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      fMRI correlates of object-based attentional facilitation vs. suppression of irrelevant stimuli, dependent on global grouping and endogenous cueing

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          Abstract

          Theories of object-based attention often make two assumptions: that attentional resources are facilitatory, and that they spread automatically within grouped objects. Consistent with this, ignored visual stimuli can be easier to process, or more distracting, when perceptually grouped with an attended target stimulus. But in past studies, the ignored stimuli often shared potentially relevant features or locations with the target. In this fMRI study, we measured the effects of attention and grouping on Blood Oxygenation Level Dependent (BOLD) responses in the human brain to entirely task-irrelevant events. Two checkerboards were displayed each in opposite hemifields, while participants responded to check-size changes in one pre-cued hemifield, which varied between blocks. Grouping (or segmentation) between hemifields was manipulated between blocks, using common (vs. distinct) motion cues. Task-irrelevant transient events were introduced by randomly changing the color of either checkerboard, attended or ignored, at unpredictable intervals. The above assumptions predict heightened BOLD signals for irrelevant events in attended vs. ignored hemifields for ungrouped contexts, but less such attentional modulation under grouping, due to automatic spreading of facilitation across hemifields. We found the opposite pattern, in primary visual cortex. For ungrouped stimuli, BOLD signals associated with task-irrelevant changes were lower, not higher, in the attended vs. ignored hemifield; furthermore, attentional modulation was not reduced but actually inverted under grouping, with higher signals for events in the attended vs. ignored hemifield. These results challenge two popular assumptions underlying object-based attention. We consider a broader biased-competition framework: task-irrelevant stimuli are suppressed according to how strongly they compete with task-relevant stimuli, with intensified competition when the irrelevant features or locations comprise the same object.

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          Most cited references70

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          Visual search and stimulus similarity.

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            Selective attention and the organization of visual information.

            Theories of visual attention deal with the limit on our ability to see (and later report) several things at once. These theories fall into three broad classes. Object-based theories propose a limit on the number of separate objects that can be perceived simultaneously. Discrimination-based theories propose a limit on the number of separate discriminations that can be made. Space-based theories propose a limit on the spatial area from which information can be taken up. To distinguish these views, the present experiments used small (less than 1 degree), brief, foveal displays, each consisting of two overlapping objects (a box with a line struck through it). It was found that two judgments that concern the same object can be made simultaneously without loss of accuracy, whereas two judgments that concern different objects cannot. Neither the similarity nor the difficulty of required discriminations, nor the spatial distribution of information, could account for the results. The experiments support a view in which parallel, preattentive processes serve to segment the field into separate objects, followed by a process of focal attention that deals with only one object at a time. This view is also able to account for results taken to support both discrimination-based and space-based theories.
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              Shifting visual attention between objects and locations: evidence from normal and parietal lesion subjects.

              Space- and object-based attention components were examined in neurologically normal and parietal-lesion subjects, who detected a luminance change at 1 of 4 ends of 2 outline rectangles. One rectangle end was precued (75% valid); on invalid-cue trials, the target appeared at the other end of the cued rectangle or at 1 end of the uncued rectangle. For normals, the cost for invalid cues was greater for targets in the uncued rectangle, indicating an object-based component. Both right- and left-hemisphere patients showed costs that were greater for contralesional targets. For right-hemisphere patients, the object cost was equivalent for contralesional and ipsilesional targets, indicating a spatial deficit, whereas the object cost for left-hemisphere patients was larger for contralesional targets, indicating an object deficit.
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                Author and article information

                Journal
                Front Integr Neurosci
                Front Integr Neurosci
                Front. Integr. Neurosci.
                Frontiers in Integrative Neuroscience
                Frontiers Media S.A.
                1662-5145
                02 December 2013
                10 February 2014
                2014
                : 8
                : 12
                Affiliations
                [1] 1Cognitive Neuroscience Research Unit, Department of Psychology, City University London London, UK
                [2] 2Neuroimaging Laboratory, Fondazione Santa Lucia, I.R.C.C.S. Rome, Italy
                [3] 3Wellcome Trust Centre for Neuroimaging, University College London London, UK
                [4] 4Institute of Cognitive Neuroscience, University College London London, UK
                Author notes

                Edited by: Vivian Ciaramitaro, University of Massachusetts Boston, USA

                Reviewed by: Zoltán Vidnyánszky, Budapest University of Technology and Economics, Hungary; Taosheng Liu, Michigan State University, USA

                *Correspondence: Elliot D. Freeman, Cognitive Neuroscience Research Unit, Department of Psychology, City University London, Northampton Square, London EC1V 0HB, UK e-mail: elliot.freeman@ 123456city.ac.uk

                This article was submitted to the journal Frontiers in Integrative Neuroscience.

                †Deceased.

                Article
                10.3389/fnint.2014.00012
                3918649
                24574982
                db8564d6-09c5-47d1-a1f6-d3c7616e6cf5
                Copyright © 2014 Freeman, Macaluso, Rees and Driver.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 09 October 2013
                : 20 January 2014
                Page count
                Figures: 7, Tables: 1, Equations: 0, References: 71, Pages: 13, Words: 10501
                Categories
                Neuroscience
                Original Research Article

                Neurosciences
                object-based attention,functional imaging,perceptual grouping,visual cortex,attentional modulation,coherent motion

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