Patients with psychosis struggle with scalar implicatures
Introduction
Successful social interactions rely heavily on one's ability to go beyond the explicit, literal content of conversational statements and grasp the actual, intended meaning for in daily communication, the message that one wants to express is often not explicitly mentioned. For decades, researchers have illustrated the difficulties patients diagnosed with psychosis experience when they have to decode the non-literal content of conversational statements. These difficulties include trouble grasping the figurative meaning of proverbs and metaphors and problems with understanding humor and irony (e.g., Bambini et al., 2016; Brüne and Bodenstein, 2005; Sponheim et al., 2003). Langdon et al. (2002b) showed for instance that patients with psychosis made more errors than controls in a story comprehension task, when the speech was metaphorical or ironic. More broadly, Linscott (2005) demonstrated that such patients were less compliant with Gricean conversational rules. A broad assessment of the pragmatic skills of patients with psychosis, using the Assessment Battery of Communication, showed that the impairments in patients with psychosis is extended to many domains of communicative skills (Colle et al., 2013). It's important to note that even when syntax and semantics are more or less intact, people with psychosis sometimes still show difficulties at the discourse level (e.g., Andreasen et al., 1985; Frith and Allen, 1988).
Although pragmatic language has been studied extensively in the context of psychosis, one of the most studied types of pragmatic inferences namely scalar implicatures (SIs) (Guasti et al., 2005; Papafragou and Musolino, 2003), to the best of our knowledge, have not yet been studied in people with psychosis. In the present study, we therefore aim to gain insight in the ability of people with psychosis to derive SIs. We believe that the study of scalar stimuli in the context of psychosis has the potential to advance our understanding of the mechanisms underlying pragmatic language deficit in patients with psychosis. Scalar stimuli allow a high level of control over both stimulus content and context, which may be problematic in more complex language stimuli like stories or in stimuli with fixed content like proverbs. This high level of manipulability of scalar stimuli creates new ways to study the influence of minor stimulus changes on pragmatic language comprehension.
SIs are based on linguistic expressions like some, or, must etc. Such expressions are part of a scale of informativeness that is ordered from less informative to more informative. Examples of such scales are: < Some/many/all >, < May/must >, < Sometimes/often/always >.
The statement
- (1)
Some patients were attentive will be generally interpreted as
- (2)
Some but not all patients were attentive
And not as
- (3)
All patients were attentive.
However, on a strictly semantic level “some” means “some and possibly all”. The (implicit) addition of “but not all” does not follow logically but is the result of a SI. These SIs occur because interlocutors regard human conversation as a cooperative process, guided by a number of communicative principles or maxims (Grice, 1975). One of these maxims, the maxim of quantity, requires utterances to provide no more and no less information than is necessary for the purpose and clarity of the conversation. This maxim underlies the SI above. A sentence like (1) might be considered underinformative: it's not clear whether or not all patients were attentive. The speaker thus seems to violate the maxim of quantity. But since the receiver/listener assumes the speaker to be cooperative and to obey the maxim of quantity, he infers that the speaker used the weaker “some” because the stronger “all” was not applicable. He therefore derives a SI and concludes that “some but not all” patients were attentive.
According to Nieuwland et al. (2010), people with pragmatic language difficulties, would be less sensitive to violations of the conversational maxims and hence less likely to derive pragmatic inferences including SIs. Based on data about pragmatic language difficulties in people with psychosis, we hypothesize that people with psychosis will be less prone to derive SIs. However, we don't want to make too strong a claim, because not all work on scalar expressions in clinical populations points in this direction. For instance, Chevallier et al. (2010) reported no significant differences in the number of pragmatic responses on the disjunction (interpreting “or” as “A or B, but not both”, instead of the logical “A or B or both) between children with and without autism spectrum disorders (ASD).
In the present study, we test how people with psychosis respond to underinformative statements containing “some”. We expect patients with psychosis to have problems deriving SIs: they will respond less pragmatically when confronted with the scalar expression “some” than controls.
Section snippets
Participants
Two groups of participants took part in the study. The patient group consisted of 25 adults diagnosed with schizophrenia according to DSM-IV by an experienced psychiatrist. All patients were outpatients. The second group, the control group, was matched to the patient group with respect to age and educational level (see Table 1). All participants were of Dutch literacy and provided written informed consent.
Procedure and study material
We used a binary statement-evaluation-task. Each participant received one of two
Participants
The patient group consisted of 17 young psychotic patients between 16 and 31 years old, who were diagnosed with psychosis according to DSM-IV by an experienced psychiatrist. The large majority of patients were male and all but two patients were hospitalized. The control group was matched to the patient group based on age and educational level (Table 3).
Study material
We used the same two stimulus sets as in Experiment 1 but now participants had to judge the truthfulness of the statements on a 3-point scale
General discussion and conclusion
To the best of our knowledge, the present study is the first one to address SIs in the context of psychosis. Based on the literature about pragmatic language difficulties in patients with psychosis, we hypothesized that these patients would be less likely to derive SIs than controls.
Our results confirmed this hypothesis: patients with psychosis derived fewer SIs than matched control subjects. In general, patients seem to prefer the logical interpretation of semantic expressions like “some” to
Contributors
Martien Wampers and Walter Schaeken designed the study and wrote the study protocol. Martien Wampers, Sofie Schrauwen, Marc De Hert and Leen Gielen were responsible for the recruitment and testing of participants. Martien Wampers, and Sofie Schrauwen performed the statistical analyses. Martien Wampers wrote the first draft of the manuscript and all other authors contributed to and have approved the final manuscript.
Funding body agreements and policies
Not applicable.
Conflict of interest
None of the authors has any conflict of interest to disclose.
Acknowledgements
We would like to thank the entire staff of Sint-Joris, the ward for young people with psychosis of the University Psychiatric Centre KU Leuven, for their support during the data collection process.
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