This research produced three primary findings. First, jurors’ prototypes of insanity are complex and differ from commonly accepted legal standards. Second, despite marked individual differences, there are three identifiable groups of jurors with prototypes that emphasize (1) severe mental disability, (2) a lay conception of “moral insanity,” and (3) characteristics more exclusively related to traditional mental state at the time of the offense concepts. Third, these different prototypes affect the way in which jurors interpret cases and render verdicts. This paper analyzes the implications of these findings for jury selection and the presentation of expert evidence to juries.

INTRODUCTIONBackground and Significance

• The legal system essentially assumes that jurors are blank slates who can select verdicts in an evidence-driven fashion. However, substantial research indicates that jurors have experience-based knowledge structures that guide their legal decision making.

• In cases where defendants raise the controversial defense of insanity, these knowledge structures may strongly jeopardize defendants’ rights to a fair trial by an impartial jury. Research indicates that jurors’ attitudes toward the insanity defense and conceptions of insanity strongly influence their verdicts.

• Research suggests that jurors’ conceptions of insanity affect their judgments, in that jurors: (1) fail to apply legal definitions of insanity in rendering verdicts, and (2) draw different inferences about a defendant’s impairments based on identical case facts. Nevertheless, the nature of jurors’ conceptions and their mechanism of action remains unclear.

Prototype Theory

• To address these issues, this research applies prototype theory, which posits that (1) knowledge about any category is represented by prototype or quintessential member, and (2) category membership is determined based on the extent to which an object’s characteristics match those of the category’s prototype.

• V. Smith found that m.jurors represented crime categories such as “burglary” with prototypes that differed from legal definitions and were more determinative of verdicts than legal definitions.

• Jurors may represent verdict categories in insanity defense cases with prototypes of insanity. A juror may implicitly compare a defendant’s characteristics to those of her prototype of the insane defendant. The more closely his attributes matched those of her prototype, the more likely she would be to judge him a member of the category “insane.”

Purpose, Hypotheses and Design

• Purpose: to determine the nature and variability of jurors’ prototypes of insanity and explore their association with case judgments

• Hypotheses: (1) Jurors have prototypes of insanity that affect their case judgments. (2) There will be individual differences in prototypes of insanity, since categorization results from a learning process.

• Design: Three studies adapt traditional prototype methodology to measure individual differences. Ss were former prospective jurors.

1. Elicited the features of jurors’ conceptions of insanity.

2. Condensed this group of features and developed a measure of individual differences in insanity prototypes.

3. Administered this measure to a sample of jurors to identify individual differences and assess their relationship to case judgments.

STUDIES 1 & 2Feature Elicitation and Reduction

• Study 1: Asked 81 jurors to bring mind their conception of “the typical person who is not responsible for his criminal actions due to mental illness,” then candidly describe his features.

• Study 2: Condensed these descriptions into a set of key prototype features to use in a measure of individual differences:1. Experimenters wrote individual features (N=498) on cards2. To preserve the lay meaning of the features, 5 jurors were asked to use

their judgment to sort the cards into piles of features that meant the same thing to them. When 3/5 jurors agreed that a pair of features were synonymous, the features were combined, producing 57 features.

3. Experimenters assigned labels to these features to capture their essence. These 57 labels became items in the individual differences measure.

Study 2 Results: Individual Differences in Prototype Descriptions

• There are marked individual differences in prototypes. Of the features produced, 35% were idiosyncratic. Only 8% of the remaining features were listed by over 10 jurors.

• Thus, aggregate-based research may “miss the mark.” In order to produce more meaningful results, individual differences must be assessed.

• Note: the prototypes identified in Study 3 are prototypes of “idealized individuals” who fall near the group’s centroid and best capture its key dimensions

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Figure 1. Number of participants contributing to each feature

STUDY 3Identifying Individual Differences in Prototypes

• Administered the Conception Checklist (CC) to 133 jurors. Jurors were asked to bring to mind the prototypical insane person, then rate the extent to which each of the 57 features is important in defining their prototype. For example:

Irrelevant Essential

• Unable to discern right from wrong. 1 2 3 4 5 6 7• Mentally retarded. 1 2 3 4 5 6 7• Violent, angry and hostile to others. 1 2 3 4 5 6 7

• Applied cluster analyses to jurors’ CC scores to identify groups of people with different prototypes. Retained a 3-group solution that was most replicable across methods and subsamples.

• Completed ANOVAs on the features that at least one group rated as important to their prototype (M> 4.6) in order to describe these 3 groups.

Describing Individual Differences in Prototypes

• The nature of the 3 prototype groups is described in Tables 1-4. Table 1 depicts the overlapping features across groups. Features of impaired mental state at the time of the offense and psychosis are important to all 3 prototypes.

• Table 2 depicts the discriminating characteristics of the “Severe Mental Disability” (SMD) prototype of insanity. The SMD prototype is afflicted with extreme, chronic, uncontrollable mental illness and retardation that impairs his ability to function in society.

– Consistent with prior research that suggests that, in the aggregate, jurors’ conceptions of insanity “remain wed to the wild beast test of 1724” (Perlin, 1997, p. 1379). The SMD is deprived of reason to the extent that he is animalistic or childlike, and therefore unworthy of blame.

– However, only 47% of jurors subscribe to the SMD prototype.

• Some 32% of jurors had prototypes that emphasized a lay concept of “Moral Insanity” (MI). Most were women (65%). The MI prototype conflates characteristics of psychopathy and psychosis to represent a malevolent, detached, unpredictably violent offender (see Table 3).– Resembles the most pervasive, if highly unlikely, media stereotype of the mentally

ill: the psychotic psychopath.– Like early proponents of MI, jurors with MI prototypes may believe that these

people have moral defects that render them less responsible for their actions.• Only 21% of jurors had “Mental State-Centered” (MSC) prototypes. Most were male

(71%) and highly educated. The MSC prototype specifically emphasizes impairments in mental state at the time of the offense that are supported by expert evidence (see Table 4). – Shares most (70%) of its characteristics with other prototypes, but emphasizes them

more exclusively (see Table 1)– May be held by the minority of laypeople who believe that it is fundamentally

wrong to punish the insane.– Reflects a broad historical interpretation of mens rea.

Table 1 Overlappinga Characteristics Across Prototype Groups

Table 2Discriminatinga Characteristics of the

Severe Mental Disability Prototype

Table 3Discriminatinga Characteristics of the

Moral Insanity Prototype

Table 4Discriminatinga Characteristics of the

Mental State-Centered Prototype

Exploring Differences Among Prototype Groups in Case Judgments

• Does it matter whether a juror expects a wild beast, a psychopath, or just plain mental state impairments?

• To determine this, jurors read an insanity case vignette, rated their perception of the defendant, and issued a scaled verdict.

• The 3 groups differed on the combined case construal and scaled verdict variable. F (6, 246) = 2.08, p<.01, =.23.

• The Mental State-Centered group perceived the defendant as more mentally disordered, less capable of controlling his beliefs, and less worthy of punishment than the other groups (Fig. 2)

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Figure 2. Group Differ-ences in Case Perception

• The Mental State-Centered group was more likely than other groups to deem the defendant not guilty by reason of insanity (Fig. 3; trend only with MI)

• These differences make sense. The vignette emphasizes the defendant’s delusions and their relationship to his crime. It does not portray the defendant as severely disabled nor psychopathic. The defendant depicted best matches the circumscribed essence of the Mental State-Centered prototype.

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Scaled Verdict

SMD MI MSC

Figure 3. Group Differences in Scaled Verdict (likelihood of finding the defendant insane)

CONCLUSIONS & IMPLICATIONSSummary of Findings

1. Jurors have complex, multifaceted prototypes of insanity that cannot be reduced to legal definitions or psychiatric constructs.

2. Although these prototypes vary markedly across individuals, there are three discernible subgroups of jurors with prototypes that emphasize (1) extreme mental disability, (2) a lay conception of moral insanity, and (3) characteristics more specifically related to mental state at the time of the offense.

3. Prototypes affect the way in which jurors construe case information and render verdicts.

Implications

• Typical defendant may face a jury with conceptions that render them unlikely to deem him insane. Less than 25% of jurors have prototypes focused on legally relevant mental state impairments.

• The law should arguably “curb and correct” prototypes that are conviction prone (Finkel, 1997). Speculative guidelines to aid experts and attorneys in doing so are presented below.

–Jury selection

Voir dire may be used to identify and exclude biased jurors. Carefully explore a prospective juror’s conception of the typical insane person. Assess for the key features of the Severe Mental Disability and Moral Insanity prototypes highlighted in Tables 2-3. The presence of these features may predict jurors’ tendencies to set a “high hurdle” for issuing a verdict of insanity. –Presentation of expert evidence•When presenting expert evidence on a defendant’s mental state, experts and attorneys may maximize their effectiveness by targeting the key features of predominant lay conceptions of insanity that predict verdicts. Past research suggests that legal tests of insanity make little difference to jurors.

•In specific, if the case fits predominant prototype dimensions, focus on (1) characteristics of the SMD or “wild beast,” which are likely to be well-represented in the jury (Table 2), and (2) the overlapping characteristics that are important to all three conceptions of insanity (Table 1). A jury may be more apt to deem a defendant insane as he is shown to exhibit more of the features that most jurors’ conceptions of insanity share.

•If the case does not fit these dimensions, directly target key prototype dimensions in an attempt to modify them. Smith (1993) found that crime prototypes could be brought into greater accord with legal definitions, but only when they were specifically identified and revised. Reasoning by analogy, one might attempt a similar strategy in insanity defense cases. Experts could focus on the discrepancies between jurors’ prototypes and case-specific facts when viewed through the lens of expert knowledge (see paper for details).

STUDY LIMITATIONS• Although the 3-cluster solution in this study was replicable across

sub-samples and methods, and was validated on external variables, it must be replicated with an independent sample. This process is currently underway.

• This research was designed to lay the groundwork for testing the “prototypicality” of jurors’ conceptions of insanity. Future research that uses more realistic trial materials is needed to determine (a) the extent to which jurors render verdicts based on a prototype matching process, (b) the competitive effects of prototypes and legal definitions of insanity, and (c) the extent to which reliance on prejudicial prototypes can be reduced.