Many individuals with Parkinson's disease (PD) are known to have difficulties in understanding pragmatic aspects of language. In the present study, a group of eleven non-demented PD patients and eleven healthy control (HC) participants were tested on their ability to interpret communicative intentions underlying verbal irony and lies, as well as on their ability to infer first- and second-order mental states (i.e., theory of mind). Following Winner et al. (1998), participants answered different types of questions about the events which unfolded in stories which ended in either an ironic statement or a lie. Results showed that PD patients were significantly less accurate than HC participants in assigning second-order beliefs during the story comprehension task, suggesting that the ability to make a second-order mental state attribution declines in PD. The PD patients were also less able to distinguish whether the final statement of a story should be interpreted as a joke or a lie, suggesting a failure in pragmatic interpretation abilities. The implications of frontal lobe dysfunction in PD as a source of difficulties with working memory, mental state attributions, and pragmatic language deficits are discussed in the context of these findings.
Parkinson's disease (PD) is a chronic, neurodegenerative disorder associated with progressive depletion of dopaminergic neurons in the basal ganglia, a set of subcortical structures with extensive connectivity in the brain, particularly to areas of the forebrain (Brown and Marsden, 1998). While idiopathic PD is most commonly recognized by its motor signs, there is now little doubt that many non-motor signs emerge during the progression of the disease (e.g., changes in sensory processing and cognition), although these symptoms tend to vary in nature and severity from one patient to another (Demakis, 2007 and Dubois and Pillon, 1997).
In particular, many PD patients exhibit cognitive impairments which affect organization and planning (‘executive functions’) and/or working memory (Brown and Marsden, 1991, Gabrieli et al., 1996, Lewis et al., 2003 and Taylor et al., 1986). In the majority of PD patients, reductions in executive processing and control occur in the absence of broad intellectual decline or dementia. Similarly, there is evidence that PD patients without dementia experience difficulties which affect the processing of verbal (Angwin et al., 2005, Berg et al., 2003, Grossman et al., 2002, Lieberman et al., 1990, McNamara and Durso, 2003, Monetta and Pell, 2007 and Natsopoulos et al., 1997) and nonverbal language (Dara et al., 2008 and Pell and Leonard, 2003). The negative impact of communication impairments on the social and functional independence of individuals living with PD is beginning to be documented (Pell et al., 2006 and Pitcairn et al., 1990).
It is of special interest here that certain language abilities, such as those which rely on pragmatic knowledge and awareness, are believed to be highly dependent on intact cognitive resources during language processing tasks (McDonald and Pearce, 1998 and Stemmer et al., 1994). Pragmatics is a general term that refers to the use of language in context, including both physical context and aspects such as speaker intentions, mood, and the emotional state of the speaker; as such, pragmatic processing reflects instances where the capacity to communicate rests not only on an intact language system but also on the knowledge of a specific communicative exchange context and high-level capacities (Martin and McDonald, 2003). Pragmatic language functions include the ability to generate appropriate inferences from linguistic material, to interpret metaphorical and nonliteral language (e.g., indirect speech acts, humor), and to interpret language in the context of paralinguistic, nonverbal, and situational cues which inform intended meanings.
A strong link has been made between the ability to understand “complex” and pragmatic forms of language and the individual cognitive resource capacity of patients with PD (Grossman et al., 2003, Monetta and Pell, 2007 and Monetta et al., 2008b). In a recent study, Monetta and Pell (2007) investigated how participant groups with and without PD processed metaphorical versus literal meanings of language using a timed property verification task (Gernsbacher et al., 2001). They noted a selective decline in the ability to understand more cognitively demanding metaphorical meanings in individual PD patients with impaired working memory capacity when compared to PD patients with working memory scores in the control group range. The ability to generate inferences during story comprehension was also predicted by the working memory capacity of individual PD patients in another recent study (Monetta et al., 2008b). Other researchers have linked deficits in complex sentence processing in PD to underlying reductions in the rate of information processing or strategic allocation of attention (Grossman et al., 2002 and Lee et al., 2003). Collectively, these findings argue for additional studies to look at the impact of PD on pragmatic language processing relative to the cognitive resource capacity of individual PD patients.
