Temporal event structure and timing in schizophrenia: preserved binding in a longer "now"

Patients with schizophrenia experience a loss of temporal continuity or subjective fragmentation along the temporal dimension. Here, we develop the hypothesis that impaired temporal awareness results from a perturbed structuring of events in time-i.e., canonical neural dynamics. To address this, 26 patients and their matched controls took part in two psychophysical studies using desynchronized audiovisual speech. Two tasks were used and compared: first, an identification task testing for multisensory binding impairments in which participants reported what they heard while looking at a speaker's face; in a second task, we tested the perceived simultaneity of the same audiovisual speech stimuli. In both tasks, we used McGurk fusion and combination that are classic ecologically valid multisensory illusions. First, and contrary to previous reports, our results show that patients do not significantly differ from controls in their rate of illusory reports. Second, the illusory reports of patients in the identification task were more sensitive to audiovisual speech desynchronies than those of controls. Third, and surprisingly, patients considered audiovisual speech to be synchronized for longer delays than controls. As such, the temporal tolerance profile observed in a temporal judgement task was less of a predictor for sensory binding in schizophrenia than for that obtained in controls. We interpret our results as an impairment of temporal event structuring in schizophrenia which does not specifically affect sensory binding operations but rather, the explicit access to timing information associated here with audiovisual speech processing. Our findings are discussed in the context of curent neurophysiological frameworks for the binding and the structuring of sensory events in time.