Individuals with schizophrenia, particularly those with passivity symptoms, may not feel in control of their actions, believing them to be controlled by external agents. Cognitive operations that contribute to these symptoms may include abnormal processing in agency as well as body representations that deal with body schema and body image. However, these operations in schizophrenia are not fully understood, and the questions of general versus specific deficits in individuals with different symptom profiles remain unanswered. Using the projected-hand illusion (a digital video version of the rubber-hand illusion) with synchronous and asynchronous stroking (500 ms delay), and a hand laterality judgment task, we assessed sense of agency, body image, and body schema in 53 people with clinically stable schizophrenia (with a current, past, and no history of passivity symptoms) and 48 healthy controls. The results revealed a stable trait in schizophrenia with no difference between clinical subgroups (sense of agency) and some quantitative (specific) differences depending on the passivity symptom profile (body image and body schema). Specifically, a reduced sense of self-agency was a common feature of all clinical subgroups. However, subgroup comparisons showed that individuals with passivity symptoms (both current and past) had significantly greater deficits on tasks assessing body image and body schema, relative to the other groups. In addition, patients with current passivity symptoms failed to demonstrate the normal reduction in body illusion typically seen with a 500 ms delay in visual feedback (asynchronous condition), suggesting internal timing problems. Altogether, the results underscore self-abnormalities in schizophrenia, provide evidence for both trait abnormalities and state changes specific to passivity symptoms, and point to a role for internal timing deficits as a mechanistic explanation for external cues becoming a possible source of self-body input.

The projected hand illusion (PHI) is a variant of the rubber hand illusion (RHI), and both are commonly used to study mechanisms of self-perception. A questionnaire was developed by Longo et al. (2008) to measure qualitative changes in the RHI. Such psychometric analyses have not yet been conducted on the questionnaire for the PHI. The present study is an attempt to validate minor modifications of the questionnaire of Longo et al. to assess the PHI in a community sample (n = 48) and to determine the association with selected demographic (age, sex, years of education), cognitive (Digit Span), and clinical (psychotic-like experiences) variables. Principal components analysis on the questionnaire data extracted four components: Embodiment of "Other" Hand, Disembodiment of Own Hand, Deafference, and Agency-in both synchronous and asynchronous PHI conditions. Questions assessing "Embodiment" and "Agency" loaded onto orthogonal components. Greater illusion ratings were positively associated with being female, being younger, and having higher scores on psychotic-like experiences. There was no association with cognitive performance. Overall, this study confirmed that self-perception as measured with PHI is a multicomponent construct, similar in many respects to the RHI. The main difference lies in the separation of Embodiment and Agency into separate constructs, and this likely reflects the fact that the "live" image of the PHI presents a more realistic picture of the hand and of the stroking movements of the experimenter compared with the RHI.

The sense of agency is an essential part of human experience. One aspect of agency, intentional binding, is the subjective contraction of time between a willful, voluntary action and the sensory consequences of that action. Previous studies of intentional binding have mainly been conducted with undergraduate samples. The present study utilized a 200- to 600-ms interval estimation task, with active and passive movements, to assess intentional binding in a community sample (mean age = 44.6, range = 21–60) in whom psychosis-like experiences (PLE) were also assessed. Intentional binding, assessed with a 200-ms interval between an action and a subsequent tone, was observed in younger, but not older, adults. Independent of age, increasing PLE were associated with increased intentional binding at the 200-ms interval. Participants reported the perceived interval to be greater for active movements in comparison to passive movements (perceptual repulsion) at 400- and 600-ms intervals, independent of age. We found an overall decrease in the perceived length of the interval associated with aging, independent of movement condition, and an overall increase in the length of the perceived interval associated with an increase in PLE, independent of age. We propose that aging decreases, whereas PLE increases, the size of the temporal window in which an action and its consequence/s can be bound. Finally, we propose that increasing age is associated with a slowing down, and PLE with a speeding up, of an internal pacemaker, one that may be regulated by dopaminergic transmission.