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O.J. Braddick, J. Aspell, J. Atkinson, J. Wattam–Bell; Temporal Integration Of Global Pattern Information . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4662.
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Purpose: The ability to detect global organization in an array of oriented line segments has been taken as a measure of the performance of extrastriate cortical mechanisms that can integrate pattern information over an extended region of the visual field. Spatial pattern organization is possible with various degrees of complexity, e.g. parallel texture vs concentric circles. Do these different types of organization involve different levels of processing in the visual system? We have previously considered spatial integration for these tasks (Braddick et al ECVP 2000); here we address this question by asking whether they differ in the temporal interval over which they show integration of information. Longer integration time might be expected to be a feature of higher–level processing in the visual system. Methods: Stimuli were arrays of line segments containing a central circular region, within which a variable percentage of segments were coherent, i.e. aligned either parallel to a common orientation (vertical or horizontal) or to concentric circles. Subjects were required to discriminate between 0% and other coherence values, in either a spatial 2AFC or a 2IFC design, with randomly oriented arrays presented before and after each display acting as masks to limit processing time. Target coherence was varied according to an adaptive rule to determine threshold. In different runs, the duration of stimulus intervals was varied between 27 and 1067 ms. Log coherence thresholds for parallel and concentric patterns were plotted as a function of stimulus duration, and fitted with a double–linear function to estimate critical duration. Results: Critical duration for detecting the coherence of concentric patterns (mean = 196 ms) was consistently shorter than for parallel patterns (mean = 299 ms) . Conclusions: Despite requiring more complex spatial operations, information for detecting concentric organization is integrated over a shorter temporal period than that for parallel organization. Concentric patterns can be processed by a rapid pathway, presumably forming an intermediate stage in the global processing of specific forms including faces. The longer integration time for parallel patterns throws doubt on a simply hierarchical model of pattern processing. Results will be discussed in the light of imaging evidence on the brain areas differentially activated by coherent and incoherent global patterns.
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