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Setu Havanur, Glyn Humphreys, Harriet Allen; The effect of background grouping on central task in patients with parietal lobe lesions. Journal of Vision 2010;10(7):1197. doi: 10.1167/10.7.1197.
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We investigated the effects of grouping between irrelevant background stimuli on a central task. We compared performance between non-lesioned control participants and patients with visual neglect and extinction. Our patient group included right and left visual neglect patients. On each trial participants reported the presence or absence of a central target (a single digit) presented on (0.5 contrast) random noise patch (duration =100ms). The visibility of the central target was matched between participants such that performance on a pretest was always 80% correct. In addition to the central stimulus a pattern of black and white dots was presented on either side of fixation on a gray background. Those dots were either arranged in alternating rows of black and white dots or randomly placed in the same matrix (intermixed in a single block). Patients were faster (p=0.03) on the central task when the background dots were in rows compared to when they were in random positions. However, the main effects of the field, patient group (left vs right hemisphere lesion) and their interactions were not significant. We did not find this effect of grouping in the non-lesioned control participants (Fs<1). These effects were not due to explicit recognition of the background pattern since no patient was able to report the presence of the grouping; only 3 patients mentioned the dots and out of them only two patients reported them being black and white. We found facilitation of a central detection task by grouping within the background pattern, even though this background pattern could not be explicitly reported. This implies that simple forms of grouping can occur without attention.
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