Piecing together fragments: Linguistic cohesion mediates the relationship between executive function and metacognition in schizophrenia

Abstract

Speech disturbances are prevalent in psychosis. These may arise in part from executive function impairment, as research suggests that inhibition and monitoring are associated with production of cohesive discourse. However, it is not yet understood how linguistic and executive function impairments in psychosis interact with disrupted metacognition, or deficits in the ability to integrate information to form a complex sense of oneself and others and use that synthesis to respond to psychosocial challenges. Whereas discourse studies have historically employed manual hand-coding techniques, automated computational tools can characterize deep semantic structures that may be closely linked with metacognition. In the present study, we examined whether higher executive functioning promotes metacognition by way of altering linguistic cohesion. Ninety-four individuals with schizophrenia-spectrum disorders provided illness narratives and completed an executive function task battery (Delis-Kaplan Executive Function System). We assessed the narratives for linguistic cohesion (Coh-Metrix 3.0) and metacognitive capacity (Metacognition Assessment Scale – Abbreviated). Selected linguistic indices measured the frequency of connections between causal and intentional content (deep cohesion), word and theme overlap (referential cohesion), and unique word usage (lexical diversity). In path analyses using bootstrapped confidence intervals, we found that deep cohesion and lexical diversity independently mediated the relationship between executive functioning and metacognitive capacity. Findings suggest that executive control abilities support integration of mental experiences by way of increasing causal, goal-driven speech and word expression in individuals with schizophrenia. Metacognitive-based therapeutic interventions for psychosis may promote insight and recovery in part by scaffolding use of language that links ideas together.

Introduction

A cardinal feature of psychosis described by Bleuler (1911) in coining the term “schizophrenia” is a loosening of associations evident in fragmentation of language, thought, and behavior. Language disturbances such as tangentiality, derailment, and illogical speech, often categorized as thought disorder (Andreasen, 1979), have been documented in chronic schizophrenia (Barch and Berenbaum, 1996), early-stage psychosis (Minor et al., 2016), and those at clinical-risk for psychosis (Bearden et al., 2000; Elvevåg et al., 2010). These findings indicate that language disturbances are not purely a function of illness severity and occur across stages of psychosis. Some evidence suggests that impaired executive functioning common to psychotic illness (Heinrichs and Zakzanis, 1998) may hinder the production of cohesive discourse (Kerns and Berenbaum, 2002).

Less is known about how these observable language disturbances relate to interruptions in the ability to synthesize mental experiences and make sense of one's life and challenges. This set of psychological processes, referred to as metacognition, involves an awareness of one's own thoughts and desires and beliefs about other people's mental experiences (Flavell, 1979; Semerari et al., 2003). Metacognitive impairment may be a fundamental source of the disruptive symptoms in psychotic illness (Lysaker and Klion, 2017). Individuals with compromised metacognitive capacity may perceive their thoughts to be disjointed and the actions of others to be random, manifesting in a disorienting existence devoid of agency. Lower metacognitive capacity in psychosis has been associated with greater concurrent and prospective negative symptoms (Hamm et al., 2012), higher levels of anhedonia (Buck et al., 2014), lower levels of functional competence (Lysaker et al., 2011), and a more sedentary lifestyle (Snethen et al., 2014). While the etiology of metacognitive deficits is multifaceted, one potential source is impaired executive functioning. If one is unable to fluidly shift their attention, monitor thoughts and actions, and inhibit inappropriate or irrelevant behaviors, piecing together complex information to form a coherent sense of self may be challenging. Research suggests that executive function deficits may contribute to impairments in metacognition (Lysaker et al., 2008) and related abilities of perspective-taking (Long et al., 2018; Wardlow, 2013) and theory of mind (Wade et al., 2018). However, researchers have yet to examine whether impaired executive function leads to metacognitive deficits in psychosis by way of producing fragmented speech.

One explanation for this knowledge gap is that discourse studies have historically used manual hand-coding systems that are unable to characterize deeper semantic structures. Recent technological advances offer new ways to measure the relationship between language disturbances and metacognition in psychosis. In particular, computational linguistic approaches enable objective and comprehensive depictions of underlying syntactic and semantic cohesion (Cabana et al., 2011; Cohen and Elvevåg, 2014). Studies employing Latent Semantic Analysis (Landauer and Dumais, 1997) and graph theoretic techniques (De Deyne et al., 2013, De Deyne et al., 2016) have found decreased semantic coherence (Elvevåg et al., 2007) and connectedness (Mota et al., 2017) in the discourse of individuals with psychosis relative to healthy individuals. Automatic classification analyses using linguistic indices have accurately distinguished discourse between individuals with schizophrenia and controls (Corcoran et al., 2018; Elvevåg et al., 2007; Mota et al., 2017; Strous et al., 2009; Willits et al., 2018), unaffected first-degree relatives (Elvevåg et al., 2010), and individuals experiencing mania (Mota et al., 2012). Computational linguistic approaches have also accurately predicted psychosis onset (Bedi et al., 2015; Corcoran et al., 2018) as well as explained greater variance and predicted diagnosis better than clinician-rated scales (Minor et al., 2019; Mota et al., 2012). Fine-grained characterization of discourse via automated techniques may aid in revealing semantic structures related to disordered thought and integration of complex information in psychosis.

Computational tool Coh-Metrix (McNamara et al., 2014) produces an array of indices that measure complex discourse structures. One Coh-Metrix study found decreased deep cohesion, or causal and goal-driven connecting phrases, in individuals with schizophrenia compared to an adversity-matched comparison group of HIV positive individuals (Willits et al., 2018). This supports findings of an impaired sense of agency in psychosis (Jeannerod, 2009; Synofzik et al., 2010) given that deep cohesion in part measures one's connections between intentional events and actions. Discourse analyses have also assessed word and theme overlap as a measure of referential cohesion, thought to aid the reader/listener by repeating parts of speech. A Coh-Metrix study found that individuals at ultra-high risk (UHR) for psychosis had reduced referential cohesion in the form of word stem overlap compared to controls (Gupta et al., 2018), aligning with prior work in thought disorder using hand-coded techniques (Harvey, 1983). This reduction in referential cohesion correlated with higher psychotic symptoms and lower verbal learning in the UHR group. Studies have also found reduced lexical diversity, or usage of unique words, in the discourse of individuals with thought disorder compared to controls and patients without thought disorder (Manschreck et al., 1981, Manschreck et al., 1984). Interestingly, however, referential cohesion and lexical diversity are inversely related (McNamara et al., 2014). A potential explanation for findings of impairments in both indices in psychosis across studies is that word repetition due to thought-disordered perseveration may impede effective communication, whereas intentional lexical repetition aids in connecting relevant threads for the listener (Crider, 1997). Collectively, these findings catalyzed our investigation as to whether particular discourse structure abnormalities in psychosis hinder one's ability to integrate thoughts and affect.

In the present study, we assessed the relationship between metacognition, executive function, and linguistic cohesion in individuals with schizophrenia-spectrum disorders. We measured metacognition using the Metacognition Assessment Scale – Abbreviated (MAS-A; Lysaker and Klion, 2017; Lysaker et al., 2019) based on narratives from the Indiana Psychiatric Illness Interview (IPII; Lysaker et al., 2002). We used the Delis-Kaplan Executive Function System (D-KEFS; Delis et al., 2001) to measure executive function and formed sub-components of inhibition, monitoring, and conceptual flexibility (Hecht and Latzman, 2018; Latzman and Markon, 2010). We analyzed linguistic cohesion in the rich discourse sample provided by the IPII with the Coh-Metrix tool (McNamara et al., 2014). Based on prior research outlined above, we selected three linguistic indices that measure logical and intentional connections within speech (deep cohesion), content overlap (referential cohesion), and unique word usage (lexical diversity). For data analysis, we performed correlations followed by path analyses to test whether linguistic cohesion mediated the relationship between executive function and metacognition.

Our central hypothesis was that higher executive function promotes greater metacognitive capacity through altering linguistic cohesion. In other words, we predicted that greater abilities to shift, inhibit, and monitor behavior enable the production of coherent discourse, which in turn supports the integration of complex information about oneself, others, and the world. This prediction is supported in part by evidence suggesting that executive functioning is associated with the ability to form organized and coherent narratives. A meta-analysis examining cognitive impairments in schizophrenia found consistent positive associations between thought disorder and executive function, particularly the abilities to inhibit and maintain goal-relevant content in memory (Kerns and Berenbaum, 2002). Executive function deficits may be particularly related to disjointed speech rather than incorrect language usage in general. This idea is supported by findings that impaired ability to sequence information in individuals with schizophrenia predicted failures to make explicit connections between words or phrases but not the frequency of incorrect or unclear wording (Docherty et al., 2006). Some researchers have posited that reduced working memory capacity in psychosis may lead to distinct types of speech disturbances in different individuals. For example, one study found an inverse relationship between reduced speech production and discourse abnormalities such as tangentiality and derailment in schizophrenia (Barch and Berenbaum, 1997). The authors theorized that reduced working memory resources could either lead an individual to produce less speech yet maintain coherence, or produce more speech but fail to monitor speech content. Developmental evidence in children suggests that the abilities to structure coherent narratives and utilize executive functions support one another over time. In particular, one study found that formation of organized narratives predicted future response inhibition and was predicted by prior attentional capacity (Friend and Bates, 2014). In sum, these findings suggest that capacities to flexibly monitor, inhibit, and update one's thoughts and actions to accomplish tasks promote the maintenance and planning of effective communication.

Additional support for our hypothesis includes preliminary findings that executive function and linguistic cohesion predict metacognitive abilities. One study found that the metacognitive capacity to reflect upon one's own thoughts positively correlated with mental flexibility, whereas awareness of others' thoughts correlated with inhibition (Lysaker et al., 2008). Other studies found positive associations between working memory, inhibition, and switching with perspective-taking, an important facet of metacognition that allows one to distinguish between one's own thoughts and the thoughts of others (Long et al., 2018; Wardlow, 2013). Lastly, studies have found that lexical measures indicative of thought complexity predicted overall metacognitive capacity (Buck et al., 2015; Minor et al., 2019). Overall, we sought to examine whether abilities to flexibly monitor and inhibit behavior (i.e., executive function) support the capacity to derive meaning from mental experiences (i.e., metacognition) by way of increasing coherent speech (i.e., linguistic cohesion) in schizophrenia.