how jurors will respond to these variations and if they
are able to distinguish among them. The standards that
jurors are supposed to use in any specific insanity
defense case are delivered to the jurors via jury instruc-
tions. Research has investigated jurors’ responses to
these various standards as presented in jury instructions.
This research has shown that jury decision making is not
substantially affected by the standard that is used or by
variations in jury instructions. Additionally, jurors who
are given instructions and those who are given no
instructions do not seem to significantly differ in their
decisions. Whether a standard is present and, if so,
which type of standard is used appears to have little
effect on jurors’ ultimate decisions, even though the
standards are based on very different legal notions. This
should not be interpreted to mean that jurors do not take
the instructions into consideration when they are delib-
erating, nor does it indicate that they do not take their
duties seriously. Some scholars suggest that jurors inter-
pret insanity cases based on their commonsense under-
standing of mental illness and of the defense itself. It is
argued by Norman Finkel (1988) and others that jurors
may not distinguish among the varying standards
because they rely on their own interpretation of insanity
when judging the appropriateness of the defense.
If jurors are basing their decisions in insanity cases
in part on their commonsense understanding of the
defense, it is important to determine what this com-
monsense understanding might be. Michael Perlin has
written extensively about the common misunderstand-
ings that might be relied on in decision making in
insanity cases. He identified eight “myths” that drive
public perceptions of the insanity defense. These
myths include the belief that the insanity defense is
overused, defendants who plead insanity are usually
faking, the insanity defense is used almost exclusively
in cases that involve violent crimes, pleading not
guilty by reason of insanity (NGRI) is a strategy used
by criminal defense attorneys to get their clients
acquitted, there is no risk to the defendant who pleads
insanity, trials involving an NGRI defense almost
always feature “battles of the experts,” NGRI acquit-
tees spend much less time in custody than do defen-
dants convicted of the same offense, and NGRI
acquittees are quickly released from custody. Perlin’s
myths are examples of the flawed knowledge about
insanity that exists in the public domain. Each of these
myths has been refuted by empirical findings from
multiple sources. However, this misinformation has
the potential to negatively influence jurors’ considera-
tion of the insanity defense in specific cases.In addition to the faulty knowledge that prospective
jurors might have, jurors may also have preexisting
attitudes about the insanity defense that could affect
their decision making. Surveys as well as experimen-
tal studies have revealed that people hold strong neg-
ative attitudes toward this defense. Many prospective
jurors report viewing the insanity defense as a loop-
hole in the legal system through which dangerous
mentally ill people could reenter society or by which
truly guilty criminals who were not mentally ill could
be acquitted. In addition, people perceive the insanity
defense as one that is too frequently used as well as
abused. Research also indicates that negative attitudes
about mental illness are largely fueled by this misin-
formation about mental illness. For example, people
have a tendency to overestimate the number of defen-
dants who plead insanity and who are acquitted by
reason of insanity, while they tend to underestimate
the period of confinement for insanity acquittees. The
relationship between insanity knowledge and attitudes
is such that more accurate knowledge is related to
more favorable attitudes.
Negative attitudes have been shown to decrease
jurors’ willingness to consider and to render NGRI
verdicts. Research indicates that attitudes toward
mental illness and the insanity defense exert signifi-
cant influence on mock jurors’ verdicts in insanity
cases, even more so than the case facts. Jurors with
negative attitudes are far less likely to render NGRI
verdicts. Attitudes toward the death penalty are also
related to decision making in insanity cases. Jurors
with positive attitudes toward the death penalty are
crime-control oriented, tend to hold negative attitudes
toward the insanity defense, and are significantly less
willing to render NGRI verdicts.
Another focus of research on the origins of potential
jurors’ beliefs about the insanity defense has been in the
study of insanity prototypes, or the concept of the typi-
cal insanity defendant. In several prototype studies,
researchers have found that jurors’ notions of insanity
included extreme impairments at the time of the offense
as well as extreme psychosis. They tended to inflate
symptoms of psychosis, as well as portray the offender
as extremely violent. These prototypes could produce
expectations about defendants in insanity trials that
could in turn affect decision making, although there has
been little research on this phenomenon.
Once a trial in which insanity is claimed begins, it
is the responsibility of the jurors to assess the evi-
dence presented to them and the viability of the insan-
ity defense in that case. Research has investigated theInsanity Defense, Juries and——— 371I-Cutler (Encyc)-45463.qxd 11/18/2007 12:43 PM Page 371