Journal of Neurolinguistics, Vol. 22, Issue 5. Septiembre de 2009. P: 413-426

Pragmatics, theory of mind and executive functions after a right-hemisphere lesion: Different patterns of deficits Maud Champagne-Lavaua, c, and Yves Joanetteb, c aPavillon Albert-Prvost, Hpital du Sacr-Coeur de Montral, Quebec, Canada bCentre de recherche, Institut universitaire de griatrie de Montral, Quebec, Canada cFacult de mdecine, Universit de Montral, Quebec, Canada Received 14 November 2008; revised 6 February 2009; accepted 15 February 2009. Available online 13 March 2009. Abstract

The occurrence of a right-hemisphere lesion can interfere with pragmatic abilities, and particularly with the processing of non-literal speech acts in which the listener has to identify the speaker's intention. A few studies have shown that RHD individuals may exhibit moderate difficulties in tasks requiring attribution of second-order mental states (ToM), suggesting a link between pragmatic and ToM abilities. Although links seem to exist between pragmatic abilities, ToM and executive functions in other populations, no study had tested those three abilities in RHD individuals to explore the possible co-occurrence of impairments in these three abilities. This study evaluated pragmatic and ToM abilities and executive functions in 15 RHD individuals and 15 healthy control participants. The results suggest that the ability to understand pragmatic aspects of language is closely associated with the ability to make inferences about other people's intentions. More interestingly, the association of ToM deficits with executive dysfunction rather than executive dysfunction alone might be the best predictor of different patterns of pragmatic deficits found in different RHD subgroups of patients.

Keywords: Pragmatic deficit; Theory of mind; Executive dysfunction; Right-hemisphere damaged individuals

1. Introduction

Many studies have emphasized the importance of full access to right-hemisphere language functions to ensure successful social communication ([Code, 1987], [Griffin et al., 2006], [Joanette et al., 1990] and [Tompkins, 1995]). Despite their ability to understand simple sentences, right-hemisphere damaged (RHD) individuals with pragmatic deficits may experience significant communicative disabilities in their everyday life. They can find it difficult to transparently convey a message or an intention. The resulting disability is major since a large proportion of everyday communication makes use of pragmatic aspects of language such as irony, metaphor, or indirect requests. These pragmatic aspects of language require the ability to process more than the literal meaning of an utterance in order to grasp the speaker's intention in a given context, and to decide whether a sentence means what is said or more than what

is said as in the case of indirect request. Sabbagh (1999) refers to this ability as communicative intention. This paper addresses such communication disabilities in association with other cognitive deficits in RHD individuals.

Various studies have found that RHD individuals can show impairments such as inappropriate contextual use of language; lack of comprehension of non-literal aspects of language such as metaphor, humor, sarcasm and indirect speech acts; inability to evaluate the plausibility or incongruity of an event in a given context; and inability to make inferences based on a message and, thus, to manage the implicit content of many speech acts (see Joanette, Champagne-Lavau, Kahlaoui, & Ska, 2007, chap. 19; [Martin and McDonald, 2003] and [Monetta and Champagne-Lavau, in press], for review). For example, Winner and Gardner (1977) observed that RHD individuals selected a literal interpretation of the sentence he had a heavy heart more often than healthy controls (HC), when they were shown pictures representing literal and metaphorical interpretations.

Until now, these studies have clearly indicated that RHD individuals may have problems understanding non-literal language while they are able to understand literal language such as the table is made of wood, suggesting that only high-level language processing is impaired in RHD. These pragmatic deficits, however, are not present in all RHD subjects and patterns of performance may vary from one individual to another ([Ct et al., 2007] and [Martin and McDonald, 2003]). This diversity of patterns highlights the importance of studying RHD subjects' communicative performance on an individual basis ([Brownell and Stringfellow, 1999] and [Caramazza, 1984]) and to look at the cerebral regions that are damaged (Griffin et al., 2006). Given RHD patients' assorted impairments affecting the understanding of irony and metaphor, different cognitive processes such as intention decoding, inhibition and flexibility might be involved in such processing ([Martin and McDonald, 2003] and [Monetta and Champagne, 2004]). Thus, in this paper, we explore the relationship between three different concepts that seem to have substantial overlap (pragmatic understanding, intention decoding, executive dysfunction) in RHD individuals.

Pragmatic interpretationfor example, non-literal language processinghas been defined as a mind-reading exercise involving inferences concerning the speaker's mental state (Grice, 1969). Thus, a deficit in decoding such intentions might result in an impairment in non-literal language understanding ([Happ et al., 1999], [Kaplan et al., 1990] and [Winner et al., 1998]). Indeed, Kaplan et al. and Winner et al. have suggested that the problems individuals with right-hemisphere lesions have in distinguishing a joke or an ironic statement from a lie might be attributed to difficulties in understanding the intentions of a story's protagonist ([Kaplan et al., 1990] and [Winner et al., 1998]). The ability to distinguish a joke from a lie, for example, requires an intact capacity to recognize that others have beliefs that may differ from one's own. In the case of non-literal language, the listener must be able to distinguish what the speaker actually says from what he or she intends to convey. Therefore, a correct interpretation of utterance meaning relies on a correct comprehension of speaker intentions. To understand how a listener can interpret an ironic or false utterance, one must comprehend what the listener knows and what the speaker thinks the listener knows. The ability to form representations of other people's mental states and use these representations to understand, predict and judge their statements and behaviors is referred to as a theory

of mind (ToM) ([Baron-Cohen et al., 1985], [Leslie, 1987] and [Premack and Woodruff, 1978]).

The study of ToM in RHD individuals has recently added to our knowledge of their problems in processing communicative intention, globally referred to as pragmatic impairments. A few studies have found that RHD individuals seem to have a reduced capacity to reason on the basis of the speaker's motivation in the conversation. These studies ([Brownell et al., 2000], [Martin and McDonald, 2003], [McDonald, 1999], [Sabbagh, 1999] and [Winner et al., 1998]) disclosed that RHD individuals may have difficulties assessing speakers' mental states (e.g., beliefs, prior knowledge, intention) and understanding their intentions.

The few studies that have specifically tested the attribution of mental states by RHD individuals systematically report a more or less moderate disturbance of these skills ([Happ et al., 1999], [Siegal et al., 1996], [Surian and Siegal, 2001] and [Winner et al., 1998]). Individuals with right-hemisphere lesions find it more difficult than those with left-hemisphere lesions to make predictions based on the false belief of a character in a story ([Happ et al., 1999] and [Siegal et al., 1996]). RHD individuals seem to have more difficulty correctly answering questions dealing with second-order mental states as opposed to first-order mental states ([Griffin et al., 2006], [Happ et al., 1999], [Siegal et al., 1996], [Surian and Siegal, 2001] and [Winner et al., 1998]). Their problem is related to understanding stories or cartoons that require the attribution of mental states as opposed to stimuli that require non-mental inferences ([Griffin et al., 2006] and [Happ et al., 1999]).

In summary, a few studies have shown that RHD individuals may exhibit moderate difficulties in tasks requiring the attribution of second-order mental states, suggesting possible co-occurrence of pragmatic and ToM impairments.

Given that the executive functions (EF) enable people to adapt their cognitive abilities in a variety of situations, and considering that the rules of conversation change with the context in which each particular conversation occurs, it appears that an intact EF system is necessary to engage in adaptive and effective communication. Barkley (2001) postulated a link between executive functions and communication and social behavior. In light of the psycholinguistic models of non-literal language understanding (Champagne & Joanette, 2004), one might think that an inability to inhibit the automatic processing of information such as the literal meaning of an utterance would always result in the activation of the literal interpretation, even for non-literal utterances.

A deficit in inhibition has been suspected to underlie the impairment in suppressing multiple meanings, making it difficult for RHD individuals to choose the correct meaning in the case of non-literal language (Tompkins, Baumgaertner, Lehman, & Fossett, 1995). Inhibition may be central in suppressing prepotent, salient interpretations in favor of those that are more appropriate in the context. Literal, irrelevant meanings may in some circumstances be more readily accessed than other, perhaps more appropriate, meanings, and the ability to inhibit them may, therefore, play an important role in non-literal language understanding (McDonald & Pearce, 1996).

On the other hand, a lack of flexibility or perseverative thinking would prevent the activation of the non-literal interpretation in a context favoring this interpretation

(McDonald, 2007, chap. 4; see Monetta & Champagne, 2004, for a review). The literature on RHD individuals, for example, suggests that reduced flexibility in terms of rigid fixation on literal meaning could entail problems in conceiving of alternative meanings. Consequently, an utterance would always be perceived as having the same meaning, whatever its context, and whatever that context might imply. Thus, RHD individuals would be less able to understand secondary meanings (Brownell, Potter, & Bihrle, 1986). Studies on non-literal language understanding in RHD individuals have suggested that a lack of inhibition or lack of flexibility could account for their deficit in non-literal language understanding. However, no research has investigated such a correlation with metaphor and indirect request understanding.

In summary, a right-hemisphere lesion seems to lead to disturbed communication skills in some individuals. The ability to communicate depends on high-level capacities through which different cognitive systems interact. Thus, an impairment of one or more of cognitive mechanisms should result in a deficit affecting understanding of pragmatic aspects of language. While hypotheses related to a deficit in ToM and/or an executive dysfunction, such as a lack of inhibition have been proposed to account for these deficits, no study has focused specifically on the relationship between non-literal language understanding, ToM abilities and executive functions in RHD individuals. Therefore, the involvement of executive functions needs to be specifically assessed when dealing with the understanding of pragmatic aspects of language and mental state attribution by RHD individuals. The objective of this work was, therefore, to examine whether pragmatic deficits in RHD individuals do or do not coexist with ToM impairments and/or impairments of executive functions.

2. Method

2.1. Participants

Fifteen right-hemisphere damaged (RHD) participants (nine female and six male) were recruited at the Villa Mdica rehabilitation hospital, the Institut de griatrie de Montral, the Rehabilitation Institute of Montreal, and the Jewish Rehabilitation Hospital of Montreal. They were between 66 and 79 years old (mean: 60.9 11.7) and their education ranged from 9 to 14 years (11.7 3.1). All RHD participants had suffered a single unilateral right-hemisphere damage of vascular origin (ischemic or hemorrhagic) as documented by a CT scan (Table 1). At the time of testing, they were between 1 and 4 months post-CVA.

Table 1.

Demographic and clinical data on the RHD participants.

Participants Sex Age Education (years) Post-onset (months) Lesion site

RHD1 F 63 14 4 Frontotemporoparietal

RHD2 F 66 9 2 Basal ganglia

RHD3 F 75 11 3 Lenticular nucleus

Participants Sex Age Education (years) Post-onset (months) Lesion site

RHD4 M 79 7 2 Internal capsula

RHD5 M 69 12 1.5 Basal ganglia

RHD6 F 64 11 3 Temporoparietal

RHD 7 M 69 9 3 Right frontal

RHD8 F 38 11 1 Right frontal

RHD9 F 64 12 4 Subarachnoid

RHD10 M 46 12 5 Temporoparietal

RHD11 M 63 17 2 Subcortical

RHD12 M 65 16 4 Subcortical

RHD13 F 55 10 2 Right frontal

RHD14 F 41 16 2 Internal capsula

RHD15 F 57 7 2 Lenticular nucleus

Full-size table

A control group was composed of 15 healthy control (HC) participants (eight female and seven male), matched to the RHD participants for age (mean: 60.7 12.8) and educational level (mean: 11.7 3.2). Student t-tests were done to ensure that there were no significant differences in age (t(28) = 1.70, p > 0.05) or educational level (t(28) = 1.70, p > 0.05) between the two groups. All participants were right-handed and native French speakers with no previous psychiatric or alcoholic history. Each participant's IQ was assessed with the seven subtest version (short form) of the WAIS-III ([Pilgrim et al., 1999] and [Wechsler, 1981]). Participants had to have a IQ of more than 85 to be included in the study.

2.2. Materials and procedure

After giving their informed consent, participants were tested individually over five sessions during two weeks in a quiet room. Tasks were administered to all participants in random order.

2.2.1. Executive function assessment

Participants were evaluated on their executive functioning. Standardized neuropsychological tests were chosen (Spreen & Strauss, 1998) to assess whether pragmatic deficit co-occurred with a lack of inhibition or a lack of flexibility. The following tests were administered to determine: (1) their ability to inhibit irrelevant visual information with the classical Stroop test (Stroop, 1935) and verbal information with the French version of the Hayling test1 (Rouleau, 1998); (2) their ability to switch

from one strategy to another, i.e., flexibility, with the Trail-Making test (Reitan & Wolfson, 1993) and the Wisconsin Card Sorting Test (WCST) (Heaton, 1981).

Participants were also evaluated on their verbal fluency, i.e., number of words beginning with the letter P, L, T, with the Neurosensory Center Comprehensive Examination for Aphasia (NCCEA) (Spreen & Benton, 1977). The digit span (Wechsler, 1981) was used to assess working memory. Participants followed the standard protocol for the administration of the executive functioning tasks. Number of errors and/or times was recorded according to guideline of each test.

2.2.2. Pragmatic tasks

Participants were given the metaphor comprehension subtest and the indirect requests comprehension task from a standardized protocol, the Montral d'Evaluation de la Communication protocol (MEC; Joanette, Ska, & Ct, 2004). The protocol has been validated and norms are available for different age and education levels.

2.2.2.1. Metaphor comprehension task

Patients were asked to explain 10 idiomatic metaphors such as mon ami a le coeur gros (my friend has a heavy heart) versus 10 new (non-idiomatic) metaphors such as cet autobus est une tortue (this bus is a turtle). If they were not able to give the correct answer, a multiple choice was proposed, including the literal interpretation, a non-literal correct interpretation and an incongruent interpretation.

2.2.2.2. Indirect request comprehension task

Participants were asked to explain 20 utterances presented either after a context suggesting a literal interpretation or after a context implying a non-literal interpretation of the utterance such as an indirect request (see example in Appendix). If they were not able to give the correct answer, a multiple choice cue was proposed, including the literal interpretation and a non-literal correct interpretation.

In these two tasks, answers were scored according to the MEC guideline. Answers were scored 0, 1 or 2, with 2 being awarded for a full and explicitly correct answer and 1 for a partial or implicit answer for a maximum score of 20 per category (idiomatic metaphor, non-idiomatic metaphor, non-literal interpretation: indirect request, literal interpretation).

2.2.3. Theory of mind (ToM) task

Participants had to read aloud 20 stories requiring attribution of false belief. After that, they had to answer three questions: a question about the attribution of mental state (Ment-Q) in order to judge participants' ability to make inferences about protagonists' mental states (ToM), that is, to understand that the protagonist might have a false belief; a factual question (Fac-Q) in order to evaluate participants' understanding of relevant information in the given context; an inferential question (Inf-Q) in order to assess participants' general inferential abilities. Indeed, a problem with the processing of general inferences is usually suggested to explain problems attributing mental states to others (Happ et al., 1999). This last question did not require attribution of mental state but only general inference.

The stories were of two levels of complexity, involving the attribution of either first-order mental state or second-order mental state (see examples in Appendix). These were randomly presented. Answers were recorded and scored 0, 1 or 2, with 2 being awarded for a full and explicitly correct answer and 1 for a partial or implicit answer (see examples in Appendix).

3. Results

Analyses of variance were performed on pragmatic, ToM and neuropsychological tests. Given multiple testing, the threshold of significance was set to p < 0.01.

3.1. Pragmatic evaluation

A 2 2 repeated-measures ANOVA was conducted on the metaphor and indirect request data. The ANOVA group (RHD and HC) metaphor condition (new and idiomatic) revealed only a marginally significant effect of group (F(1,28) = 4.8; p < 0.037) where RHD participants performed worse than HC participants. The interaction was not significant. The ANOVA group (RHD and HC) request condition (non-literal and literal) revealed a main effect of group (F(1,28) = 14.4, p < 0.001) where RHD participants performed worse than HC participants, and a main effect of condition (F(1,28) = 14.9, p < 0.001) where participants performed worse on literal interpretation than on non-literal interpretation. The interaction was not significant.

Thus, the results of the pragmatic evaluation showed that RHD participants as a group performed worse than HC participants (Fig. 1).

Fig. 1. Results of pragmatic assessment in RHD and HC groups.

3.2. ToM evaluation

A 2 2 3 repeated-measures ANOVA for group (RHD, HC) complexity (first-order and second-order) type of question (Ment-Q, Fac-Q, Inf-Q) was performed on the ToM data. The results showed a main effect of group (F(1,28) = 13.3, p < 0.001), where RHD participants performed worse than HC participants, and a main effect of type of question (F(2,56) = 143.4, p < 0.001). The Tukey HSD revealed that Ment-Q were more difficult to answer than Fac-Q (p < 0.001) and Inf-Q (p < 0.001). There was no main effect of complexity.

The group complexity type of question interaction was significant (F(2,56) = 3.5, p = 0.038). The group type of question (F(2,56) = 4.3, p = 0.018) and group complexity (F(1,28) = 9.65, p < 0.01) interactions were also significant. The triple interaction was decomposed according to group. For the RHD group, the complexity type of question interaction was significant (F(2,28) = 13.8, p < 0.0001). There was no effect of complexity (F(1,14) = 1.79, p > 0.05), whereas there was an effect of type of question (F(2,28) = 113.3, p < 0.0001). Post hoc analysis with Tukey's HSD revealed that in the first-order condition, RHD participants made more errors in answering Ment-Q than Fac-Q (p < 0.001) and Inf-Q (p < 0.001), and more errors answering Inf-Q than Fac-Q (p < 0.001). In the second-order condition, they made more errors answering Ment-Q than Fac-Q (p < 0.001) and Inf-Q (p < 0.001). No difference was found between Fac-Q and Inf-Q in this condition (Fig. 2).

Fig. 2. Results of ToM assessment in RHD and HC groups.

For the HC group, the complexity type of question interaction was significant (F(2,28) = 19.8, p < 0.0001). There was an effect of complexity (F(1,14) = 8.5, p < 0.01), where questions in the second-order condition were more difficult to answer

than questions in the first-order condition. There was also an effect of type of question (F(2,28) = 44.4, < 0.0001). Post hoc analysis with Tukey's HSD revealed that in the first-order and second-order conditions, HC participants made more errors in answering Ment-Q than Fac-Q (p < 0.001) and Inf-Q (p < 0.001), while no differences were found between Fac-Q and Inf-Q (Fig. 2).

To sum up, the results of the ToM evaluation showed that RHD participants performed worse than HC participants and that both groups found Ment-Q more difficult than other types of questions. In addition, unlike the RHD participants, HC participants found questions in the second-order condition more difficult to answer than questions in the first-order condition. Differences were also observed between Fac-Q and Inf-Q in the RHD group, contrary to the HC group.

3.3. Executive function assessment

One-way ANOVAs were performed on the two groups' (RHD and HC) performance on the neuropsychological evaluation (Stroop, Hayling, Trail-making A and B, WCST, fluency and digit span). Scores used in these statistical analyses were time and number of errors for the Stroop's third condition (color/word), scores of the automatic and inhibition condition for the Hayling, time for the Trail-making A and B, number of categories found and number of perseverative errors for the WCST.

The results revealed a significant difference between the two groups for the Stroop test (time), the inhibition condition of the Hayling test, the Trail-making A and B (time), the WCST (category and perseverative errors) and the fluency. No statistical differences were found for the other tests: Stroop (number of errors), automatic condition of the Hayling, and forward and backward digit span (cf. Table 2).

Table 2.

Results of neuropsychological evaluation for RHD and HC groups.

RHD (mean [SD]) HC (mean [SD]) F p

Stroop (Colors/words, time in s) 46.05 [18] 31.22 [10.4] 7.64 0.010*

Stroop (errors) 2.27 [2.4] 1.13 [1.1] 2.73 0.109

Hayling (automatic) 5.90 [0.7] 6.46 [0.5] 5.60 0.025

Hayling (inhibition) 8.50 [2.06] 12.20 [1.2] 37.21 0.0001*

Trail-making A (time in ms) 84.30 [42.4] 38.40 [12.1] 16.20 0.0001*

Trail-making B (time in ms) 187.42 [117.8] 71.84 [60.6] 13.53 0.001*

WCST (number of categories) 2.26 [1.9] 5 [1.1] 22.76 0.0001*

WCST (number of perseverative errors) 47.80 [24.8] 12.90 [11.4] 24.51 0.0001*

RHD (mean [SD]) HC (mean [SD]) F p

Fluency 29.47 [13.9] 44.40 [13.7] 8.77 0.006*

Digit span forward 8.73 [1.9] 10.06 [1.8] 3.89 0.058

Digit span backward 4.80 [1.8] 6.26 [1.7] 5.06 0.033

Full-size table

*Indicates significant differences. By multiple testing, the threshold of significance was set to p < 0.01.

To sum up, these results indicate that the RHD group performed significantly worse than the control group on tests that evaluate inhibition and flexibility (Trail-making and WCST).

3.4. Different patterns of RHD performances

Looking at the different pragmatic performances of RHD participants, some RHD participants seemed to behave differently than others. A hierarchical cluster analysis (Ward's method) was undertaken according to RHD performance on pragmatic evaluation to characterize different profiles among them. Ward's method is a minimum distance hierarchical method which calculates the sum of squared Euclidean distances from each case in a cluster to the mean of all variables. This method minimizes the sum of squares of any pair of clusters to be formed at a given step. This cluster analysis was only based on RHD performances on new metaphor, idiomatic metaphor, indirect request and literal interpretation instead of their overall level of severity.

Four clusters were found (cf. Fig. 3) suggesting three patterns of performance: RHD-U (Unimpaired on pragmatic evaluation), RHD-INL (RHD impaired on non-literal conditions such as new metaphor and indirect request), RHD-IL (RHD impaired on literal interpretation). The fourth cluster contained only one individual, RHD 7 who was the sole participant impaired on all the tests.

Fig. 3. Dendrogram using Ward's method on the RHD group (15 observations).

A Mann-Whitney non-parametric test performed on the age and educational level of each subgroup revealed that there were neither significant age differences nor significant educational level difference between subgroups (cf. Table 3). A Mann-Whitney non-parametric test performed on post-onset between RHD subgroups also showed no significant differences.

Table 3.

Demographic data, theory of mind and neuropsychological evaluation of the healthy control (HC) group compared to RHD subgroups (RHD-U, RHD-INL and RHD-IL).

HC (n = 15) (mean [SD])

RHD-U (n = 6) (mean [SD])

RHD-INL (n = 3) (mean [SD])

RHD-IL (n = 5) (mean [SD])

Age 60.7 [12.8] 63.5 [9.7] 57.3 [20.6] 58.4 [10.3]

Education 11.7 [3.2] 12.2 [1.2] 9.3 [2.1] 13.0 [4.6]

Theory of mind

Ment-Q (1st order) 75.3 [18.7] 57.5 [16.3] 41.7 [10.4] 53.3 [5.7]

Ment-Q (2nd order) 55.4 [22.7] 39.7 [20.9] 34.3 [5.7] 46.3 [18.5]

Executive functions

Stroop (Colors/words, time in s) 31.2 [10.4] 48.6 [22.4] 49.9 [22.3] 37.6 [9.0]

HC (n = 15) (mean [SD])

RHD-U (n = 6) (mean [SD])

RHD-INL (n = 3) (mean [SD])

RHD-IL (n = 5) (mean [SD])

Stroop (errors) 1.1 [1.1] 1.7 [2.6] 4.0 [1.7] 1.4 [2.1]

Hayling (automatic) 6.5 [0.5] 6.0 [0.6] 5.7 [0.6] 6.0 [1.0]

Hayling (inhibition) 12.2 [1.2] 7.8 [1.9] 7.7 [1.1] 10.2 [2.0]

Trail-making A (time in ms) 38.4 [12.1] 83.8 [42.3] 53.1 [19.2] 93.1 [48.7]

Trail-making B (time in ms) 71.8 [60.6] 200.6 [143.7] 108.0 [12.3] 208.7 [128.1]

WCST (number of categories) 5.0 [1.1] 2.2 [2.2] 3.7 [2.5] 2.0 [0.7]

WCST (number of perseverative errors) 12.9 [11.4] 55.2 [24.3] 24.7 [14.6] 44.0 [17.7]

Fluency 44.4 [13.7] 26.8 [7.0] 20.0 [15.1] 42.4 [10.5]

Digit span forward 10.1 [1.8] 9.5 [2.3] 8.0 [2.0] 8.4 [1.5]

Digit span backward 6.3 [1.7] 4.7 [1.9] 4.7 [2.1] 5.4 [1.9]

Full-size table

RHD-U: RHD participants unimpaired on pragmatic evaluation; RHD-INL: RHD participants impaired on non-literal conditions such as new metaphor and indirect request; RHD-IL: RHD participants impaired on the literal interpretation condition.

Due to the small number of participants in each subgroup, Mann-Whitney non-parametric tests were conducted on subjects' performance on pragmatic, ToM-1st order and ToM-2nd order and neuropsychological tests in order to compare RHD subgroups to HC group (cf. Fig. 4 & Table3). To lighten presentation of the statistical analyses, in this part, only significant results (p < 0.01) will be presented according to each profile.

Fig. 4. Results of pragmatic evaluation for all RHD subgroups and the HC group.

3.4.1. RHD-U profile

This subgroup contained six RHD participants (RHD 6, 10, 5, 1, 3, 9) who performed as the HC group on pragmatic evaluation and on Ment-Q of 1st and 2nd order. However, they performed significantly worse than the HC group on inhibition (Hayling-inhibition: U = 0; p < 0.0001) and flexibility (Trail B: U = 14; p < 0.01; WCST-category: U = 12.5; p < 0.01, WCST-perseverative errors: U = 8; p < 0.01).

3.4.2. RHD-INL profile

This subgroup contained three RHD participants (RHD 4, 8, 13) who performed worse than the HC group on pragmatic evaluation. More precisely, they did significantly worse than HC participants on new metaphor understanding (U = 0; p < 0.01), on indirect request (U = 4.5; p < 0.01) and marginally significantly on idiomatic metaphor (U = 5.5; p = 0.039). These differences in performances between new metaphor and idiomatic metaphor were concordant with studies suggesting that new metaphors rely more on right hemisphere, whereas idiomatic or conventional metaphors rely more on left hemisphere ([Eviatar and Just, 2006], [Giora, 1997] and [Mashal et al., 2007]).

By comparison to the HC group, this pattern of pragmatic performances, co-occurred with difficulty to answer Ment-Q of 1st order (U = 2; p < 0.01); and difficulty with inhibition tests (Stroop-Error: U = 2, p < 0.01; Hayling-inh: U = 0; p < 0.01).

In summary, a co-occurrence of difficulty in understanding non-literal conditions of pragmatic language (indirect requests and new metaphors) in attributing mental states of 1st order and a lack of inhibition seemed to characterize this RHD-INL subgroup.

3.4.3. RHD-IL profile

This subgroup contained five RHD participants (RHD 11, 15, 2, 12, 14) who performed significantly worse than the HC group in understanding literal interpretation in the indirect request task (U = 0; p < 0.0001), whereas they were similar to HC participants on metaphor and indirect request understanding. This pattern of performance co-occurred with a lack of flexibility. Indeed, RHD-IL participants did worse than HC participants on WCST-cat (U = 1; p < 0.0001) and WCST-pers (U = 4; p < 0.01). Marginally significant differences were also found between RHD-IL participants and HC participants on Trail B (U = 14; p = 0.04) and Ment-Q of 1st order (U = 5; p = 0.047). No differences were found between RHD subgroups and the HC group on memory.

To sum up, a co-occurrence of difficulty in the interpretation of literal sentences, in attributing mental states of 1st order and a lack of flexibility seemed to characterize this RHD-IL subgroup.

4. Discussion

This study raised questions concerning whether and to what extent pragmatic deficits in RHD individuals co-occur with other deficits such as ToM limitations and/or executive dysfunction. Fifteen RHD individuals and 15 healthy controls were tested on their pragmatic abilities, theory of mind abilities, and executive functions. The main results confirmed that not all RHD participants had difficulties processing non-literal language or attributing and understanding mental states (ToM), as some of them were able to do pragmatic tests as well as the control group. Such heterogeneous patterns of performance are in line with the known heterogeneity of deficits found after a right-hemisphere lesion ([Champagne et al., 2002] and [Ct et al., 2007]). Three patterns of pragmatic performance were found across the RHD group. The RHD-U subgroup comprised patients who were unimpaired on pragmatic evaluation. The RHD-INL subgroup contained RHD patients who were impaired on non-literal conditions such as new metaphors and indirect requests, while the RHD-IL subgroup contained RHD patients who were impaired only on the literal interpretation condition.

Neither age nor education of RHD participants allowed to account for such different patterns of performance. However, the association of ToM deficits and executive dysfunctions seemed to differentiate the RHD subgroups according to whether or not they presented a deficit in understanding pragmatic aspects of language.

4.1. Co-occurrence of pragmatic and ToM deficits

There seemed to be an association between a deficit in attributing intention to others (ToM) and deficits in understanding pragmatic aspects of language. This result was congruent with other studies that have found a relationship between ToM and pragmatics in individuals with right-hemisphere lesions, autism and traumatic brain injury ([Happ, 1993], [Winner et al., 1998] and [Winner and Leekam, 1991]). Indeed, the RHD-U subgroup was not impaired on pragmatic or ToM evaluation while the other two RHD subgroups were impaired on both pragmatic and ToM abilities. These results confirm the hypothesis that pragmatic interpretation is a mind-reading exercise involving inferences concerning the speaker's mental state (Grice, 1969). The speaker's

intention plays a specific role in understanding pragmatic aspects of language, particularly in the comprehension of irony and indirect requests. It should be noticed that no difference was found between each subgroup and the HC group on 2nd order ToM. This was probably due to the difficulty and complexity of 2nd order ToM and to the small number of participants in each subgroup.

However, a new finding relates to the two types of pragmatic deficits found and the possible associations with different ToM deficits. Indeed, the RHD-INL and RHD-IL subgroups differed with regard to how their impairment affected the pragmatic aspects of language understanding. The RHD-INL subgroup showed deficits affecting the understanding of non-literal language including metaphors and indirect requests, while the RHD-IL subgroup showed deficits only on literal sentence interpretation. This difference may have been due to the fact that the RHD-INL subgroup did not understand mental states, whereas the RHD-IL subgroup over attributed intentions. This hypothesis agrees with the model of Abu-Akel (2003) describing different types of impairment of this ability to attribute mental states. According to Abu-Akel (2003), an impairment of the ability to attribute mental states must be characterized: by a lack of understanding of mental states (someone with no theory of mind would predict behavior on the basis of the actual state of the world rather than of beliefs); by an understanding of mental states, but with abnormal attribution of such states (someone who over attributes knowledge and mental states to others would predict behavior on the basis of wrong beliefs); or by an intact understanding of other people's minds, but with impaired understanding of one's own mind. The ToM performances of the RHD-INL subgroup appear to correspond to the first impairment type reported by Abu-Akel (2003), while performances of the RHD-IL seems to coincide with the second impairment type. However, this hypothesis remains to be confirmed in further research with other tasks assessing pragmatic abilities since results concerning literal interpretation might also be due to the task itself.

This co-occurrence of pragmatic deficits and ToM deficits in RHD individuals also supports the claim that RH-dependent mechanisms seem to be particularly involved in these two processes ([Gallagher et al., 2000] and [Shamay-Tsoory et al., 2005]). For instance, Gallagher et al. (2000) showed in their fMRI study, that the medial prefrontal cortex, known to be involved in ToM tasks, was activated in metaphor comprehension tasks. Evidence from neuroimaging and neuropsychological investigations has led researchers to conclude that ToM is subserved by dedicated brain systems, including the amygdala, temporoparietal junction, superior temporal sulcus, right orbito-frontal cortex and, in particular, the medial frontal lobes ([Rowe et al., 2001], [Saxe and Wexler, 2005], [Siegal and Varley, 2002], [Stone et al., 1998] and [Stuss et al., 2001]). However, our patients' lesion site data did not allow to draw any conclusions concerning the brain regions implicated. Our results only tell us that RHD patients with temporoparietal lesions performed like healthy controls on pragmatic and ToM tasks while patients with right frontal and internal capsule lesions presented pragmatic and ToM deficits of different natures. While Saxe and Wexler (2005) showed that the right temporoparietal junction was recruited selectively for the attribution of mental states, it is possible, however, that lesions in the temporoparietal area of our RHD patients do not affect the temporoparietal junction.

4.2. Co-occurrence of pragmatic/ToM deficits and executive dysfunctions

Two different patterns of executive dysfunction seemed to distinguish the two RHD subgroups which presented pragmatic deficits (RHD-INL, RHD-IL). A deficit in non-literal language understanding co-occurred with a lack of inhibition in the RHD-INL subgroup while a deficit in direct request understanding co-occurred with a lack of flexibility in the RHD-IL subgroup. Each pattern of performance was also associated with a ToM deficit. Until now, there has been no clear answer as to the relationship between the ability to understand second-order mental states or pragmatic aspects of language and executive function. The literature remains contradictory, with some studies showing an association between pragmatic or ToM performance and executive function ([Channon and Watts, 2003] and [Griffin et al., 2006]), whereas others, in different populations, did not ([Martin and McDonald, 2005] and [Rowe et al., 2001]). Our study supports earlier studies that found executive dysfunction to co-occur with pragmatic or ToM deficits, but with no relationship between them, since the RHD-U subgroup exhibited executive dysfunction without pragmatic deficits ([Martin and McDonald, 2005] and [Rowe et al., 2001]). Martin and McDonald (2005), for example, found traumatic brain injury patients to have reduced flexibility. However, this lack of flexibility was not significantly associated with their ability to distinguish irony from deceit.

Finally, our results suggest that lack of inhibition or lack of flexibility alone was not able to account for pragmatic deficits. As Mitchell, Saltmarsh, and Russell (1997) found in children with autism, our study suggests that ToM plays a role above and beyond that of executive function in pragmatic interpretation. An association of ToM deficits and executive dysfunction, rather than executive dysfunction alone, might better account for pragmatic deficits in RHD patients.

5. Conclusion

In conclusion, this study showed that RHD individuals may exhibit different patterns of executive dysfunction (lack of inhibition versus lack of flexibility), which co-occurred with different patterns of pragmatic impairments (metaphor and non-literal interpretation such as indirect request versus literal interpretation) concomitant with a ToM deficit. However, although the executive function model has been suggested to be valid, because it may be the only model of pragmatic deficits that can account for heterogeneous verbal behavior in patients (Martin & McDonald, 2003), our study found that executive dysfunction cannot be the sole cause of RHD subjects' pragmatic deficits. More interestingly, as is postulated to be the case with schizophrenic patients (Brune & Bodenstein, 2005), the association of ToM deficits with executive dysfunction, tapping into inhibition versus flexibility rather than executive dysfunction alone, might be the best predictor of the different patterns of pragmatic deficits, such as non-literal language understanding and literal interpretation of sentences, found in RHD patients.

The hypothesis that differences in ToM deficits can account for metaphor and indirect request understanding versus literal interpretation needs to be confirmed by further research using different tasks. The question of the relationship between pragmatic abilities, ToM and executive functions must be assessed in greater depth by testing more RHD individuals in an attempt to reproduce the performance patterns observed in the current study.

Acknowledgments

This study was made possible by financial support from the Heart and Stroke Foundation of Canada, the Canadian Institutes of Health Research, the Canadian Stroke Network and Astra-Zeneca for MC and from the Canadian Institutes of Health Research (Grant # MT-15006) for YJ. This study was also made possible with the cooperation of the patients recruited for this study, and the support of speech language pathologists: Annie Delyfer, Danielle Fort, Julie Klein and Rene Boisclair-Papillon. Special thanks to Hlne Ct for her help in patient recruitment and for introducing MC to different rehabilitation hospitals in Montreal.

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Sample stimuli for indirect request task (MEC, Joanette et al., 2004)

Story inducing non-literal interpretation: indirect request

Jean est dans sa chambre et coute de la musique. Son pre lui dit: Jean, la porte de chambre est ouverte/Jean is in his room listening to music. His father tells him: Jean, your bedroom door is open.

Question: D'aprs vous, que veut dire son pre?/In your opinion, what does the father mean?

Story inducing literal interpretation

Monsieur Lavoie est au salon lorsque le tlphone se met sonner. Il dit sa femme: je le prends/Mr. Lavoie is in the living room when the phone rings. He says to his wife: I'll take it.

Question: D'aprs vous, que veut dire Monsieur Lavoie?/In your opinion, what does Mr. Lavoie mean?

Sample stimuli for the ToM task

First-order ToM

For the Halloween party, Marie disguises herself as a witch with a dress and a black pointy hat. She meets her friend Isabelle and takes her hat off so Isabelle will recognize her. A child dressed as a ghost appears behind Marie where Marie can't see him. Isabelle screams in terror. Marie then tells her, Don't worry, it's me, Marie.

Ment-Q: Why does Marie say this to Isabelle?

Scoring example: Because she believes that Isabelle is afraid of her (2 pts); because she thinks that Isabelle does not recognize her (1pt).

Fact-Q: What is Marie dressed as?

Inf-Q: Why is Isabelle screaming?

Second-order ToM

Paul has invited Simon to play at his home. Simon is clumsy. He often breaks his friends' toys. They go to Paul's bedroom. A truck is broken, but Paul does not know it. When Paul picks up the truck, Simon says, It wasn't me who broke the truck.

Ment-Q: Why does Simon say this to Paul?

Scoring example: Because he thinks that Paul believes he has broken the truck (2 pts); because they know that when Simon is here, he always breaks toys (1pt).

Fact-Q: Which child is clumsy?

Inf-Q: Whose toys are they?

Corresponding author. Pavillon Albert-Prvost, Hpital du Sacr-Cur de Montral,

6555 Gouin Boulevard West, Montreal, Quebec, Canada H4K 1B3. Tel.: +1 514 338 2222x4415. 1 In the inhibition condition of the Hayling test, participants were asked to complete predictable sentences (Most cats see very well at) with a word that fills the gap, does not make sense and is unrelated to the expected ending.