Daniel A Martell. Law and Human Behavior. Volume 16, Issue 3, June 1992.
This article examines the evidentiary value of forensic neuropsychological testimony to inform judicial decision making in the context of the criminal law. Forensic neuropsychology, broadly defined, involves the application of clinical neuropsychological assessment to legal issues (Gilandas & Touyz, 1983; Golden & Strider, 1986; McMahon, 1983). To date, its role has evolved almost exclusively in the realm of the civil law, given its relevance to issues in disability determination, workman’s compensation, and personal injury cases (Anchor et al., 1985; Mack, 1980). This emphasis on civil law is reflected in the literature introducing lawyers to the potential contributions of neuropsychologists (Anchor, Rogers, Solomon, Barth, & Peacock, 1983; Incagnoli, 1985; Pierce, 1985; Whelihan & Ivans, 1981), as well as literature directed at neuropsychologists to outline their participation in the legal arena (Bigler, 1986; Gilandas & Touyz, 1982; Golden & Strider, 1986; Kurlychek, 1984). Consequently, there is very little scholarship regarding potential applications of neuropsychology to issues in the criminal law.
What little treatment there is of criminal-legal issues in the literature on forensic neuropsychology has been superficial. A few sources acknowledge the potential relevance of neuropsychology to issues in criminal law, but either do not pursue those issues in detail (e.g., Gilandas & Touyz, 1983; Golden & Strider, 1986), or dismiss them as too infrequent to warrant serious attention (McMahon & Satz, 1981). Only three references touch on criminal-legal neuropsychology in any greater detail. Anchor et al. (1985) comment briefly on neuropsychological evaluations in competency to stand trial and criminal responsibility determinations; Hall and McNinch (1988) begin to examine the role of frontal lobe impairment as it relates to issues of criminal responsibility; and a chapter by Schuster (1989) includes two criminal case examples.
The present article provides a closer examination of this largely unexplored area by considering forensic neuropsychology as it relates to issues arising in the criminal law. After examining components essential to competent forensic neuropsychological assessment, this article will focus on the application of neuropsychological evidence to specific psycholegal issues in the criminal process. These will include evaluation of (a) competency to stand trial, particularly in the evaluation of potential for restoration of fitness to proceed (pursuant to Jackson v. Indiana, 1972); (b) criminal responsibility, diminished capacities, and the insanity defense; and (c) related competencies specific to the criminal process. Examples of neurobehavioral disorders are used to illustrate their implications for these issues. Finally, empirical and ethical issues relating to the admissibility of neuropsychological evidence are presented.
Why Neuropsychology?
Advances in clinical neuroimaging and emerging evidence of significant levels of brain dysfunction in forensic populations foreshadow a larger role for the neurobehavioral sciences in the criminal law (Martell, 1992; Tancredi & Volkow, 1988). Clinical neuropsychology, but virtue of its unique ability to characterize the objective psychological, behavioral, and emotional consequences of abnormal brain conditions, has the potential to play an increasingly important role in the criminal courtroom.
Traditionally, clinical psychology and the law have come together around issues of major mental illness: Does the defendant suffer from a mental “disease” or “defect,” and if so, what is its impact on his or her behavior relevant to the requirements of the law? In this context, concern has centered almost exclusively on psychosis, as the expense of other potentially relevant sequelae of brain dysfunction. Many neuropsychological disorders raise largely unexplored issues that diverge from the traditional concern with psychosis, yet have important implications for criminal-legal standards of behavior. Most of these disorders fall clearly within the scope of “mental disease or defect” language. For example, they encompass mental “disease” when we consider neoplastic disease (brain tumors), cerebrovascular disease, or progressive degenerative dementias (e.g., Alzheimer’s disease, AIDS-Dementia Complex). Similarly, they encompass “defect” in the form of acquired head injuries, perinatal brain abnormalities, neurodevelopmental anomalies, and mental retardation. Such “organic” brain disorders may or may not result in psychosis, yet many result in memory, language, cognitive, and/or behavioral impairments with significant implications for criminal-legal standards of behavior. Among neurobehavioral scientists, neuropsychologists routinely address the cognitive, behavioral, and emotional sequelae of brain damage or cerebral dysfunction at a level adequate to inform judicial decisions in the presence of organic brain disease or defect.
Simultaneously, the distinction between “organic” and “functional” mental disorders is no longer so clear. Recent tomographic studies (reviewed by Raz & Raz, 1990) document the presence of structural brain abnormalities in those major psychotic disorders most often associated with incompetency and/or insanity in the criminal law (i.e., schizophrenia and affective psychoses). This kind of evidence is becoming so pervasive that Spitzer, Williams, First, and Kendler (1990) have proposed eliminating the term organic from the DSM-IV altogether, to reflect the view that all mental illness may have some basis in brain abnormality. Consequently, the growing behavioral science concern with brain status and mental disorder is likely to be reflected in the increasing introduction of neuroscientific evidence in criminal proceedings (Tancredi & Volkow, 1988).
Neuropsychological Evidence
The particular appeal of neuropsychological evidence in the criminal context is the expert’s ability to bring quantified, normative data on brain-behavior relationships to bear in support of what have traditionally been professional opinions based on mental status examinations and clinical interview techniques. While psychological data about mental functioning are not the exclusive domain of the neuropsychologist, neuropsychological assessment generally addresses brain-behavior relationships in greater depth and with greater behavioral specificity than other areas of psychology. The ability to provide the trier of fact with a normative description of a defendant’s neurobehavioral strengths and weaknesses can bring important new information to the criminal decision-making process.
Equally relevant to criminal law issues is the ability of neuropsychological assessment to relate the presence of structural and functional brain abnormalities to changes in individual behavior (Boll, 1985; Heaton & Pendleton, 1981; Jarvis & Barth, 1984). In the criminal context it is not enough simply to show that the defendant has a brain lesion, just as the de facto presence of a major mental illness alone does not render a defendant incompetent or insane. Rather, the behavioral consequences of the lesion are central to the concerns of the law. In this regard, neuropsychology enjoys a distinct advantage over traditional medical testimony regarding evidence of brain damage. While emerging neuroimaging technologies such as Computerized Axial Tomography (CAT), Positron Emission Tomography (PET), and Magnetic Resonance Imaging (MRI) permit very specific evidence regarding the presence and nature of brain lesions, they reveal little or nothing of the behavioral consequences of the lesion in terms of level of impairment across cognitive, emotional, and behavioral spheres (Boll, 1985). Most medical opinions, beyond verifying the presence and location of the lesion, ultimately resort to informed speculation when it comes to relating the lesion to the behavior of the defendant in a specific case. This is why a referral for neuropsychological assessment is often made in clinical settings, and why it is relevant to criminal law: neuropsychology assesses the impact of a brain lesion on behavior and mental functioning.
Studies have documented the sensitivity of neuropsychological assessment to detect subtle abnormalities in brain function that may go undetected even by the most sophisticated medical/neurological techniques (Barth, Gideon, Sciara, Hulsey, & Anchor, 1986). Neuropsychological test batteries have been shown to be equivalent or superior to traditional neurodiagnostic techniques (including physical neurological examination, EEG, pneumoencephalography, angiogram, x-ray, and CAT scan) in detecting both the presence and general location of brain damage (Boll, 1978; Filskov & Goldstein, 1974; Tsushima & Wedding, 1979). This capability to reliably detect brain abnormality is important to establishing the presence of “mental disease or defect.” However, clinical neuropsychology’s greater strength lies in its descriptive ability to correlate evidence of brain abnormality with behavioral changes and outcomes with implications for the subject’s everyday level of functioning (Heaton & Pendleton, 1981). Its sensitivity for detection and behavioral description make neuropsychological assessment especially useful when used to amplify or clarify findings from medical/neurological techniques, documenting the consequences of brain lesions for the individual’s levels of functioning.
The capability to relate a known brain lesion to the capacities of a defendant relevant to several legal standards of behavior sets clinical neuropsychology apart from medical/neurological testimony, and ultimately makes it of direct relevance to the issues facing the trier of fact. While research advances (especially in the application of neuropsychological data to forensic issues) will help the field to fully realize this potential, the argument can already be made that the current state of the art permits valid opinions to be offered that are immediately relevant to criminal/forensic issues. Even Ziskin and Faust (1988), who have been criticized for their one-sided portrayal of the inadequacies of psychiatric and psychological testimony (cf. Brodsky, 1989; Matarazzo, 1990), endorse neuropsychology as an area with potential to inform legal decision making. Despite reservations regarding the state of the art as it stood in the mid-1980s, they assert, “Overall, in our opinion, the field of neuropsychology shows substantial promise, and the quality of research and method are often a cut above that seen in many other areas of clinical psychology and psychiatry” (p. 784).
However, this remains an important area for future research. Good studies on which to base opinions about the relationship between neuropsychological test performance and activities of daily life are few (Boll, 1985; Heaton & Pendelton, 1981). The need for greater ecological validity is one of the major challenges currently facing the field (Franzen, 1989; Heinrichs, 1990), and this is especially true for criminal/forensic applications of neuropsychology (see Konecni & Ebbeson, 1979). While mainstream neuropsychological research has been investigating relationships between test scores and activities of daily living and work performance (cf. Butler, Anderson, Furst, Namerow, & Satz, 1989; Heaton & Pendelton, 1981; Matarazzo, 1972), more attention needs to be paid to their relationship with criminal-legal standards of behavior.
Forensic Neuropsychological Assessment
Clinical neuropsychology, the study of brain-behavior relationships, is relatively new as a unique area of psychological inquiry, although research in the area has been ongoing since the 1940s (Lezak, 1983). It is currently one of the most rapidly developing subareas of psychology. It is also a field in which much research remains to be done. This is especially true with regard to the forensic applications of neuropsychology.
The very best neuropsychological assessments represent the highest level of contemporary objective psychological evaluation. A variety of mechanical, observational, and paper and pencil tests are generally employed to assess brain integrity and to describe behavioral strengths and weaknesses associated with pathological brain conditions. Integrating data from tests of specific neurobehavioral abilities with those from achievement, intelligence, and personality measures, the neuropsychologist can arrive at a fairly comprehensive picture of an individual’s level of cognitive, emotional, and behavioral functioning. These data are then evaluated in the context of the subject’s history (education, employment, highest level of “premorbid” functioning), previous testing, and medical findings (e.g., results of neurological examination, brain scans, etc.) to assess the nature and extent of brain-behavior strengths and weaknesses.
Brain damage is not a unitary construct; there are many forms of brain damage that may arise from very different causes. Hence no single test is adequate for the detection or diagnosis of brain damage (Boll, 1978, Jarvis & Barth, 1984). Typical neuropsychological evaluations include a comprehensive battery of assessment techniques. The Halstead-Reitan Neuropsychological Battery (HRNB: Boll, 1981; Reitan & Wolfson, 1985) and the Luria-Nebraska Neuropsychological Battery (LNNB: Golden, 1981) are the most prominent standardized techniques. Boll (1978, 1985) and Golden (1986) present detailed accounts of the research data supporting the reliability and validity of the Halstead-Reitan and Luria batteries, respectively. Kane, Parsons, and Goldstein (1985) have demonstrated the comparability of these two test batteries with regard to diagnostic screening accuracy, and evaluation of the level of impairment.
There are also a number of specialized tests for specific neuropsychological functions, many described in detail by Lezak (1983) and Spreen and Strauss (1991), that may be used in conjunction with one of the aforementioned batteries, or combined independently to form a unique battery. This latter technique, sometimes referred to as the process/qualitative (Kaplan, 1990) or hypothesis-testing approach to neuropsychological assessment, tailors an ideographic battery of selected tests to the demands of an individual case.
Regardless of the battery of tests selected, functional areas of interest central to all neuropsychological assessments generally include (a) intelligence, (b) attention and orientation, (c) sensory-perceptual functioning, (d) pure motor functioning and control, (e) visual-motor integration, (f) learning and memory (verbal and visual, immediate, short term, and long term), (g) language functioning, and (h) higher integrative cognitive functions including the executive control (i.e., planning and organization) of behavior, abstract reasoning, and problem-solving. Neuropsychologists also routinely assess educational achievement and personality functioning. Principles of neuropsychological assessment are discussed in much greater detail by Lezak (1983).
The practice of forensic neuropsychology demands the highest standards of thoroughness, accuracy, and care in the administration, scoring, interpretation, and reporting of findings. The general comparability of the available test batteries (Kane et al., 1985) makes the choice of a battery less important than meticulous attention to norms. Often, the forensic issue may require additional testing beyond a standard battery to more thoroughly address the psycholegal issues or to more completely describe the defendant’s strengths or disabilities. Supplementation of the standard battery is common in clinical practice (Jarvis & Barth, 1984), and should be encouraged in forensic neuropsychological assessment. However, it is extremely important that the clinician select supplemental tests with well-documented norms, adjusted where appropriate for age and education, and potential racial, ethnic, or cultural bias (Bernard, 1989; Franzen, 1989; Heaton, Grant, & Matthews, 1991; Leckliter & Matarazzo, 1989; Matarazzo, 1990; Spreen & Strauss, 1991). Only then can it speak adequately to the presence or absence of mental disease or defect, and its relationship to specific criminal-legal referral issues.
An increasingly important area of neuropsychological evaluation (with direct relevance to forensic applications) is the assessment of attempts to malinger, simulate, or exaggerate brain dysfunction. However, this is a controversial area within neuropsychology because of limitations in study designs and the interpretation of research findings. Studies of the ability of neuropsychologists to detect malingering have fallen on both sides. Faust, Hart, Guilmette, and Arkes (1988) have questioned the ability of neuropsychologists to detect adolescents told to malinger neuropsychological deficits. However, Bigler (1990) notes several problems with the design of the Faust study that cast serious doubt on the validity of their findings. Other studies using adult populations have affirmed the ability of neuropsychologists to discriminate between true and malingered test performance above chance levels, including studies using data from the Halstead-Reitan (Goebel, 1983; Heaton, Smith, Lehman, & Vogt, 1978) and Luria-Nebraska (Mench, 1984) neuropsychological test batteries. However, there are also arguments over the methodological strengths and weaknesses of these studies (cf. Faust et al., 1988; Guilmette & Giuliano, 1991; Pankratz, 1988).
One of the major methodological problems with the literature on neuropsychology and malingering is that none of the studies have incorporated specialized tests that have been developed to help detect efforts to simulate neuropsychological impairments (Binder & Pankratz, 1987; Lezak, 1983; Pankratz, 1988; Wasyliw & Cavanaugh, 1989). Rather, they generally have relied on standard test scores alone, often in the absence of adequate background information regarding the referral issue or presenting problem. A number of these specialized clinical techniques have been developed, and are advocated for forensic use. It is critical that any forensic neuropsychological evaluation include as many of these specialized techniques as possible. Although the definitive study has yet to be conducted, there is evidence for the utility of each of these techniques (Lezak, 1983; Pankratz, 1988). When considered in the context of an individual’s performance on a standard battery, these techniques may significantly increase the ability to detect simulators. Even lacking a definitive research study, neuropsychological testimony will be more credible if the clinician has clearly taken this issue into account and incorporated these techniques to assess it.
Relating Neuropsychological Impairment to Legally Relevant Behavior: Base Rates and Research Findings
The ecological validity of neuropsychological evidence is enhanced if it can be shown that brain impairment is associated with behaviors relevant to criminal law. In this regard, it is useful to consider (a) the ways in which neuropsychological impairment interferes with the defendant’s ability to participate in various criminal procedures (i.e., criminal competencies); and (b) ways in which it contributes to the causation of criminal behavior (which goes to issues of criminal responsibility). This section begins with a review of research on the prevalence of neuropsychological disorders in criminal and forensic populations. Because brain damage can have significant implications for both criminal competencies and criminal behavior, knowledge of the prevalence of brain dysfunction provides an estimate of the scope of the problem. Then, studies that associate neuropsychological impairment with violence and criminal behavior will be reviewed.
Base Rates of Brain Impairment in Forensic Populations
The lack of base rates for neuropsychological disorders is a significant problem across all clinical settings (Duncan & Snow, 1987), and this is particularly true in forensic settings. However, recent epidemiological studies are beginning to provide estimates of the prevalence of abnormal brain conditions in various forensic populations.
Clues to the prevalence of brain disorders among mentally disordered offenders come from three diagnostic census studies. Odejide (1981) studied “criminal lunatics” at the Lantoro Psychiatric Institution in Nigeria. His data show that 24.6% of the subjects were either epileptic (18.9%) or suffered from organic psychoses (5.7%). Häfner and Böker (1982) conducted an epidemiological diagnostic study of 533 mentally disordered offenders entering the forensic mental health system in the Federal Republic of Germany over a 10-year period. Their data suggest that 33.6% of these patients had a diagnosis reflecting organic cerebral impairment. These included mental retardation (12.7%), late-acquired brain damage (8%), cerebral atrophy (7.5%), and epilepsy (5.4%).
Martell (1992) presents data from 50 randomly selected American forensic patients retained in a maximum-security state hospital for mentally disordered offenders in New York. Multiple indicators of potential brain dysfunction were present in 66% of these cases, with at least one indicator present in 84% of the subjects. The presence of certain brain disorders was significantly associated with indictments for violent crimes in this sample. Specific findings included a history of severe head injury with loss of consciousness (22%), seizure activity (8%), evidence of cognitive impairment (18%), abnormal neurological findings (75%), and abnormal neuropsychological or neurodiagnostic findings (32%).
Other studies have examined brain impairment in jail and prison populations (Monroe, 1981). Neighbors (1987) conducted a psychiatric epidemiologic study of 1000 prisoners randomly selected from the total prison population in the state of Michigan. Both the Diagnostic Interview Schedule (DIS) and the Structured Clinical Interview for DSM-III-R (SCID) were used to establish lifetime prevalence (DIS) and current primary diagnosis (SCID). His data suggest that 8.2% of the prison population meet research diagnostic criteria for organic brain disorders (5.3% with Organic Brain Syndrome/Cognitive Impairment and 2.9% with Organic Personality Disorder—Explosive type). However, structured diagnostic interviews are not terribly sensitive instruments for the detection or diagnosis of abnormal brain functioning, hence these findings probably underestimate the extent of brain dysfunction in the population.
Studies using neuropsychological test batteries suggest much higher levels of brain impairment. Yeudall and From-Auch (1979) document varying patterns of abnormal HRNB findings in numerous forensic populations, including adolescent delinquents, forensic psychiatric patients, aggressive psychopaths, sex offenders, and violent criminals. Among adult criminals, Yeudall (1977) reports abnormal HRNB findings in 90% of his sample, including 100% of rapists, 94% of homicide offenders, and 87% of assaultists. Lewis and her colleagues conducted uncontrolled, descriptive studies of both juvenile and adult prisoners on death row (Lewis et al., 1988; Lewis, Pincus, Feldman, Jackson, & Bard, 1986). These studies documented significant brain dysfunction in the majority of these subjects, including neuropsychological impairment on the HRNB, histories of head injury, neurological impairment, and cognitive deficits. If confirmed in controlled studies, these findings would have important implications for issues of competency to be executed, as well as ways in which biological bases of violent behavior will be viewed in the criminal justice system in coming years.
Neuropsychological Impairment and Violent Crime
Brain damage can impact the entire range of human behavior. However, its relationship to criminal behavior often springs from some combination of disinhibition, impaired social judgment, hypersexuality, aggression, and/or violence. Of these, research linking brain dysfunction to aggression and violence is perhaps the most developed relative to criminal-legal standards of behavior (Volavka, Martell, & Convit, 1992).
Theoretical models emerging from neuropsychology (Gorenstein & Newman, 1980; Yeudall, Fedora, & Fromm, 1987) and neurology (Tancredi & Volkow, 1988; Weiger & Bear, 1988) suggest that brain damage increases the risk of violent behavior. Abnormal brain functioning may impair inhibition of violent impulses, and/or stimulate excesses in impulsivity and behavioral dyscontrol. Either mechanism may increase an individual’s propensity to aggressive or violent behavior, particularly in combination with other characterological, environmental, or situational risk factors. Researchers have begun to document the importance of several specific types of brain impairment in violent behavior, including head injury, mental retardation, frontal and temporal lobe dysfunction, seizure disorder, and neurological abnormalities (cf. Langevin, Ben-Aron, Wortzman, Dickey, & Handy, 1987; Martell, 1992; Nachshon & Denno, 1987; Silver & Yudofsky, 1987).
Neuropsychological studies of brain function in violent groups have yielded significant support for theories that associate violent behavior with brain dysfunction (Pontius & Yudowitz 1980; Spellacy, 1977, 1978; West, 1981). For example, Bryant, Scott, Golden, and Tori (1984) found a significant relationship between learning disability, neuropsychological deficits, and violent criminal behavior. Impaired scores on subscales of the Wechsler Adult Intelligence Scale have also been associated with violent behavior (Dieker, 1973; Kunce, Ryan, & Eckelman, 1976). Programmatic studies by Yeudall and his colleagues (Yeudall & Fromm-Auch, 1979) have documented significant neuropsychological deficits in both violent prisoners and forensic psychiatric patients.
Other neuropsychologists have also demonstrated the ability of neuropsychological findings to discriminate between violent and nonviolent offenders (Spellacy, 1978; West, 1981). Patterns of impairment on the HRNB consistently discriminate juvenile delinquents from matched controls (Berman & Siegal, 1976; Spellacy, 1977; Yeudall, From-Auch, & Davies, 1982). Studies using the HRNB have also reported significant differences in the neurospychological performance of psychopathic and nonpsychopathic criminals (Fedora & Fedora, 1983), suggesting greater impairment of dominant (left) hemisphere function among criminal psychopaths (see also Hare & McPherson, 1984; Jutai & Hare, 1983). Langevin et al. (1987) used both the LNNB and the HRNB in a study comparing murderers, other violent offenders, and nonviolent controls. They found that while the LNNB did not discriminate among these groups, the HRNB did detect significant differences, with killers and assaulters showing greater levels of impairment than controls on several of the subtests. Taken together, this literature suggests that neuropsychological impairment may play a significant role in the criminal behavior of certain offenders. However, the nature and extent of this role, and its interaction with other personal environmental and situational risk factors remains to be determined.
Neuropsychological Evidence in the Criminal Context
A significant controversy exists over the propriety of behavioral science experts providing opinions that address directly the ultimate issue before the court in criminal matters (Rogers & Ewing, 1989). The value of neuropsychological evidence lies in its ability to provide the trier-of-fact with objective data that illuminates the substantive questions that underlie the ultimate issues. Hence, proper neuropsychological testimony should not address ultimate legal issues directly.
In discussing the “ultimate issue issue,” Slobogin (1989) makes the distinction between penultimate language—words reflecting the substance of the legal test—and the ultimate issues themselves. Ultimate issues of insanity and incompetency are uniquely legal concepts whose ultimate determination properly lies with the trier-of-fact. However, Slobogin argues that expert evidence that clarifies the legal language underlying the ultimate issues is the proper domain of the behavioral science expert. “Legal tests often contain language that is meaningful to mental health professional in the expert role. My view, contrary to the ABA’s, is that so long as a term has clinical content, the fact that it has been given specific legal meaning should not prevent it from being used by the clinician” (Slobogin, 1990, p. 263). Emphasis should be placed on providing the court with data that go directly to the penultimate language, and help to inform the court in its deliberations regarding the ultimate issues at hand. Assuming Slobogin’s philosophical position, the following section of this article will explore some of the legal language that sets the stage for expert neuropsychological evidence.
Competency to Stand Trial
The behavioral standards underlying findings of competency to stand trial spring primarily from the legal language of two cases: Dusky v. United States (1960) and Weiter v. Settle (1961). Dusky states:
It is not enough for the district judge to find that the “defendant [is] oriented to time and place and [has] some recollection of events,”…the “test must be whether he has sufficient present ability to consult with his lawyer with a reasonable degree of rational understanding—and whether he has a rational as well as factual understanding of the proceedings against him.” (p. 402, quoting United States Solicitor General Rankin)
The tests set out in Dusky are further elaborated in Weiter, which requires that the defendant’s “elementary mental processes [be] such that he apprehends (ie., seizes and grasps with what mind he has) that he is in a Court of Justice, charged with a criminal offense,” and that he be cognizant of the significant legal actors and their roles in the proceedings (i.e., the judge, prosecutor, defense attorney, jury, etc). Both of these cases set forth standards that require a defendant to be oriented to the world around him or her (i.e., that he or she have the “mental capacity to appreciate his presence in relation to time, place, and things”), and have “memory sufficient to relate [the facts surrounding him at the time of the offense at the time and place where the law violation is alleged to have been committed] in his own personal manner” ( Weiter, 1961, pp. 321–322).
These cases establish a two-pronged test of competency: The defendant must meet the requirements of a cognitive prong, and an interpersonal/behavioral cooperation prong. The cognitive prong is encompassed in legal language concerning (a) orientation, (b) understanding or “apprehension,” (c) memory, and (d) at least a rudimentary synthesis of the charges, the court principals, potential pleas, and outcomes. These cognitive requirements are striking in their similarity to the mental functions assessed in a standard neuropsychological evaluation. The mental abilities required by the cognitive prong reflect the direct relevance of neuropsychological evidence. A wide range of brain disorders can impair a defendant’s abilities relevant to these standards, including mental retardation (Travin, Klein, & Protter, 1985), various forms of dementia, amnesia and memory impairments, and frontal lobe dysfunction.
The interpersonal/behavioral cooperation prong involves the defendant’s ability to communicate effectively with an attorney, and to participate effectively in his or her own defense. The Dusky test begins by requiring that the defendant have “sufficient present ability” to cooperate with counsel. Establishing the level of functioning that constitutes sufficient present ability in a given case is ultimately a judicial determination. However, neuropsychological testimony can and should provide objective data to help establish whether a given defendant’s present abilities are legally sufficient. This entails assessment of the defendant’s ability to comprehend an attorney’s instructions or advice, and to make reasoned decisions based on that advice. It also involves assessing the ability to collaborate effectively in developing and pursuing a defense, for example, the ability to attend to the testimony of witnesses and inform the attorney of discrepancies or concerns. Many forms of brain damage can interfere with these abilities. For example, disorders of language known as aphasias can significantly interfere with a defendant’s ability either to comprehend spoken language (receptive aphasia) or to communicate effectively through language (expressive aphasia). Similarly, disorders of attention, concentration, and memory may impair a defendants ability to attend to and follow events in the trial over several days.
Literature on the applied psychological evaluation of competency to stand trial (e.g., Grisso, 1986; Melton, Petrila, Poythress, & Slobogin, 1987; Roesch & Golding, 1987) has not addressed its neuropsychological assessment in any depth. However, neuropsychological evidence regarding competency is relevant in at least two primary areas: (a) determinations of the defendant’s present ability to proceed in court; and (b) after a determination of incompetency, in the assessment of the defendant’s potential for restoration of fitness to proceed pursuant to Jack son v. Indiana (1972). In many cases, determinations of present competency to stand trial would benefit from neuropsychological assessment. This is particularly true in cases where the reason for a defendant’s apparent incompetency is unclear. For example, referral for forensic neuropsychological evaluation could be indicated when mental status examination suggests memory impairment, attentional deficits, mental retardation, some other organic basis for the defendant’s incompetency, or malingering.
However, the role for forensic neuropsychology is likely to become even more important after a finding of incompetency. The Supreme Court’s landmark decision in Jackson v. Indiana (1972) created a largely unexplored territory for forensic evaluations in competency determination. In Jackson, the Court held, in part, that
a defendant cannot be held more than the reasonable period of time necessary to determine whether there is a substantial probability that he will attain competency in the foreseeable future. If it is determined that he will not, the State must either institute civil proceedings applicable to indefinite commitment of those not charged with a crime, or release the defendant. (p. 406)
This decision places a burden squarely on forensic clinicians to actively evaluate an incompetent defendant’s potential for restoration to competency. Jackson thus provides what may become the greatest single opportunity for neuropsychology to play a unique and critical informative role in competency proceedings.
Martell and Sanders (1991) present the first clinical data on this class of defendants in the 20 years since the Jackson decision. They report on all cases converted to civil status pursuant to Jackson from a maximum-security hospital in New York City over a five year period. Of these, 70% had documented evidence of neuropsychological brain abnormality. Specific disorders included AIDS-dementia, Pick’s disease, Alzheimer’s disease, mental retardation, and alcoholic dementia.
In such cases, the neuropsychologist can establish a defendant’s current level of functioning, relate it to available history and baseline data, and perform serial testing to document any significant change in the neuropsychological status of the defendant over time. It also may be important in cases where it is unclear why a defendant is not responding to treatment. For example, many forensic psychiatric patients with organic disorders are misdiagnosed with major psychotic disorders (e.g., schizophrenia; Martell, 1992). In some cases, treatment with antipsychotic medications may actually exacerbate the symptom presentation in these patients (Hales & Yudofsky, 1987). Careful neuropsychological assessment would help to clarify the diagnostic picture, as well as offering suggestions for alternative treatments.
Criminal Responsibility, Diminished Capacities, and the Insanity Defense
The forensic neuropsychological issues in this area are less clear cut than those of competency to stand trial, and the role for neuropsychology is arguably more controversial. However, there may be an increasingly viable role for neuropsychology here. Brain damage is coming to be viewed as a potential risk factor for violent behavior in conjunction with other personal, environmental, and situational risk factors (Martell, 1992).
Recent advances in neuroscience, driven largely by the advent of new imaging technologies for the study of brain structure and function, are raising important new issues in the criminal law. Increasingly, data from these new technologies are being introduced as dramatic evidence of brain damage in insanity proceedings (e.g., U.S. v. Hinckley, 1982). However, as noted earlier, while neuroimaging technologies can provide powerful evidence of the presence, type, location, size, and angle of brain lesions, they provide the trier of fact with little information about the behavioral sequelae of a given lesion. It is precisely in this area that the neuropsychologist is best prepared to provide evidence to inform the decision-making process. It may prove useful to document the preservation of abilities despite the presence of a known lesion, or alternatively to delineate the extent and quality of disability associated with the lesion.
Historically, two precedents have emerged to regulate insanity determinations in American jurisprudence: the McNaughtan standard, and the American Law Institute (ALI) standard (Model Penal Code, 1962). There is a significant literature that addresses the psychological issues raised by these standards (e.g., Golding & Roesch, 1987; Melton et al., 1987; Monahan & Walker, 1990). The McNaughtan standard states:
To establish a defense on the ground of insanity, it must be clearly proved that, at the time of committing the act, the party accused was laboring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing; or if he did know it, that he did not know what he was doing was wrong. (p. 718)
The language of the McNaughtan standard essentially establishes a largely cognitive test for insanity, being concerned primarily with the extent to which the defendant did or did not know what s/he was doing. In contrast, the ALI language modifies the test for insanity:
A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity either to appreciate the criminality (wrongfulness) of his conduct or to conform his conduct to the requirements of law.
By interjecting the term “appreciate,” the ALI test broadens the cognitive Mc Naughtan standard to encompass affective and emotional factors as well as cognitive factors. From a neuropsychological perspective, “appreciation” implies higher-order cognitive abilities that might range from simple awareness or recognition, to a fairly sophisticated ability to note distinctions or to be conscious of the significance, desirability, or impact of his or her behavior. A number of brain disorders, especially damage to the frontal cortex, can effectively impair the ability to accurately perceive or reflect on one’s own behavior (Hall & McNinch, 1988). For example, disorders known as agnosias result in a deficiency of self-awareness or self-perception (Lezak, 1983) that may impair a defendant’s ability to appreciate the nature and/or consequences of his or her behavior.
Secondly, the ALI standard does not require a defendant’s total lack of appreciation of the nature of his or her conduct, but rather that he or she “lacks substantial capacity.” Determining what is legally “substantial” ultimately falls to the trier-of-fact. However, the neuropsychologist is in a good position to quantify and characterize the degree of impairment exhibited by a defendant, and to aid the fact-finder in determining whether such a level of impairment constitutes a “substantial” lack of capacity. For example, a neuropsychologist might present data showing that the defendant falls three standard deviations below the mean on tests of social judgment and goal-directed behavior. The judge or jury could then use that evidence in determining whether that degree of impairment in those aspects of behavior constitutes a substantial lack of capacity.
Finally, the ALI test adds a “volitional” clause concerning the defendant’s ability (or inability) to control his actions. The volitional clause, however, came under considerable scrutiny in the post-Hinckley era, and while it remains in force in some jurisdictions it was eliminated from the federal standards in 1984 (Mayer & Steadman, 1987).
Constriction of the volitional prong of the ALI test in the post-Hinckley era reflects potentially erroneous assumptions about the impact of mental disease or defect on “volitional” human behavior (Hall & McNinch, 1988; Perlin, 1990; Tancredi & Volkow, 1988). This is consistent with the APA’s position on the insanity defense (American Psychological Association, 1984), which opposed the elimination of the volitional prong until more research data become available to assess its basis in scientific reality. A growing body of research literature has developed linking violence and brain dysfunction (e.g., Langevin, et al., 1987; Silver & Yudofsky, 1987; Volkow & Tancredi, 1987). In addition, a neuropsychology of intent is evolving (Brown, 1987; Goldberg, 1987), implicating frontal lobe defects in the impaired control, planning, and organization of behavior (see Hall & McNinch, 1988). As noted above, frontal lobe syndromes have been clearly associated with violent behavior (Heinrichs, 1989; Kling 1976; Pontius, 1984; Volkow & Tancredi; 1987), and may go directly to the issue of volitional impairment (Gorenstein, 1990; Kendel & Freed, 1989). Similarly, there is a growing literature relating temporal lobe functioning and violence, including controversial studies of temporal lobe epilepsy (Devinsky & Bear, 1984; Furgeson, Rayport, & Corrie, 1986; Monroe, 1986; Stone, 1984), episodic dyscontrol (Rickler, 1982), and temporal lobe lesions secondary to head injury (Wood, 1984).
A related area of criminal responsibility determination with significant potential for forensic neuropsychological input is the evaluation of diminished capacities. Conceptually distinct from insanity determination, a diminished capacities defense attempts to reduce the severity of the charge by challenging the mental element of the prosecution’s prima case (cf. McCord, 1987; Monahan & Walker, 1990). For example, distinctions between murder, manslaughter, and nonnegligent homicide often hinge on whether the prosecution can show that the crime was committed intentionally, knowingly, recklessly, or negligently (Morse, 1984). Unlike the insanity defense, which admits the criminal act but asserts that the defendant had no criminal intent, the diminished capacities defense attempts to show that the defendant was able to form less than the criminal intent required by the charge, and hence should only be convicted of a lesser offense.
McCord (1987) notes that although diminished capacities is distinct from the insanity defense, the psychological evidence presented is often quite similar. Here, forensic neuropsychological evidence could be used to establish the cognitive abilities of the defendant relevant to the legal definitions of the state of mind required to constitute the offense. For example, a defendant with Alzheimer’s disease may lack the ability to organize and plan his or her behavior adequately to form the legal intent required to commit arson, and hence may only be found guilty of a lesser charge such as reckless endangerment.
Other Competencies Arising in the Criminal Process
Neuropsychological evidence also may become increasingly important in a range of other criminal competency issues, including waiver of Miranda rights, competency to confess, competency to make a plea, competency to be sentenced, predictions of dangerousness pursuant to the death penalty, and competency to be executed (cf. Heilbrun & McClaren, 1988; Melton et al., 1987; Perlin, 1987; Small & Otto, 1991). Recent judicial decisions in several of these areas raise important issues of potential neuropsychological relevance.
For example, in the U.S. Supreme Court’s controversial decision in Penry v. Lynaugh (1989), mental retardation alone was found to be insufficient to declare a defendant incompetent to be executed. The court held that the jury must weigh the defendant’s mental status, and the extent to which the mental retardation is so profound or severe as to render the defendant incapable of understanding the punishment and why he or she is to receive it. Here, neuropsychological evidence regarding not only the degree of retardation, but its impact on the defendants comprehension, understanding, and abstract concept formation could be introduced. Similar death penalty cases involving the mentally ill (e.g., Ford v. Wain-wright, 1986) also warrant a consideration of neuropsychological evaluation, especially in light of the prevalence of brain damage attributed to death row inmates by Lewis and her colleagues (Lewis et al., 1986, 1988).
Across many of these areas, neuropsychological evidence may have greatest relevance as it involves the potential extension of the legal theory set out in Jackson v. Indiana regarding whether the defendant will ever be restored to competency. In death penalty cases, for example, a progressive brain disease may prevent a condemned inmate from ever regaining the mental capacity required to meet the test of competency to be executed. Radelet and Barnard (1988) advocate commutation of the death sentence in cases where the defendant is found incompetent. As ethically appealing as this would be for mental health professionals (cf. Bonnie 1990; Brodsky, 1990), it is unlikely to be adopted as a matter of legal policy. However, assessment of potential for restoration to competence for execution would be consistent with the precedent established in Jackson, and seems a more probable judicial approach.
Admissibility of Expert Neuropsychological Testimony
The basic equivalence of clinical psychologists and medical doctors to provide testimony regarding a defendant’s mental state in criminal cases was first acknowledged in Jenkins v. United States (1962), which eschewed the medical/nonmedical distinction in favor of evaluating the probative value of the testimony to aid the trier-of-fact. However, challenges to the admissibility of neuropsychological evidence have arisen in several recent civil cases (cf. Satz, 1988; Schwartz, 1987). The first two cases moved to limit or exclude neuropsychological evidence on the basis that psychologists are not medical doctors, and hence were unqualified to render on opinion regarding the presence of brain damage ( Executive Car & Truck Leasing v. DeSerio, 1985; GIW Southern Valve Co. v. Smith, 1985). In both cases, the Florida Court of Appeals reversed the lower courts’ admission of neuropsychological testimony, effectively excluding neuropsychological evidence.
However, a third civil case (Horne v. Goodson Logging Co., 1985) served to establish the admissibility of neuropsychological testimony. Partly in response to the Florida decisions, the American Psychological Association together with the North Carolina Psychological Association submitted an amicus brief in support of neuropsychological evidence in Horne v. Goodson (Bersoff & Majestic, 1986). Apparently the brief was influential in this case. The North Carolina Court of Appeals upheld the admissibility of neuropsychological evidence, with the credibility of the expert left to the discretion trial court judge.
While these three cases established precedents for the admissibility of neuropsychological evidence in civil proceedings, such evidence has also become an issue in criminal proceedings. In at least one prominent criminal case ( People v. Wright, 1982), the Supreme Court of Colorado determined en banc that a neuropsychologist’s testimony regarding test evidence of minimal brain dysfunction was properly admitted into evidence in support of a defendant’s successful insanity defense.
Rules governing the admissibility of expert psychological evidence vary by jurisdiction and often by the judge hearing a given case, who must determine admissibility in a given case (Lempert & Saltzberg, 1982). The Federal Rules of Evidence (1975; particularly FRE 401-403 and 702-704) establish a relevancy approach, admitting any evidence that the judge determines to be relevant so long as (a) it will assist the trier of fact, and (b) its probative value does not outweigh its prejudicial impact (Monahan & Walker, 1990). Under the FRE, a case could certainly be made for the relevancy of neuropsychological evidence to address criminal-legal issues and aid the trier of fact. Greater care is required, however, to assure that its probative value outweighs its prejudicial impact.
Introducing evidence that the defendant is “brain damaged” can have a powerful impact on judges and jury members, and the clinician must be careful not to overstate what the data really reflect about the defendant’s level of functioning (Matarazzo, 1990; Shapiro, 1988). Simultaneously, as Ziskin and Faust (1988) suggest, there are real limitations to the current state of knowledge in neuropsychology and the neurobehavioral sciences in general, and their criminal/forensic applications in particular. Ethically, the forensic neuropsychologist has a duty both to consider and to address the ways in which a given defendant is adequately represented by the tests selected and the norms applied. The availability of adequate norms has been a problem in clinical neuropsychology, although recent research has improved the situation considerably (cf. Bernard, 1989; Heaton et al., 1991; Spreen & Strauss, 1991). To ensure that neuropsychological testimony is more probative than prejudicial, it is incumbent upon the expert to know and to be explicit about the limitations of the available norms as they apply in a given case (cf. Golding, 1990; Matarazzo, 1990).
Other rules specific to the admissibility of scientific evidence arise from Frye v. U.S. (1923). Frye established a “general acceptance” test, requiring that the scientific evidence introduced must be established and recognized in the particular field of expertise in order to be admitted into evidence. National surveys of the mainstream methods of neuropsychological assessment (cf. Guilmette, Faust, Hart, & Arkes, 1990; Seretny, Dean, Gray, & Hartledge, 1986) suggest that the Halstead-Reitan Battery, the Luria-Nebraska Battery, and Kaplan’s (1990) “process/qualitative” approach are generally accepted methods, and hence clearly satisfy the Frye test.
Finally, an alternative to the Frye test that has often been applied to novel psychological evidence are the criteria established in Dyas v. United States (1977). The Dyas criteria set forth a three-pronged test of “expertness,” requiring that:
1. the substance of the testimony be “so distinctively related to some science, profession, business or occupation as to be beyond the ken of the average layman,”
2. that “the witness must have sufficient skill, knowledge, or experience in that field or calling as to make it appear that his opinion or inference will probably aid the trier in his search for truth,” and
3, that expert testimony is inadmissible if “the state of the pertinent art or scientific knowledge does not permit a reasonable opinion to be asserted even by an expert.”
The third prong of the Dyas test was further clarified in a subsequent case ( Ibn Tamas v. U.S., 1979) in which the court established that it “begins and ends with a determination of a particular scientific methodology, and not an acceptance, beyond that, of a particular study’s results based on that methodology” (as quoted by Monahan & Walker, 1990, p. 343).
An argument can be made for neuropsychological testimony on each of these three points. First, neuropsychology is clearly an area of specialized knowledge that falls beyond the ken of the layman. The determination of the neuropsychologist witness’s skill is a judicial prerogative [as affirmed in Horne v. Goodson (1985) and People v. Wright (1982)], and generally can be established on voir dire. Guilmette and Giuliano (1991) discuss the research findings related to witness skill, examining training, experience, and judgment accuracy. They note that while proper training is important to accurate judgments, greater experience does not necessarily result in greater diagnostic accuracy. In fact, properly trained neuropsychologists with less experience are generally as accurate as or more accurate than those with more experience. Finally, the state-of-the-art in neuropsychology—even bounded by current limitations in the research base—does permit a reasonable opinion on many issues of direct relevance in criminal proceedings. The substance of this prong (as interpreted in Ibn-Tamas) is generally consistent with the “general acceptance” test established in Frye, and mainstream neuropsychological tests clearly meet this standard.
Discussion
This article has explored some of the potential forensic applications of clinical neuropsychology to issues in the criminal law. The documented presence of brain damage—in and of itself—is not an adequate basis for legal decision making. Rather, what is required is a clear and systematic exposition of the nature, extent, and course of the defendant’s brain dysfunction, and a careful explanation of the consequences this has in terms of the behavior of the defendant relative to the psycholegal issue at hand. Clinical neuropsychology holds significant potential to inform legal decision making in the criminal law, although much of that potential is currently uptapped.
Although the current state of the art in clinical neuropsychology arguably meets the criteria for admissibility, more research is needed to advance the scientific foundation for opinions regarding the neuropsychological parameters of criminal/forensic issues (Grisso, 1987; Matarazzo, 1987). Neuropsychology is an area of rapid growth in which new and exciting data are being produced each year. Studies are appearing that address areas criticized by Ziskin and Faust (1988), including norms over the life span (Faibish, Auerbach, & Thornby, 1986; Heaton et al., 1991; Yeudall, Reddon, Gill, & Stefanyk, 1987), racial, ethnic, and cultural differences in test performance (Bernard, 1989), and the effects of age, education, IQ, gender, and alcohol abuse on neuropsychological test performance (Heaton et al., 1991; Leckliter & Matarazzo, 1989; Matarazzo, 1990). In conjunction with newer neuroradiological techniques (e.g., PET, SPECT), researchers are now able to assess the brain’s regional response to the “challenge” of specific neuropsychological tests (cf. Chase et al., 1984; Parks et al., 1989; Posner, Peterson, Fox, & Raichle, 1988).
However, additional ecologically valid research is still needed to address these and other issues, including (a) behavioral sequelae of localized brain lesions, (b) violence and brain function, (c) base rates in forensic populations, and (d) studies relevant to legal criteria such as predictions of restorability to fitness. The future value of criminal/forensic neuropsychology can be expected to increase as a direct function of advances in these areas of the established knowledge base. The challenge for the present is to bring forensic neuropsychological evidence into the criminal courtroom and establish the value of its contributions to legal decision making in the criminal law.