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Psychopathy and cerebral asymmetry in semantic processing
Person.
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01%
Vol.
9, No.
2, pp. 329-337.
1988
0191~8869,88
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PSYCHOPATHY AND CEREBRAL ASYMMETRY IN SEMANTIC PROCESSING ROBERT D. HARE and JEFFREY W. JUTAI* Department of Psychology, University of British Columbia, Vancouver, Canada V6T lY7 (Received
23 April 1987)
Summary-A divided visual field (DVF) procedure was used to investigate the cerebral organization of language processes in psychopaths. The subjects consisted of four groups of 13 right-handed males: noncriminals (NC), and criminals with high (H), medium (M), and low (L) scores on the Psychopathy Checklist (Hare, 1980). The subject had to decide if a concrete noun, tachistoscopically presented in either the left (LVF) or the right visual hemifield (RVF), matched a pretrial work (SR task),or wasan exemplar of a specificcategory (SC task) or an abstract category (AC task). There were no group differences in reaction time. As predicted, group differences in errors were confined to the AC task; Groups L and NC made fewer RVF than LVF errors (thus showing the sort of RVF advantage expected with semantic categorization), whereas the opposite was true of Group H. The results, along with those obtained in a recent dichotic listening study, lead us to speculate that psychopathy may be associated with weak or unusual lateralization of language function, and that psychopaths may have fewer left hemisphere resources for processing language than do normal individuals.
INTRODUCTION
Very little is known about the structure and dynamics of language processes in psychopaths. Although their primary verbal abilities appear to be intact (Hare, Frazelle, Bus and Jutai, 1980). perplexing inconsistencies often occur between their behavior and their verbalized intentions and feelings. Cleckley (1976) speculated that these inconsistencies are associated with dissociations among the formal, semantic, and affective components of language, dissociations that are concealed in mechanically correct speech. The results of a recent study by Williamson, Harpur and Hare (1986) indicate that there may indeed be something odd about the way in which the various components of language are integrated in psychopaths. The study involved a lexical decision task in which subjects had to decide whether or not stimuli presented via a tachistocope were words. Unlike other criminals (as well as noncriminals), psychopaths failed to show any behavioral (reaction time) or electrocortical (event-related potentials) differentiation between neutral and affective words. The purpose of the present study was to provide additional data on the ways in which psychopaths process language. There are many ways of investigating language processes in normal and pathological populations. Particularly useful are lateralized information-processing tasks that permit inferences to be made about cerebral asymmetries in the organization of language. These include dichotic listening, in which different verbal stimuli are presented simultaneously to each ear, and the divided visual field (DVF) technique, in which verbal stimuli are presented in the right visual hemifield (RVF) or the left visual hemifield (LVF). Although dynamic processes can influence the direction and degree of performance asymmetries (Cohen, 1982), right ear and RVF advantages typically are obtained with verbal material (Beaumont, 1982; Bryden, 1982). This is in accord with one of the most salient features of human communication, namely that for most people language function is controlled primarily by the left cerebral hemisphere. Furthermore, the convergence of dichotic listening and DVF findings suggests that fundamental neural organization may be among those essential aspects of language that are not modality specific (Klima and Bellugi, 1979; Morton, 1980). The results of a recent dichotic listening study have raised the possibility that psychopathic criminals may display an unusual pattern of performance asymmetry when processing some types *Present address: Department PAID 92--1
of Psychology, University of Alberta, Edmonton, 329
Alberta, Canada T46 2E9.
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of verbal information. Hare and McPherson (1984) found that the verbal dichotic listening performance of psychopaths was significantly less lateralized in favor of the right ear than was that of noncriminals and other criminals. Instructions to selectively attend to one ear did not alter the pattern of results. In an early DVF study, Hare (1979) failed to find any differences between psychopaths and other criminals in the asymmetry of visual-field errors. However, the procedure required only simple recognition of common words, and it was suggested that group differences might emerge with tasks that require a greater degree of semantic involvement. In this regard, there is increasing evidence that hemispheric asymmetries, as well as individual differences in these asymmetries, tend to emerge at comparatively late stages in the information-processing sequence, e.g. at a time when percepts make contact with stored representations from memory (Moscovitch, 1979). In an attempt to increase semantic processing requirements, Jutai (1980) had right-handed male criminals perform a DVF version of a task that was originally used to study retrieval from long term memory as a function of semantic category size (Collins and Quillian, 1970; Landauer and Freedman, 1968). Briefly, subjects processed verbal stimuli (concrete nouns), presented in either the RVF or the LVF, under three different conditions. In the simple recognition (SR) task the subject merely had to decide whether or not a given word matched a pre-trial cue word. The other conditions required the subject to make a semantic judgment about the test word. In the specific categorization (SC) task, he had to determine whether or not a given word was an exemplar of a relatively specific or concrete semantic category. In the abstract categorization (AC) task, the subject had to determine whether or not a given word was a member of a more abstract semantic category. There were no visual field asymmetries in reaction time (RT) or error rate (ER) during performance of the SR task. RT and ER asymmetries were obtained with the SC and AC tasks, but in opposite directions. The SC task produced the RVF-left hemisphere superiority expected with semantic categorization (cf. Cohen, 1982; Wood, Taylor, Penny and Stump, 1980). But when judgments were required about inclusion of words in a larger semantic category (AC condition), superiority shifted to the LVF-right hemisphere. This difference between the SC and AC tasks in asymmetry was larger for inmates with high scores on the Psychopathy Checklist (PCL; Hare, 1980) than for those with low scores, but the effect did not reach statistical significance. In the present study we provide additional data on psychopathy and information processing asymmetry during semantic categorization. The procedure was basically the same as in the experiment by Jutai (1980); however, the sample size and the number of trials in each task were increased, and a noncriminal comparison group was added. A larger number of trials was used in order to obtain more stable estimates of asymmetry and because of the evidence that in normal subjects left hemisphere involvement in information processing may increase with stimulus familiarity and time on task (Zaidel, 1979). On the basis of out previous research we expected that, compared with the other subjects, psychopaths would show reduced or even reversed processing asymmetry on the AC task, but not on the SR or SC tasks. The dependent variables were RT and ER. We recognize that speed and accuracy measures of performance in DVF tasks do not necessarily tap the same mental processes, nor are they readily interchangeable (Zaidel, 1983). The use of RT as a dependent variable allowed us to determine whether or not there were group differences in the speed of semantic processing, whereas ER provided information on the quality of semantic processing. The joint use of RT and ER also helped us to determine if any group differences in ER were the result of speed-accuracy tradeoffs. METHOD Subjects The criminal subjects were 39 white male inmates of a medium security institution who had volunteered to take part in the study and who had agreed to provide informed consent and permission to inspect their institutional files. Each inmate was consistently right-handed, that is, indicated a preference for using the right hand for each activity listed in a lateral preference questionnaire (Porac and Coren, 1981). Two experienced research assistants (not those who conducted the experiment) used semi-structured interviews and case-history data to independently
Psychopathy and cerebral asymmetry in semantic processing Table
I. Characteristics
Age GrOUD
H M L NC
331
of each group
Education
IQ
M
SD
M
SD
-M
SD
28.9 28.5 30.2 30.8
6.1 1.6 7.2 8.3
Il.1 10.6 10.4 10.5
3.0 2.9 3.3 1.3
102.7 100.6 102.1 -
12.6 13.4 12.8 -
N = I3 each group. NC = noncriminals; H. M. and L = criminals with high, medium, and low scores, respectively. on the Psychopathy Checklist. IQs were not available for Group NC.
fill out the 22-item PCL for each inmate. The PCL, described in detail elsewhere (Hare, 1980, 1985), is based on the clinical profile of the psychopath provided by Cleckley (1976). Each item is scored on a 3-point scale (0, 1, 2) according to the extent to which it applies to the inmate; total scores can range from 0 to 44. A psychometric analysis of the PCL in a sample of 301 inmates yielded classical test theory indices of reliability (inter- and intrarater correlations, alpha coefficients) of 0.82 to 0.93, and a generalizability coefficient of 0.90 (Schroeder, Schroeder and Hare, 1983). The interrater reliability of PCL scores in the present experiment was 0.88. Comparisons between the PCL and other procedures for the assessment of psychopathy can be found in Hare (1985). PCL scores were used to divide the inmates into high (H), medium (M), and low (L) psychopathy groups. Group H consisted of 13 inmates with a mean checklist score greater than 32 (M = 35.1, SD = 2.2). Group L consisted of 13 inmates with a mean checklist score less than 23 (M = 16.9, SD = 4.2). The remaining 13 inmates constituted Group M (M = 225.9, SD = 2.6). A noncriminal comparison group (NC) consisted of 13 consistently right-handed men recruited from a federal employment center; their demographic and socioeconomic characteristics were similar to those of the inmates. Although the procedures used with these subjects were the same as those used with the criminals, the context in which they were administered was clearly not the same. However, there is no theoretical reason to suspect that incarceration has any effect on information processing asymmetry. The demographic characteristics of each group are presented in Table 1. None of the group differences were significant. All subjects were in good general health and had normal or corrected-to-normal eyesight. Stimulus materials
and apparatus
The stimulus was a 4-letter concrete noun printed vertically (with black Letraset) on a white card, and located either to the left or the right of a digit (l-9) printed at the central fixation point. The stimuli were presented in a 2-field Cambridge tachistoscope; the inner edges of the word and the digit subtended a visual angle of 1.5”. A set of blank cards containing only a central fixation digit was also constructed to serve as a check on compliance with task instructions and requirements. The center of the pre-exposure field was occupied by a fixation dot. Stimulus presentation followed, by approx 1 set, a verbal “ready” signal. Stimulus duration was 80 msec. Reaction time was recorded by an electronic timer which stopped when the subject pressed one of two microswitches; these were located on either side of the left- or right-hand thumb, and were used to indicate a YES or NO response. The microswitches were connected to a panel housing a red and a green light, each labelled either YES or NO. Neither piece of equipment was visible to the subject. Procedure
Two research assistants conducted the experiment; both were blind to the diagnosis of the subjects. The subject was instructed to do two things on each trial, in the following order: (1) respond to the stimulus as quickly and accurately as possible by pressing the appropriate microswitch with his thumb, without saying anything aloud; and (2) when signalled by the experimenter (immediately after reaction time had been recorded) report, in order, the fixation digit and stimulus word perceived. The importance of central fixation was stressed. The light panel was monitored to ensure that the subject’s manual responses matched his verbal reports.
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ROBERT D. HARE and JEFFREY W. JUTAI
Each subject performed all three tasks, in counterbalanced order. There were 128 trials in each task, 96 word trials and 32 blank trials. In each type of task the subject was shown a cue word (or words) before each trial; the cue word was printed in large block letters on a white card placed above the tachistoscope. In the SR task the subject was instructed to indicate whether or not the stimulus word presented in the LVF or the RVF matched the cue word, which it did on half of the trials. In the SC task the cued category was one of the following: FOUR-FOOTED ANIMAL, BIRD, VEHICLE, WEAPON. There were 32 trials with each category. On each trial the subject was instructed to indicate whether or not the stimulus word presented in the tachistoscope was a member of the cued category, which varied from block to block (4 blocks in all). Category order was counterbalanced across subjects. The AC task was similar to the SC task except that the cued category was LIVING THING? The order in which stimulus words were presented in a given task, and the visual field in which they appeared, were randomly determined. The same words were presented in each visual field, but not in the same order. The hand used to make a response and the direction of the thumb movement involved (flexion or extension) were counterbalanced across subjects and within tasks. On blank trials the subject was required to withhold his motor response, and then, when prompted, to report the fixation digit and tell the experimenter that no word was seen. The three tasks had similar stimulus and response features but different cognitive processing requirements. In this way we hoped that comparisons between the tasks would not be compromised by the confounding of sensory-motor with cognitive demands. Several practice trials were given prior to the start of each task. Trials in which the subject failed to respond by depressing the microswitch (except blank trials) were repeated at the end of the task involved. In general, each task was performed without difficulty, and there was seldom any need for more than one or two repeat trials. When the subject depressed the microswitch on two successive blank trials, he was reminded that he was to respond accurately as well as quickly. The entire experiment lasted about 2: hr. Each subject was paid $10 for his participation. Data analysis
Storable trials were those on which the subject had fixated centrally (i.e. accurately reported the fixation digit) and on which there was correct recall of the stimulus word immediately after registration of a YES/NO decision. These particular criteria were adopted to ensure that the functional stimulus for the subject was in fact a perceived word. Responses on the blank trials were not scored. There were no group differences in the percentage of storable trials; each group had at least 90% of their data available for analysis. Preliminary analyses indicated that none of the effects reported below were related to the hand used to make a response, and we therefore pooled the data across hands. In order to determine if there were any group differences in RT or ER asymmetry as a function of time on task, we divided the 128 trials on each task into two 64-trial blocks, in the order in which they were experienced by each subject. Group (H, M, L, NC) x Task (SR, SC, AC) x Visual Field (LVF, RVF) x Block (1, 2) repeated-measures analyses of variance (ANOVA) were performed on the RT and ER data, using the BMD P2V program (Dixon, 1983). The P values reported for effects involving repeated measures are Greenhouse-Geisser probabilities in which departures (generally small) from the homogeneity of covariance assumption were taken into account. Although we report the results of the ANOVAs, our primary interest was in the 3-way interaction involving group (H, M, L, NC), visual field (LVF, RVF), and task (SR, SC, AC). That is, we expected that Group H would differ from the other groups in performance of the AC task but not in performance of the SR or SC tasks. Two sets of 3 planned interaction comparisons between means (one set for ER and one set for RT) were made using Bonferroni t statistics (Kirk, 1968, pp. 79-81; Marascuilo and Levin, 1983, pp. 4547). In these comparisons (one for each task) the mean performance asymmetry (RVF-LVF) for Group H was compared with that of all the other groups combined; that is, H versus (M f L + NC)/3. The familywise Type I error rate was held at 0.01 for each set of planned comparisons. The magnitude and psychological significance of a performance asymmetry calculated from raw scores may be influenced by individual differences in overall level of performance (see Bryden, 1982;
Psychopathy and cerebral asymmetry in semantic processing
333
Marshall, Caplan and Holmes, 1975). For this reason, we calculated a laterality coefficient for each subject and task; the formula was (RVF ER - LVF ER)/(RVF ER + LVF ER). We also analyzed the data using simple differences in ER between the RVF and the LVF as the dependent variable. In each case the results led to the same statistical conclusions as those obtained with the raw scores. Because much of the RT and ER data were positively skewed, they were subjected to various transformations. The statistical conclusions were unchanged, and only analyses of the raw data are reported here. RESULTS Reaction time RTs were calculated only for storable trials on which the subject made a correct YES/NO decision. None of the planned Bonferroni comparisons between means were significant. The main effect of task was significant, F (2,96) = 22.3, P < 0.001; Tukey HSD tests indicated that RTs were faster on the SR task (M = 0.984 set) than on either the SC (M = 1.264 set) or the AC (M = 1.225 set) tasks, and that the latter two tasks did not differ from one another. RTs were usually faster in the RVF (M = 1.150 set) than in the LVF (M = 1.162 set), but the effect was not significant (P c 0.10). There was a general decrease in RT from Block 1 to Block 2 (P < O.Ol), with the decrease being greater (P < 0.05) for the SR task than for the SC and AC tasks. Error rate Errors consisted of failures to correctly decide whether or not stimulus words were matches (SR condition) or category exemplars (SC and AC conditions). Because a trial was deemed scorable only if the subject had accurately recalled the stimulus, an error was more likely to have been an error of judgment or of stimulus evaluation than a failure in perception. Error rate was defined as the percentage of storable trials on which an incorrect response was given. The results are presented in Table 2. Analysis of variance yielded a significant main effect of task, F (2, 96) = 3.74, P < 0.05. Tukey HSD tests indicated that fewer errors were made on the SR task than on the SC and AC tasks. The Group x Visual Field x Task interaction was significant, F (6, interaction comparisons (k = 3, FW = 0.01, 96) = 3.79, P < 0.005. Planned Bonferroni MS, = 9.023) revealed that Group H differed significantly (in visual field asymmetry) from the other groups on the AC task but not on the SR and SC tasks. Inspection of Table 2 clearly indicates that the major way in which Group H differed from Groups L and NC was in showing a large RVF deficit, rather than a RVF advantage, on the AC task. Although the Group x Visual Field x Task x Block interaction was not significant, inspection of the data indicated that group differences in asymmetry during performance of the AC task were Table 2. Mean error rate as a function of group. task and visual field Task SR Grouo
SC
AC
LVF
RVF
LVF
RVF
LVF
RVF
SD
5.52 4.42
4.89 4.63
a.18 6.27
a.05 5.50
4.99 7.74
9.00 7.26
M
5.60
SD
7.71
4.34 5.99
7.62 4.79
7.15 6.19
6.65 5.55
7.68 5.90
M SD NC M SD
5.30 4.12
3.87 2.96
6.26 5.37
7.22 a.95
7.39 7.92
5.60 4.48
2.60 3.00
2.75 3.58
5.91 6.28
4.32 5.09
4.12 3.57
2.27 2.67
H M M
L
N = 13 each group. NC = noncriminals; H. M. and L-criminals with high, medium, and low scores, respectively, on the Psychopathy Checklist. LVF = left visual field; RVF = right visual field. SR = simple recognition; SC = specific categorization; AC = abstract categorization.
ROBERT D. HARE and
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JEFFREY W. JL.TAI
larger on Block 2 than on Block 1. Thus, on Block 1 the ER for the LVF and the RVF, respectively (in brackets), was as follows: Group NC (4.64, 3.81); Group L (8.37, 9.03); Group M (8.39, 9.67); and Group H (5.01, 7.36). The corresponding ER on Block 2 was as follows: Group NC (2.56, 0.96); Group L (6.41, 3.05); Group M (4.91, 5.-69); and Group H (4.98, 10.64). Time on the AC task was associated with an increase in the RVF advantage shown by Groups L and NC, primarily because of a reduction in RVF errors. On the other hand, Group H showed an increase in the LVF advantage, entirely the result of an increase in RVF errors. The laterality coefficients provide a good indication of the changes in performance asymmetry from Block I to Block 2; they are illustrated in Fig. 1. Speed-accuracy
tradeoff
It is very unlikely that the performance of Group H on the AC task was the result of a speed-accuracy tradeoff (cf. Pachella, 1974). Correlations between RT and ER measures were generally small and nonsignificant. For example, the product-moment correlation between RT and ER during performance of the AC task was 0.03 for the LVF and 0.15 for the RVF. DISCUSSION
None of the RT differences among Groups H, L and NC were significant. Each group responded somewhat faster to stimuli presented in the RVF than to those presented in the LVF. RTs were generally faster in the SR task than in the AC task, confirming that the semantic processing requirements of the AC task were more demanding than were those of the SR task. Although the differences were not significant, it is worth mentioning that the RTs of Group H were similar to those of the noncriminals and faster than those of the other criminal groups. The pattern of errors displayed by Groups L and NC-a larger RVF advantage during abstract categorization than during simple recognition of verbal information-is consistent with the general literature on asymmetries in semantic processing (e.g. Cohen, 1982; Day, 1977; Gibson, Dimond and Gazzaniga, 1972; Wood et al., 1980). Apparently in normal right-handed individuals “template” matching of verbal material can be handled readily by either hemisphere, whereas semantic categorization is better handled by the left hemisphere (Zaidel, 1978). The major finding of this study was that psychopathic criminals differed from other criminals and noncriminals in the asymmetry of errors associated with performance of an abstract categorization task. Specifically, Group H displayed normal asymmetry on the SR task, but reversed asymmetry (an apparent LVF advantage) on the AC task. This reversed asymmetry was largely the result of an unusually large number of errors in the RVF, and it may therefore be more reasonable to refer to it as a RVF deficit rather than as a LVF advantage. Unlike Groups L and NC, Group H (and, to a lesser extent, Group M) failed to show an improvement in RVF performance with time on the AC task; as a result, group differences in
Block 1
Block 2
Fig. 1. Mean ER laterality coefficient (RVF - LVF/RVF + LVF) obtained by each group on the abstract categorization (AC) task during Blocks I and 2. Values above the line indicate a relative RVF advantage and those below the line a relative LVF advantage.
Psychopathy and cerebral asymmetry in semantic processing
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processing asymmetry were more evident in Block 2 than in Block 1. This may account for Jutai’s (1980) failure to obtain significant group differences in the same AC task; Jutai gave his subjects only 32 trials per task whereas we gave them 128. Group H’s RVF errors on the AC task were not the result of a speed-accuracy tradeoff; the correlations between RT and ER were uniformly small, and the increase in RVF ER on Block 2 was not associated with a reduction in RVF RT. It is also unlikely that the increase in Group H’s RVF errors in Block 2 were the simple result of an increase in mental fatigue or boredom, or of a decrease in motivation, unless we assume that these factors primarily affected RVF performance, and then only on the AC task. Group H’s unusual processing asymmetry during semantic categorization occurred with ER, but not with RT, as the dependent variable. However, it is not unusual to obtain divergent RT and ER results in DVF tasks; these two variables probably do not tap the same mental processes. Moreover, there is some evidence that accuracy measures of performance are more sensitive than is RT to semantic dysfunction (Grober, Perecman, Kellar and Brown, 1980; Semenza, Denes, Lucchese and Bisiacchi, 1980). Our DVF results are consistent with the dichotic listening results reported by Hare and McPHerson (1984); Both sets of data raise the possibility that psychopaths differ from other right-handed males in the asymmetries associated with performance of at least some types of lateralized verbal tasks. Future research will determine if these findings can be replicated, and, if so, if similar differences exist during processing of other lateralized input, both verbal and nonverbal. Meanwhile, several tentative interpretations of the dichotic listening and DVF data can be offered. Thus, we consider the possibility that psychopathy may be associated with one or more of the following: (1) the use of unusual strategies to process some types of verbal information; (2) asymmetrically low left-hemispheric arousal; and (3) weak lateralization of language functions. With respect to the first interpretation, the dichotic and DVF performance of the psychopaths may have reflected the use of perceptual-cognitive strategies (voluntary and involuntary) that differed from those used by the other subjects. At present, there is little indication of what these strategies might be, but one possibility is that there were group differences in attentional bias while the tasks were being performed. For example, it might be argued that the psychopaths’ performance on the dichotic listening task (Hare and McPherson, 1984) and on the abstract categorization (AC) task in the present study was related to a leftward attentional bias, whereas their performance on the simple recognition (SR) task was related to a rightward attentional bias. This seems unlikely for several reasons. For one thing, there is no logical reason why psychopaths should have a rightward attentional bias for one verbal task and a leftward bias for another verbal task. Moreover, it is possible to manipulate attentional biases with appropriate instructions (see Geffen and Quinn, 1984). But when Hare and McPherson (1984) instructed psychopaths to attend to and report only words heard in the right ear, their right ear advantage did not improve, suggesting that something other than group differences in attentional processes were responsible for the differences among groups in dichotic listening performance. Similarly, it is very likely that the nature of the AC task used in the present study resulted in much heavier demands being placed on memory and semantic processes than on attentional mechanisms. Moreover, even when tasks involve only lexical decisions, subject-directed shifts in attention have no significant effect on visual field differences in speed or accuracy of performance (Hardyck, Chiarello, Dronkers and Simpson, 1985). Several investigators have proposed that performance asymmetries, as well as some personality and psychophathological processes, are related to enduring (trait rather than state) differences in hemispheric arousal (e.g. Hellige, 1983; Levy, 1983; Levy, Heller, Banick and Burton, 1983; Tucker, 198 1). Thus, rightward asymmetries may reflect characteristically high left-hemisphere arousal, whereas leftward asymmetries may reflect characteristically high right-hemisphere arousal. This hemisphericity model might explain our DVF and dichotic listening results by assuming that, for unspecified reasons, the left hemisphere of psychopaths is in a chronic state of underarousal (see Tucker, 1981). However, several recent electrocortical studies have failed to find any evidence of an unusual or abnormal balance between left and right hemisphere arousal in psychopaths (Harpur, Williamson, Forth and Hare, 1986; Jutai, Connolly and Hare, 1987; Jutai and Hare, 1983).
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Given the conceptual consistency of results across two modalities and two paradigms, perhaps the most tenable interpretation of our DVF and dichotic listening data is that psychopaths differ from others in the cerebral organization of language (see Hare and McPherson, 1984 for further details). In particular, the data are consistent with the hypothesis that the left hemisphere of psychopaths is not strongly specialized for language and, by implication, that its resources for language processing are more limited than they are in normal individuals. the DVF results suggest, for example, that the left hemisphere of psychopaths may perform verbal matching tasks well but that it may lack the resources needed for the efficient performance of tasks that place heavy demands on semantic processes and memory (Jutai and Hare, 1983; Jutai, Connolly and Hare, 1987). In this regard, we note that the improved RVF performance shown by Groups L and NC with time on the AC task is consistent with Tzeng and Wang’s (1984) proposal that familiarity with a verbal task is associated with a decrease in the importance of purely perceptual factors, and an increase in the importance and use of left hemisphere linguistic resources. The fact that Group H’s RVF performance did not improve with time on the AC task becomes understandable if we assume that the left hemisphere capacity for processing language is more limited in psychopaths than in normal individuals. A similar interpretation can be applied to the dichotic listening results (Hare and McPherson, 1984), in which psychopaths exhibited little asymmetry in dichotic listening performance, even when instructed to attend only to words heard in one ear at a time (Hare and McPherson, 1984). Geffen and Quinn (1984) have argued that the inherent right-ear advantage for recognizing words (because of left-hemisphere specialization for processing speech) may be overcome by voluntary direction of attention to the left ear, but only if processing capacity of the right hemisphere is not exceeded. The failure of psychopaths to improve upon their right-ear performance when attention is focused on the right ear (Hare and McPherson, 1984) suggests that dichotic listening tasks may severely tax limited processing capacity of the left hemisphere. Our speculations about the meaning of the DVF and dichotic listening findings notwithstanding, it must be realized that the results, though statistically significant, were not particularly strong. Moreover, even if subsequent research does confirm that psychopaths differ from others in the . cortical (and perhaps subcortical) organization of language resources, the implications for their behavior would be uncertain (Hare and McPherson, 1984). It is possible that one consequence of weak language asymmetry is a reduction in the effectiveness of operations and mechanisms that involve language, in which case several related possibilities would be worth considering: (1) that the role normally played by language in the regulation of behavior (Luria, 1973) is reduced in psychopaths (Schalling, 1978); (2) that the formal, semantic, and affective components of language are less integrated in psychopaths than in normal individuals (Cleckley, 1976; Williamson et al., 1986); and (3) that psychopaths are less likely than others to use cognitive strategies and overt behaviors that ordinarily rely on the verbal, logical, and sequential operations of the left hemisphere (see Tucker, 198 1). ,&knowledgemenrs-This research was supported by Grant MT-451 1 from the Medical Research Council of Canada. The assistance of Adelle Forth, Leslie McPherson, Sherrie Williamson, John Lind, and Timothy Harpur, and the cooperation of the staff and inmates of Mission Medium Security Institution are gratefully acknowledged.
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Harpur T. J., Williamson S. E., Forth A. E. and Hare R. D. (1986) A quantitative assessment of resting EEG in psychopathic and nonpsychopathic criminals. Psychophysiology 23, 439 (Abstr). Hellige J. B. (1983) Hemisphere x Task interaction and the study of laterality. In Cerebral Hemisphere Asymmetry: Method. Theory, and Applicafion (Edited by Hellige J. B.). Praeger, New York. Jutai J. W. (1980). Psychopathy nnd Semantic Processing. Unpublished master’s thesis, University of British Columbia, Vancouver. Jutai J. W., Connolly J. F. and Hare R. D. (1987). Psychopathy and event-related brain potentials (ERPs) associated with attention to speech stimuli. Person. Indirid. 018 8, 175-184. Jutai J. W. and Hare R. D. (1983) Psychopathy and selective attention during performance of a complex perceptual motor task. Psychophysiology 20, 146-l 5 I. Kirk R. E..(1968). Experimental Design: Procedures for the Behavioral Sciences. Brooks/Cole, Belmont, CA. Klima E. S. and Bellugi U. (1979) The Sizns of Lannurrae. Harvard Univ. Press. Cambridee. MA. Landauer T. K. and Freedman J. L. (1968). Infbrmat~on~etrieval from long-term’memory: Category size and recognition time. J. verb. learn. verb. Behav. 7, 291-295. Levy J. (1983) Individual differences in cerebral hemisphere asymmetry: Theoretical issues and experimental considerations. In Cerebral Hemisphere Asymmefry: Method, Theory, and Application (Edited by Hellige J. G.). Praeger. New York. Levy J., Heller W., Banick M. T. and Burton L. A. (1983). Are variations among right-handed individuals in perceptual asymmetries caused by characteristic arousal differences between hemisphere? J. exp. Psychol. (Hum. Percept. Perform.) 9, 329-359.
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Williamson S. E., Harpur T. J. and Hare R. D. (1986) Behavioral and electrocortical responses of psychopaths to emotional words. Psychophysiology 23, 470 (Abstr.). Wood F., Taylor B., Penny R. and Stump D. (1980) Regional cerebral blood flow response to recognition memory versus semantic classification tasks. Brain Language 9, 113-122. Zaidel E. (1978) Lexical organization in the right hemisphere. In Cerebral Correlates of Conscious Experience. (Edited by Buser P. A. and Rouge&Buser A.). I.N.S.E.R.M. Symposium No. 6. North-Holland Publishing, Amsterdam. .Zaidel E. (1979) On measuring hemispheric specialization in man. In Advanced rechnobiology (Edited by Rybak B.) SijthoII’ and Noordhoff, Amsterdam. Zaidel E. (1983) Advances and retreats in laterality research. Behuv. Bruin Sci. 3, 523-528.
indicid.
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Vol.
9, No.
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PSYCHOPATHY AND CEREBRAL ASYMMETRY IN SEMANTIC PROCESSING ROBERT D. HARE and JEFFREY W. JUTAI* Department of Psychology, University of British Columbia, Vancouver, Canada V6T lY7 (Received
23 April 1987)
Summary-A divided visual field (DVF) procedure was used to investigate the cerebral organization of language processes in psychopaths. The subjects consisted of four groups of 13 right-handed males: noncriminals (NC), and criminals with high (H), medium (M), and low (L) scores on the Psychopathy Checklist (Hare, 1980). The subject had to decide if a concrete noun, tachistoscopically presented in either the left (LVF) or the right visual hemifield (RVF), matched a pretrial work (SR task),or wasan exemplar of a specificcategory (SC task) or an abstract category (AC task). There were no group differences in reaction time. As predicted, group differences in errors were confined to the AC task; Groups L and NC made fewer RVF than LVF errors (thus showing the sort of RVF advantage expected with semantic categorization), whereas the opposite was true of Group H. The results, along with those obtained in a recent dichotic listening study, lead us to speculate that psychopathy may be associated with weak or unusual lateralization of language function, and that psychopaths may have fewer left hemisphere resources for processing language than do normal individuals.
INTRODUCTION
Very little is known about the structure and dynamics of language processes in psychopaths. Although their primary verbal abilities appear to be intact (Hare, Frazelle, Bus and Jutai, 1980). perplexing inconsistencies often occur between their behavior and their verbalized intentions and feelings. Cleckley (1976) speculated that these inconsistencies are associated with dissociations among the formal, semantic, and affective components of language, dissociations that are concealed in mechanically correct speech. The results of a recent study by Williamson, Harpur and Hare (1986) indicate that there may indeed be something odd about the way in which the various components of language are integrated in psychopaths. The study involved a lexical decision task in which subjects had to decide whether or not stimuli presented via a tachistocope were words. Unlike other criminals (as well as noncriminals), psychopaths failed to show any behavioral (reaction time) or electrocortical (event-related potentials) differentiation between neutral and affective words. The purpose of the present study was to provide additional data on the ways in which psychopaths process language. There are many ways of investigating language processes in normal and pathological populations. Particularly useful are lateralized information-processing tasks that permit inferences to be made about cerebral asymmetries in the organization of language. These include dichotic listening, in which different verbal stimuli are presented simultaneously to each ear, and the divided visual field (DVF) technique, in which verbal stimuli are presented in the right visual hemifield (RVF) or the left visual hemifield (LVF). Although dynamic processes can influence the direction and degree of performance asymmetries (Cohen, 1982), right ear and RVF advantages typically are obtained with verbal material (Beaumont, 1982; Bryden, 1982). This is in accord with one of the most salient features of human communication, namely that for most people language function is controlled primarily by the left cerebral hemisphere. Furthermore, the convergence of dichotic listening and DVF findings suggests that fundamental neural organization may be among those essential aspects of language that are not modality specific (Klima and Bellugi, 1979; Morton, 1980). The results of a recent dichotic listening study have raised the possibility that psychopathic criminals may display an unusual pattern of performance asymmetry when processing some types *Present address: Department PAID 92--1
of Psychology, University of Alberta, Edmonton, 329
Alberta, Canada T46 2E9.
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ROBERTD.
HARE and
JEFFREYW. JCTAI
of verbal information. Hare and McPherson (1984) found that the verbal dichotic listening performance of psychopaths was significantly less lateralized in favor of the right ear than was that of noncriminals and other criminals. Instructions to selectively attend to one ear did not alter the pattern of results. In an early DVF study, Hare (1979) failed to find any differences between psychopaths and other criminals in the asymmetry of visual-field errors. However, the procedure required only simple recognition of common words, and it was suggested that group differences might emerge with tasks that require a greater degree of semantic involvement. In this regard, there is increasing evidence that hemispheric asymmetries, as well as individual differences in these asymmetries, tend to emerge at comparatively late stages in the information-processing sequence, e.g. at a time when percepts make contact with stored representations from memory (Moscovitch, 1979). In an attempt to increase semantic processing requirements, Jutai (1980) had right-handed male criminals perform a DVF version of a task that was originally used to study retrieval from long term memory as a function of semantic category size (Collins and Quillian, 1970; Landauer and Freedman, 1968). Briefly, subjects processed verbal stimuli (concrete nouns), presented in either the RVF or the LVF, under three different conditions. In the simple recognition (SR) task the subject merely had to decide whether or not a given word matched a pre-trial cue word. The other conditions required the subject to make a semantic judgment about the test word. In the specific categorization (SC) task, he had to determine whether or not a given word was an exemplar of a relatively specific or concrete semantic category. In the abstract categorization (AC) task, the subject had to determine whether or not a given word was a member of a more abstract semantic category. There were no visual field asymmetries in reaction time (RT) or error rate (ER) during performance of the SR task. RT and ER asymmetries were obtained with the SC and AC tasks, but in opposite directions. The SC task produced the RVF-left hemisphere superiority expected with semantic categorization (cf. Cohen, 1982; Wood, Taylor, Penny and Stump, 1980). But when judgments were required about inclusion of words in a larger semantic category (AC condition), superiority shifted to the LVF-right hemisphere. This difference between the SC and AC tasks in asymmetry was larger for inmates with high scores on the Psychopathy Checklist (PCL; Hare, 1980) than for those with low scores, but the effect did not reach statistical significance. In the present study we provide additional data on psychopathy and information processing asymmetry during semantic categorization. The procedure was basically the same as in the experiment by Jutai (1980); however, the sample size and the number of trials in each task were increased, and a noncriminal comparison group was added. A larger number of trials was used in order to obtain more stable estimates of asymmetry and because of the evidence that in normal subjects left hemisphere involvement in information processing may increase with stimulus familiarity and time on task (Zaidel, 1979). On the basis of out previous research we expected that, compared with the other subjects, psychopaths would show reduced or even reversed processing asymmetry on the AC task, but not on the SR or SC tasks. The dependent variables were RT and ER. We recognize that speed and accuracy measures of performance in DVF tasks do not necessarily tap the same mental processes, nor are they readily interchangeable (Zaidel, 1983). The use of RT as a dependent variable allowed us to determine whether or not there were group differences in the speed of semantic processing, whereas ER provided information on the quality of semantic processing. The joint use of RT and ER also helped us to determine if any group differences in ER were the result of speed-accuracy tradeoffs. METHOD Subjects The criminal subjects were 39 white male inmates of a medium security institution who had volunteered to take part in the study and who had agreed to provide informed consent and permission to inspect their institutional files. Each inmate was consistently right-handed, that is, indicated a preference for using the right hand for each activity listed in a lateral preference questionnaire (Porac and Coren, 1981). Two experienced research assistants (not those who conducted the experiment) used semi-structured interviews and case-history data to independently
Psychopathy and cerebral asymmetry in semantic processing Table
I. Characteristics
Age GrOUD
H M L NC
331
of each group
Education
IQ
M
SD
M
SD
-M
SD
28.9 28.5 30.2 30.8
6.1 1.6 7.2 8.3
Il.1 10.6 10.4 10.5
3.0 2.9 3.3 1.3
102.7 100.6 102.1 -
12.6 13.4 12.8 -
N = I3 each group. NC = noncriminals; H. M. and L = criminals with high, medium, and low scores, respectively. on the Psychopathy Checklist. IQs were not available for Group NC.
fill out the 22-item PCL for each inmate. The PCL, described in detail elsewhere (Hare, 1980, 1985), is based on the clinical profile of the psychopath provided by Cleckley (1976). Each item is scored on a 3-point scale (0, 1, 2) according to the extent to which it applies to the inmate; total scores can range from 0 to 44. A psychometric analysis of the PCL in a sample of 301 inmates yielded classical test theory indices of reliability (inter- and intrarater correlations, alpha coefficients) of 0.82 to 0.93, and a generalizability coefficient of 0.90 (Schroeder, Schroeder and Hare, 1983). The interrater reliability of PCL scores in the present experiment was 0.88. Comparisons between the PCL and other procedures for the assessment of psychopathy can be found in Hare (1985). PCL scores were used to divide the inmates into high (H), medium (M), and low (L) psychopathy groups. Group H consisted of 13 inmates with a mean checklist score greater than 32 (M = 35.1, SD = 2.2). Group L consisted of 13 inmates with a mean checklist score less than 23 (M = 16.9, SD = 4.2). The remaining 13 inmates constituted Group M (M = 225.9, SD = 2.6). A noncriminal comparison group (NC) consisted of 13 consistently right-handed men recruited from a federal employment center; their demographic and socioeconomic characteristics were similar to those of the inmates. Although the procedures used with these subjects were the same as those used with the criminals, the context in which they were administered was clearly not the same. However, there is no theoretical reason to suspect that incarceration has any effect on information processing asymmetry. The demographic characteristics of each group are presented in Table 1. None of the group differences were significant. All subjects were in good general health and had normal or corrected-to-normal eyesight. Stimulus materials
and apparatus
The stimulus was a 4-letter concrete noun printed vertically (with black Letraset) on a white card, and located either to the left or the right of a digit (l-9) printed at the central fixation point. The stimuli were presented in a 2-field Cambridge tachistoscope; the inner edges of the word and the digit subtended a visual angle of 1.5”. A set of blank cards containing only a central fixation digit was also constructed to serve as a check on compliance with task instructions and requirements. The center of the pre-exposure field was occupied by a fixation dot. Stimulus presentation followed, by approx 1 set, a verbal “ready” signal. Stimulus duration was 80 msec. Reaction time was recorded by an electronic timer which stopped when the subject pressed one of two microswitches; these were located on either side of the left- or right-hand thumb, and were used to indicate a YES or NO response. The microswitches were connected to a panel housing a red and a green light, each labelled either YES or NO. Neither piece of equipment was visible to the subject. Procedure
Two research assistants conducted the experiment; both were blind to the diagnosis of the subjects. The subject was instructed to do two things on each trial, in the following order: (1) respond to the stimulus as quickly and accurately as possible by pressing the appropriate microswitch with his thumb, without saying anything aloud; and (2) when signalled by the experimenter (immediately after reaction time had been recorded) report, in order, the fixation digit and stimulus word perceived. The importance of central fixation was stressed. The light panel was monitored to ensure that the subject’s manual responses matched his verbal reports.
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ROBERT D. HARE and JEFFREY W. JUTAI
Each subject performed all three tasks, in counterbalanced order. There were 128 trials in each task, 96 word trials and 32 blank trials. In each type of task the subject was shown a cue word (or words) before each trial; the cue word was printed in large block letters on a white card placed above the tachistoscope. In the SR task the subject was instructed to indicate whether or not the stimulus word presented in the LVF or the RVF matched the cue word, which it did on half of the trials. In the SC task the cued category was one of the following: FOUR-FOOTED ANIMAL, BIRD, VEHICLE, WEAPON. There were 32 trials with each category. On each trial the subject was instructed to indicate whether or not the stimulus word presented in the tachistoscope was a member of the cued category, which varied from block to block (4 blocks in all). Category order was counterbalanced across subjects. The AC task was similar to the SC task except that the cued category was LIVING THING? The order in which stimulus words were presented in a given task, and the visual field in which they appeared, were randomly determined. The same words were presented in each visual field, but not in the same order. The hand used to make a response and the direction of the thumb movement involved (flexion or extension) were counterbalanced across subjects and within tasks. On blank trials the subject was required to withhold his motor response, and then, when prompted, to report the fixation digit and tell the experimenter that no word was seen. The three tasks had similar stimulus and response features but different cognitive processing requirements. In this way we hoped that comparisons between the tasks would not be compromised by the confounding of sensory-motor with cognitive demands. Several practice trials were given prior to the start of each task. Trials in which the subject failed to respond by depressing the microswitch (except blank trials) were repeated at the end of the task involved. In general, each task was performed without difficulty, and there was seldom any need for more than one or two repeat trials. When the subject depressed the microswitch on two successive blank trials, he was reminded that he was to respond accurately as well as quickly. The entire experiment lasted about 2: hr. Each subject was paid $10 for his participation. Data analysis
Storable trials were those on which the subject had fixated centrally (i.e. accurately reported the fixation digit) and on which there was correct recall of the stimulus word immediately after registration of a YES/NO decision. These particular criteria were adopted to ensure that the functional stimulus for the subject was in fact a perceived word. Responses on the blank trials were not scored. There were no group differences in the percentage of storable trials; each group had at least 90% of their data available for analysis. Preliminary analyses indicated that none of the effects reported below were related to the hand used to make a response, and we therefore pooled the data across hands. In order to determine if there were any group differences in RT or ER asymmetry as a function of time on task, we divided the 128 trials on each task into two 64-trial blocks, in the order in which they were experienced by each subject. Group (H, M, L, NC) x Task (SR, SC, AC) x Visual Field (LVF, RVF) x Block (1, 2) repeated-measures analyses of variance (ANOVA) were performed on the RT and ER data, using the BMD P2V program (Dixon, 1983). The P values reported for effects involving repeated measures are Greenhouse-Geisser probabilities in which departures (generally small) from the homogeneity of covariance assumption were taken into account. Although we report the results of the ANOVAs, our primary interest was in the 3-way interaction involving group (H, M, L, NC), visual field (LVF, RVF), and task (SR, SC, AC). That is, we expected that Group H would differ from the other groups in performance of the AC task but not in performance of the SR or SC tasks. Two sets of 3 planned interaction comparisons between means (one set for ER and one set for RT) were made using Bonferroni t statistics (Kirk, 1968, pp. 79-81; Marascuilo and Levin, 1983, pp. 4547). In these comparisons (one for each task) the mean performance asymmetry (RVF-LVF) for Group H was compared with that of all the other groups combined; that is, H versus (M f L + NC)/3. The familywise Type I error rate was held at 0.01 for each set of planned comparisons. The magnitude and psychological significance of a performance asymmetry calculated from raw scores may be influenced by individual differences in overall level of performance (see Bryden, 1982;
Psychopathy and cerebral asymmetry in semantic processing
333
Marshall, Caplan and Holmes, 1975). For this reason, we calculated a laterality coefficient for each subject and task; the formula was (RVF ER - LVF ER)/(RVF ER + LVF ER). We also analyzed the data using simple differences in ER between the RVF and the LVF as the dependent variable. In each case the results led to the same statistical conclusions as those obtained with the raw scores. Because much of the RT and ER data were positively skewed, they were subjected to various transformations. The statistical conclusions were unchanged, and only analyses of the raw data are reported here. RESULTS Reaction time RTs were calculated only for storable trials on which the subject made a correct YES/NO decision. None of the planned Bonferroni comparisons between means were significant. The main effect of task was significant, F (2,96) = 22.3, P < 0.001; Tukey HSD tests indicated that RTs were faster on the SR task (M = 0.984 set) than on either the SC (M = 1.264 set) or the AC (M = 1.225 set) tasks, and that the latter two tasks did not differ from one another. RTs were usually faster in the RVF (M = 1.150 set) than in the LVF (M = 1.162 set), but the effect was not significant (P c 0.10). There was a general decrease in RT from Block 1 to Block 2 (P < O.Ol), with the decrease being greater (P < 0.05) for the SR task than for the SC and AC tasks. Error rate Errors consisted of failures to correctly decide whether or not stimulus words were matches (SR condition) or category exemplars (SC and AC conditions). Because a trial was deemed scorable only if the subject had accurately recalled the stimulus, an error was more likely to have been an error of judgment or of stimulus evaluation than a failure in perception. Error rate was defined as the percentage of storable trials on which an incorrect response was given. The results are presented in Table 2. Analysis of variance yielded a significant main effect of task, F (2, 96) = 3.74, P < 0.05. Tukey HSD tests indicated that fewer errors were made on the SR task than on the SC and AC tasks. The Group x Visual Field x Task interaction was significant, F (6, interaction comparisons (k = 3, FW = 0.01, 96) = 3.79, P < 0.005. Planned Bonferroni MS, = 9.023) revealed that Group H differed significantly (in visual field asymmetry) from the other groups on the AC task but not on the SR and SC tasks. Inspection of Table 2 clearly indicates that the major way in which Group H differed from Groups L and NC was in showing a large RVF deficit, rather than a RVF advantage, on the AC task. Although the Group x Visual Field x Task x Block interaction was not significant, inspection of the data indicated that group differences in asymmetry during performance of the AC task were Table 2. Mean error rate as a function of group. task and visual field Task SR Grouo
SC
AC
LVF
RVF
LVF
RVF
LVF
RVF
SD
5.52 4.42
4.89 4.63
a.18 6.27
a.05 5.50
4.99 7.74
9.00 7.26
M
5.60
SD
7.71
4.34 5.99
7.62 4.79
7.15 6.19
6.65 5.55
7.68 5.90
M SD NC M SD
5.30 4.12
3.87 2.96
6.26 5.37
7.22 a.95
7.39 7.92
5.60 4.48
2.60 3.00
2.75 3.58
5.91 6.28
4.32 5.09
4.12 3.57
2.27 2.67
H M M
L
N = 13 each group. NC = noncriminals; H. M. and L-criminals with high, medium, and low scores, respectively, on the Psychopathy Checklist. LVF = left visual field; RVF = right visual field. SR = simple recognition; SC = specific categorization; AC = abstract categorization.
ROBERT D. HARE and
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JEFFREY W. JL.TAI
larger on Block 2 than on Block 1. Thus, on Block 1 the ER for the LVF and the RVF, respectively (in brackets), was as follows: Group NC (4.64, 3.81); Group L (8.37, 9.03); Group M (8.39, 9.67); and Group H (5.01, 7.36). The corresponding ER on Block 2 was as follows: Group NC (2.56, 0.96); Group L (6.41, 3.05); Group M (4.91, 5.-69); and Group H (4.98, 10.64). Time on the AC task was associated with an increase in the RVF advantage shown by Groups L and NC, primarily because of a reduction in RVF errors. On the other hand, Group H showed an increase in the LVF advantage, entirely the result of an increase in RVF errors. The laterality coefficients provide a good indication of the changes in performance asymmetry from Block I to Block 2; they are illustrated in Fig. 1. Speed-accuracy
tradeoff
It is very unlikely that the performance of Group H on the AC task was the result of a speed-accuracy tradeoff (cf. Pachella, 1974). Correlations between RT and ER measures were generally small and nonsignificant. For example, the product-moment correlation between RT and ER during performance of the AC task was 0.03 for the LVF and 0.15 for the RVF. DISCUSSION
None of the RT differences among Groups H, L and NC were significant. Each group responded somewhat faster to stimuli presented in the RVF than to those presented in the LVF. RTs were generally faster in the SR task than in the AC task, confirming that the semantic processing requirements of the AC task were more demanding than were those of the SR task. Although the differences were not significant, it is worth mentioning that the RTs of Group H were similar to those of the noncriminals and faster than those of the other criminal groups. The pattern of errors displayed by Groups L and NC-a larger RVF advantage during abstract categorization than during simple recognition of verbal information-is consistent with the general literature on asymmetries in semantic processing (e.g. Cohen, 1982; Day, 1977; Gibson, Dimond and Gazzaniga, 1972; Wood et al., 1980). Apparently in normal right-handed individuals “template” matching of verbal material can be handled readily by either hemisphere, whereas semantic categorization is better handled by the left hemisphere (Zaidel, 1978). The major finding of this study was that psychopathic criminals differed from other criminals and noncriminals in the asymmetry of errors associated with performance of an abstract categorization task. Specifically, Group H displayed normal asymmetry on the SR task, but reversed asymmetry (an apparent LVF advantage) on the AC task. This reversed asymmetry was largely the result of an unusually large number of errors in the RVF, and it may therefore be more reasonable to refer to it as a RVF deficit rather than as a LVF advantage. Unlike Groups L and NC, Group H (and, to a lesser extent, Group M) failed to show an improvement in RVF performance with time on the AC task; as a result, group differences in
Block 1
Block 2
Fig. 1. Mean ER laterality coefficient (RVF - LVF/RVF + LVF) obtained by each group on the abstract categorization (AC) task during Blocks I and 2. Values above the line indicate a relative RVF advantage and those below the line a relative LVF advantage.
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processing asymmetry were more evident in Block 2 than in Block 1. This may account for Jutai’s (1980) failure to obtain significant group differences in the same AC task; Jutai gave his subjects only 32 trials per task whereas we gave them 128. Group H’s RVF errors on the AC task were not the result of a speed-accuracy tradeoff; the correlations between RT and ER were uniformly small, and the increase in RVF ER on Block 2 was not associated with a reduction in RVF RT. It is also unlikely that the increase in Group H’s RVF errors in Block 2 were the simple result of an increase in mental fatigue or boredom, or of a decrease in motivation, unless we assume that these factors primarily affected RVF performance, and then only on the AC task. Group H’s unusual processing asymmetry during semantic categorization occurred with ER, but not with RT, as the dependent variable. However, it is not unusual to obtain divergent RT and ER results in DVF tasks; these two variables probably do not tap the same mental processes. Moreover, there is some evidence that accuracy measures of performance are more sensitive than is RT to semantic dysfunction (Grober, Perecman, Kellar and Brown, 1980; Semenza, Denes, Lucchese and Bisiacchi, 1980). Our DVF results are consistent with the dichotic listening results reported by Hare and McPHerson (1984); Both sets of data raise the possibility that psychopaths differ from other right-handed males in the asymmetries associated with performance of at least some types of lateralized verbal tasks. Future research will determine if these findings can be replicated, and, if so, if similar differences exist during processing of other lateralized input, both verbal and nonverbal. Meanwhile, several tentative interpretations of the dichotic listening and DVF data can be offered. Thus, we consider the possibility that psychopathy may be associated with one or more of the following: (1) the use of unusual strategies to process some types of verbal information; (2) asymmetrically low left-hemispheric arousal; and (3) weak lateralization of language functions. With respect to the first interpretation, the dichotic and DVF performance of the psychopaths may have reflected the use of perceptual-cognitive strategies (voluntary and involuntary) that differed from those used by the other subjects. At present, there is little indication of what these strategies might be, but one possibility is that there were group differences in attentional bias while the tasks were being performed. For example, it might be argued that the psychopaths’ performance on the dichotic listening task (Hare and McPherson, 1984) and on the abstract categorization (AC) task in the present study was related to a leftward attentional bias, whereas their performance on the simple recognition (SR) task was related to a rightward attentional bias. This seems unlikely for several reasons. For one thing, there is no logical reason why psychopaths should have a rightward attentional bias for one verbal task and a leftward bias for another verbal task. Moreover, it is possible to manipulate attentional biases with appropriate instructions (see Geffen and Quinn, 1984). But when Hare and McPherson (1984) instructed psychopaths to attend to and report only words heard in the right ear, their right ear advantage did not improve, suggesting that something other than group differences in attentional processes were responsible for the differences among groups in dichotic listening performance. Similarly, it is very likely that the nature of the AC task used in the present study resulted in much heavier demands being placed on memory and semantic processes than on attentional mechanisms. Moreover, even when tasks involve only lexical decisions, subject-directed shifts in attention have no significant effect on visual field differences in speed or accuracy of performance (Hardyck, Chiarello, Dronkers and Simpson, 1985). Several investigators have proposed that performance asymmetries, as well as some personality and psychophathological processes, are related to enduring (trait rather than state) differences in hemispheric arousal (e.g. Hellige, 1983; Levy, 1983; Levy, Heller, Banick and Burton, 1983; Tucker, 198 1). Thus, rightward asymmetries may reflect characteristically high left-hemisphere arousal, whereas leftward asymmetries may reflect characteristically high right-hemisphere arousal. This hemisphericity model might explain our DVF and dichotic listening results by assuming that, for unspecified reasons, the left hemisphere of psychopaths is in a chronic state of underarousal (see Tucker, 1981). However, several recent electrocortical studies have failed to find any evidence of an unusual or abnormal balance between left and right hemisphere arousal in psychopaths (Harpur, Williamson, Forth and Hare, 1986; Jutai, Connolly and Hare, 1987; Jutai and Hare, 1983).
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Given the conceptual consistency of results across two modalities and two paradigms, perhaps the most tenable interpretation of our DVF and dichotic listening data is that psychopaths differ from others in the cerebral organization of language (see Hare and McPherson, 1984 for further details). In particular, the data are consistent with the hypothesis that the left hemisphere of psychopaths is not strongly specialized for language and, by implication, that its resources for language processing are more limited than they are in normal individuals. the DVF results suggest, for example, that the left hemisphere of psychopaths may perform verbal matching tasks well but that it may lack the resources needed for the efficient performance of tasks that place heavy demands on semantic processes and memory (Jutai and Hare, 1983; Jutai, Connolly and Hare, 1987). In this regard, we note that the improved RVF performance shown by Groups L and NC with time on the AC task is consistent with Tzeng and Wang’s (1984) proposal that familiarity with a verbal task is associated with a decrease in the importance of purely perceptual factors, and an increase in the importance and use of left hemisphere linguistic resources. The fact that Group H’s RVF performance did not improve with time on the AC task becomes understandable if we assume that the left hemisphere capacity for processing language is more limited in psychopaths than in normal individuals. A similar interpretation can be applied to the dichotic listening results (Hare and McPherson, 1984), in which psychopaths exhibited little asymmetry in dichotic listening performance, even when instructed to attend only to words heard in one ear at a time (Hare and McPherson, 1984). Geffen and Quinn (1984) have argued that the inherent right-ear advantage for recognizing words (because of left-hemisphere specialization for processing speech) may be overcome by voluntary direction of attention to the left ear, but only if processing capacity of the right hemisphere is not exceeded. The failure of psychopaths to improve upon their right-ear performance when attention is focused on the right ear (Hare and McPherson, 1984) suggests that dichotic listening tasks may severely tax limited processing capacity of the left hemisphere. Our speculations about the meaning of the DVF and dichotic listening findings notwithstanding, it must be realized that the results, though statistically significant, were not particularly strong. Moreover, even if subsequent research does confirm that psychopaths differ from others in the . cortical (and perhaps subcortical) organization of language resources, the implications for their behavior would be uncertain (Hare and McPherson, 1984). It is possible that one consequence of weak language asymmetry is a reduction in the effectiveness of operations and mechanisms that involve language, in which case several related possibilities would be worth considering: (1) that the role normally played by language in the regulation of behavior (Luria, 1973) is reduced in psychopaths (Schalling, 1978); (2) that the formal, semantic, and affective components of language are less integrated in psychopaths than in normal individuals (Cleckley, 1976; Williamson et al., 1986); and (3) that psychopaths are less likely than others to use cognitive strategies and overt behaviors that ordinarily rely on the verbal, logical, and sequential operations of the left hemisphere (see Tucker, 198 1). ,&knowledgemenrs-This research was supported by Grant MT-451 1 from the Medical Research Council of Canada. The assistance of Adelle Forth, Leslie McPherson, Sherrie Williamson, John Lind, and Timothy Harpur, and the cooperation of the staff and inmates of Mission Medium Security Institution are gratefully acknowledged.
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