Impaired Probabilistic Learning deficits in Schizophrenia: A study with Motor Execution and Imagery

Schizophrenia is associated with cognitive impairments, including deficits in implicit learning. Probabilistic serial reaction time tasks (SRTT) offer an objective approach to characterizing these deficits through both motor execution (ME) and motor imagery (MI), the mental simulation of movement without physical action. Whether implicit probabilistic sequence learning is impaired across both modalities in schizophrenia remains poorly understood. Thirty individuals with schizophrenia (ME: n=12; MI: n=13) and 40 healthy controls (ME: n=20; MI: n=20) completed an auditory probabilistic SRTT. Symptom severity was assessed with the PANSS and cognitive functioning with the MCCB. Healthy controls demonstrated a robust signature of implicit probabilistic sequence learning, whereas participants with schizophrenia exhibited weaker and less consistent learning signatures, particularly during motor imagery. Sensitivity to probabilistic structure differed significantly between groups during motor execution but not motor imagery. Participants with schizophrenia also showed significantly longer reaction times than controls across both modalities, consistent with generalized psychomotor slowing. Greater PANSS-General severity was associated with greater deviation from the probabilistic learning patterns observed in healthy controls during ME, whereas higher MCCB verbal learning scores were associated with greater similarity to these learning patterns during MI. These findings indicate that implicit probabilistic sequence learning is impaired in schizophrenia across both motor execution and motor imagery, and that these deficits are meaningfully associated with clinical symptom severity and cognitive functioning.