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Laurence Lalanne, Anne Giersch; Temporal and spatial grouping: questions derived from studies in patients with schizophrenia. Journal of Vision 2010;10(7):1395. doi: 10.1167/10.7.1395.
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© ARVO (1962-2015); The Authors (2016-present)
Patients with schizophrenia are known to have an impaired sense of continuity, which, according to Husserl, involves the integration of past, present and future moments. The experience of present time is thus not a point but a period in time. It can be evaluated by means of simple psychophysics experiments, in which two bars appear simultaneously or asynchronously, and then stay on the screen until subjects decide whether the bars appeared synchronously or not. Healthy volunteers typically judge bars as synchronous for SOAs up to 30 to 50 ms, in contrast with patients, who require a longer SOA to detect that bars are asynchronous. However in these studies, bars were systematically presented in different hemi-fields, and a qualitative and quantitative impairment of inter-hemispheric transfer has been suggested to exist in patients with schizophrenia. This impairment could explain why time windows are larger in patients when bars appear in two different hemi-fields. We checked this hypothesis by manipulating the location of the squares, displayed in either the same or across hemi-fields. Continuous eye tracking ensured that subjects looked at a central fixation point. SOAs varied between 0 and 96 ms, and subjects decided if squares appeared synchronously or not. Results showed an enlarged time window in patients but no location effect (intra versus inter-hemispheric presentation). Furthermore the analysis of the Simon effect showed that patients are sensitive to very short duration stimuli (8.3 ms). This suggests that the enlargement of the time window is not associated with a fusion of events in time, but rather to a difficult comparison between stimuli onsets. As the two stimuli are clearly separated in space, this leads to the question of the relationship between spatial and temporal event-coding. We will especially discuss the possibility that comparing time-onsets requires mental grouping of the compared stimuli.
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