Linguistic markers of schizophrenia: a case study of R obert W alser (2024)

Abstract: We present a study of the linguistic output of the German-speaking writer Robert Walser using NLP. We curated a corpus comprising texts written by Walser during periods of sound health, and writings from the year before his hospitalization, and writings from the first year of his stay in a psychiatric clinic, all likely at- tributed to schizophrenia. Within this corpus, we identified and analyzed a total of 20 lin- guistic markers encompassing established met- rics for lexical diversity, semantic similarity, and syntactic complexity. Additionally, we ex- plored lesser-known markers such as lexical innovation, concreteness, and imageability. No- tably, we introduced two additional markers for phonological similarity for the first time within this context. Our findings reveal sig- nificant temporal dynamics in these markers closely associated with Walser’s contempora- neous diagnosis of schizophrenia. Furthermore, we investigated the relationship between these markers, leveraging them for classification of the schizophrenic episode.

## introduction schizophrenia is a heterogeneous psychiatric disorder characterized by diverse symptoms impacting a person's perception, cognition, language and motor functions. the disorder displays variable courses; some patients undergo circumscribed episodes with psychotic symptoms and either complete or incomplete remission, while others follow a chronic course with persistent symptoms at a relatively stable level. typically, there is a prodromal period, ranging from several weeks to several years, that precedes the first psychotic episode. symptoms in schizophrenia can be broadly categorized into two groups: positive symptoms, such as hallucinations, delusions, and certain formal thought disorders like derailment and word salad; and negative symptoms, including poverty of speech, alogia, anhedonia, and social withdrawal @xcite . in clinical psychiatry, the diagnosis of schizophrenia is established based on interviews and diagnostic manuals that provide comprehensive descriptions of symptoms. despite advances in modern medicine, the absence of concrete (bio)markers for diagnosis and individualized treatment for schizophrenia persists. concurrently, patients exhibit fluctuating alterations in language production and comprehension that correlate with the illness's dynamics and severity. despite the long history of study of language in connection to mental illness (the first accounts on recognizable linguistic patterns are indeed older than the term "schizophrenia" and even its predecessor "dementia praecox" @xcite , only the recent advances of computational linguistics and nlp provide the necessary tools and technology to analyze substantial linguistic datasets and extract linguistic features in an objective and replicable manner @xcite . several authors identify the potential of linguistic features extracted by means of nlp as possible biomarkers of psychosis @xcite . @xcite emphasizes that linguistic production not only reflects biological processes but also incorporates social aspects. consequently, he contends that language can be regarded as a biosocial marker. our stance is that schizophrenia (and mental illness in general) should not be oversimplified to mere biology. we view the concept of biomarkers as an analogy, comparable to blood sugar levels or blood pressure in somatic medicine. notably, a significant gap exists in the current state of research, with no established population norms for the nlp features. this contrasts sharply with the majority of biomarkers in traditional medicine. addressing this gap could involve adopting a personalized methodology, observing changes in linguistic output over time in individual subjects. nowadays, nlp methodologies are commonly used to demonstrate significant differences in the linguistic production between participants suffering from schizophrenia or high-risk individuals compared with neurotypical participants. furthermore, it seems that computational linguistic features at least partially correlate with the severity of psychotic symptoms. a promising recent trend in the field is to produce and analyse longitudinal datasets and explore the stability or the dynamics of the linguistics markers within schizophrenia. as schizophrenia is characterized by a highly heterogenous expression of symptoms, it is not surprising that there is evidence of a substantial difference in the linguistic markers within the schizophrenia group @xcite . given the advancements in individualized medicine, an important question arises: can variations in linguistic markers be identified within each individual's language output, enabling a truly personalized method for diagnosing relapses and monitoring the disease? if so, nlp could furnish tools for tailoring individualized detection algorithms, thereby aiding in the prevention of future psychotic episodes. in this study, we adopt such a longitudinal approach using a single-subject design. our study is based on a linguistic corpus comprising short literary texts authored by the german-speaking writer robert walser who probably suffered from schizophrenia. from this corpus, we extracted established linguistic features for lexical diversity and lexical innovation, syntactic complexity, and semantic similarity. additionally, we introduce markers for phonological similarity. we present evidence of significant marker dynamics temporally linked to walser's diagnosis of schizophrenia and subsequent hospitalization. in this work, we contribute to the intersection of nlp and psychiatry through multiple avenues. primarily, we explore various nlp findings at the individual level. furthermore, we introduce a novel linguistic marker, phonological similarity, warranting future investigation. additionally, our utilization of a corpus from a german-speaking writer enhances the linguistic diversity within this domain. ## results statistically significant differences between time periods were observed for the majority of linguistic markers after bonferroni correction ( ## discussion in this study, we analyzed the linguistic production of the german-speaking author robert walser, who probably suffered from schizophrenia, using nlp. walser's case is particularly intriguing, given that he produced a substantial body of literary texts over a period of more than 30 years, and towards its end he was hospitalized in a psychiatric clinic with a diagnosis of schizophrenia. to construct our corpus, we compiled short prose from three distinct timeframes @xcite , the latter coinciding with walser's hospitalization for schizophrenia in january 1929. biographical notes suggest his experience of psychotic symptoms before hospitalization, indicating that the texts from the third period were likely composed during a psychotic state. examining several established nlp features, we investigate their temporal association with walser's psychosis. additionally, we introduce two novel markers which aim at capturing phonological similarity and imagiabil- furthermore, walser's later texts feature a notable decrease in both concreteness and imageability, resulting in a more abstract and ambiguous tone. the high correlation between imageability and concreteness suggests a shared underlying phenomenon. @xcite demonstrate sufficient test-retest reliability for word concreteness over a 6-month period, indicating its stability within that timeframe. our analysis spans a much longer period @xcite , allowing for a comprehensive comparison. to date, only @xcite . reported a null association between social cognition or metacognition and concreteness so that the relationship between these markers and psychopathological symptoms remains to be studied. overall, concreteness and imageability emerge as promising markers warranting further investigation. in our analysis, we introduced a novel measure of phonological similarity, utilizing jaro-winkler similarity for the first time in schizophrenia-related nlp research. specifically, we assessed similarity between a token (as phoneme) and a subsequent window of 10 or 20 tokens, yielding two highly correlated values likely measuring the same phenomenon. in the analysis of semantic coherence yielded contrasting outcomes. with pretrained word2vec embeddings, a significant reduction in semantic similarity for 5-token chunks emerged in the third period, showcasing a moderate effect size. these results align with previous findings @xcite @xcite @xcite . however, semantic similarity for 10-word chunks did not attain significance post-bonferroni correction. notably, these markers exhibited high correlations solely among themselves, distinct from other dataset markers. conversely, utilizing pretrained bert embeddings revealed increased cosine similarity between consecutive sentences in the third period compared to the first period. additionally, 1st and 2nd order coherence exhibited significant positive correlations with measures of syntactic complexity. it seems that in the case of walser the cosine similarity measured from the pretrained bert model could be associated with syntax. interestingly, the correlation between semantic similarity values from word2vec and bert embeddings did not demonstrate significance, suggesting that they capture of distinct underlying phenomena. there were also significant differences in the syntactic features although their effect was much less pronounced compared to the linguistic markers already described. notably we could not find the reduction of syntactic complexity which has been described by @xcite and @xcite . since this reduction of complexity has been associated with depression and negative symptoms, we can speculate that walser was not showing these symptoms at the time before his schizophrenia diagnosis. the observation regarding the lack of significant differences in the use of pronouns in walser's texts is intriguing. this finding seemingly contradicts prior research @xcite @xcite . however, it's important to note that the increased use of 1st person pronouns, associated with schizophrenia, might not exclusively indicate this condition but might be observed across various mental health conditions @xcite . therefore, this particular marker might not hold substantial promise for schizophrenia detection. our findings offer an intriguing perspective on the concept of biomarkers or biosocial markers in schizophrenia. unlike traditional biomarkers in somatic medicine, we observe an individual constellation that may not always align with the typical profile for the disease in the population. for instance, an increase in the usage of personal pronouns, a linguistic feature typically found in schizophrenia, does not manifest in walser's later texts. conversely, we observe a decrease in concreteness and imageability, along with an increase in phonological similarity. considering the pressing demand for markers for schizophrenia in clinical practice, an nlp-driven approach shows promise. its strength lies in its capacity for personalized analysis, identifying individual markers with significant predictive power. utilizing these markers holds potential for predicting relapses and enhancing tailored interventions.