RESUMO
A popular model for the representation of time in the brain posits the existence of a single, central-clock. In that framework, temporal distortions in perception are explained by contracting or expanding time over a given interval. We here present evidence for an alternative account, one which proposes multiple independent timelines coexisting within the brain and stresses the importance of motor predictions and causal inferences in constructing our temporal representation of the world. Participants judged the simultaneity of a beep and flash coming from a single source at different distances. The beep was always presented at a constant delay after a motor action, while the flash occurred at a variable delay. Independent shifts in the implied timing of the auditory stimulus toward the motor action (but not the visual stimulus) provided evidence against a central-clock model. Additionally, the hypothesis that the time between action and delayed effect is compressed (known as intentional binding) seems unable to explain our results: firstly, because actions and effects can perceptually reverse, and secondly because the recalibration of simultaneity remains even after the participant's intentional actions are no longer present. Contrary to previous reports, we also find that participants are unable to use distance cues to compensate for the relatively slower speed of sound when audio-visual events are presented in depth. When a motor act is used to control the distal event, however, adaptation to the delayed auditory signal occurs and subjective cross-sensory synchrony is maintained. These results support the hypothesis that perceptual timing derives from and is calibrated by our motor interactions with the world.
RESUMO
Research in schizophrenia has tended to emphasize deficits in higher cognitive abilities, such as attention, memory, and executive function. Here we provide evidence for dysfunction at a more fundamental level of perceptual processing, temporal integration. On a measure of flicker fusion, patients with schizophrenia exhibited significantly lower thresholds than age and education matched healthy controls. We reasoned that this finding could result from a longer window of temporal integration or could reflect diminished repetition suppression: if every frame of the repeating stimulus were represented as novel, its perceived duration would be accordingly longer. To tease apart these non-exclusive hypotheses, we asked patients to report the number of stimuli perceived on the screen at once (numerosity) as they watched rapidly flashing stimuli that were either repeated or novel. Patients reported significantly higher numerosity than controls in all conditions, again indicating a longer window of temporal integration in schizophrenia. Further, patients showed the largest difference from controls in the repeated condition, suggesting a possible effect of weaker repetition suppression. Finally, we establish that our findings generalize to several different classes of stimuli (letters, pictures, faces, words, and pseudo-words), demonstrating a non-specific effect of a lengthened window of integration. We conclude that the visual system in schizophrenics integrates input over longer periods of time, and that repetition suppression may also be deficient. We suggest that these abnormalities in the processing of temporal information may underlie higher-level deficits in schizophrenia and account for the disturbed sense of continuity and fragmentation of events in time reported by patients.
