Motivations Language has evolved as human’s primary communication tool. It allows us to flexibly manage the amount of information disclosed in communication to deal with complex social situations. Language impairment is a hallmark feature of schizophrenia, which could also be observed to a lesser extent in patients’ unaffected siblings. It significantly affects patients’ social functioning and clinical outcome. Despite ample evidence showing deficits across linguistic levels in schizophrenia, our understanding of patients’ performance in real-life communication, especially under non-cooperative (competitive or tactical) situations, is very limited. In this study we developed a novel method (conversational analysis paradigm, CAP) to investigate both cooperative and competitive communication performance in terms of verbal information value management among patients with schizophrenia and their unaffected siblings compared with healthy controls, and explored their relationships with clinical and cognitive functions. Methods Two studies were conducted. Study one consisted of a validation study (n=40) for CAP and a cross-sectional (n=130) study in investigating verbal information management in schizophrenia and healthy participants. Performance was compared between patients with schizophrenia spectrum disorders (n=65) and matched healthy controls (n=65). Relationships between cognitive functions, clinical features, social competence, and CAP performance were also investigated. In study two, CAP performances were compared among 31 pairs of patients with schizophrenia, their healthy siblings and 31 matched healthy controls (total n=93) to examine verbal information management deficits as a trait in siblings. Schizotypal personality trait was also measured to investigate the potential relationship with CAP in siblings and healthy controls. Results The CAP test demonstrated good inter-rater reliability (ICC 0.82) and adequate internal consistency (Cronbach’s alpha 0.71--‐0.72). Patients showed poorer performance in verbal information management under both cooperative and competitive conditions, which were associated with psychotic symptoms and social functioning. Patients’ poorer cooperatively communicating information, but not competitive controlling information, was associated with their cognitive functions. Performance of patients’ healthy siblings was intermediate between patients and healthy controls, especially during competitive communication. Verbal information management skills were correlated with schizotypal personality trait in siblings but not controls. More deviant verbal information management skills under competitive conditions were closely related to impaired immediate social network in patients and siblings. Discussion This study empirically documented the impaired verbal information management tactics in patients with schizophrenia and their healthy siblings compared using CAP. This specific domain of language impairment was related with cognitive functions, psychotic symptoms, real-life functioning, and schizotypal personality trait. Significance The current study has taken the first attempt to demonstrate an impairment of verbal information transfer in schizophrenia using a newly developed ecological test. Results of this study laid the groundwork for understanding language impairments related to schizophrenia, suggesting verbal information management as a candidate endophenotype of schizophrenia with intervention implications. / published_or_final_version / Psychiatry / Doctoral / Doctor of Philosophy