Cue-Invariant Networks for Figure and Background Processing in Human Visual Cortex

Smith-Kettlewell Eye Research Institute, San Francisco, California, United States
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 12/2006; 26(45):11695-708. DOI: 10.1523/JNEUROSCI.2741-06.2006
Source: PubMed


Lateral occipital cortical areas are involved in the perception of objects, but it is not clear how these areas interact with first tier visual areas. Using synthetic images portraying a simple texture-defined figure and an electrophysiological paradigm that allows us to monitor cortical responses to figure and background regions separately, we found distinct neuronal networks responsible for the processing of each region. The figure region of our displays was tagged with one temporal frequency (3.0 Hz) and the background region with another (3.6 Hz). Spectral analysis was used to separate the responses to the two regions during their simultaneous presentation. Distributed source reconstructions were made by using the minimum norm method, and cortical current density was measured in a set of visual areas defined on retinotopic and functional criteria with the use of functional magnetic resonance imaging. The results of the main experiments, combined with a set of control experiments, indicate that the figure region, but not the background, was routed preferentially to lateral cortex. A separate network extending from first tier through more dorsal areas responded preferentially to the background region. The figure-related responses were mostly invariant with respect to the texture types used to define the figure, did not depend on its spatial location or size, and mostly were unaffected by attentional instructions. Because of the emergent nature of a segmented figure in our displays, feedback from higher cortical areas is a likely candidate for the selection mechanism by which the figure region is routed to lateral occipital cortex.

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    • "These results are consistent across participants and also agree with the recent single unit and fMRI literature. As we have noted previously (Appelbaum et al., 2006, Cottereau et al., 2010b), the availability of individually determined functional ROIs makes it possible to pool data across participants in a way that respects individual differences in the location, size and shape of different functional areas. While area V1 and V2 have a consistent relationship to the anatomical landmark of the calcarine sulcus (Hinds et al., 2009), higher-order areas, such as V3A show a large error of variation in their location. "
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    ABSTRACT: Estimating cortical current distributions from electroencephalographic (EEG) or magnetoencephalographic data is a difficult inverse problem whose solution can be improved by the addition of priors on the associated neural responses. In the context of visual activation studies, we propose a new approach that uses a functional area constrained estimator (FACE) to increase the accuracy of the reconstructions. It derives the source correlation matrix from a segmentation of the cortex into areas defined by retinotopic maps of the visual field or by functional localizers obtained independently by fMRI. These areas are computed once for each individual subject and the associated estimators can therefore be reused for any new study on the same participant. The resulting FACE reconstructions emphasize the activity of sources within these areas or enforce their intercorrelations. We used realistic Monte-Carlo simulations to demonstrate that this approach improved our estimates of a diverse set of source configurations. Reconstructions obtained from a real EEG dataset demonstrate that our priors improve the localization of the cortical areas involved in horizontal disparity processing. Hum Brain Mapp, 2012. © 2011 Wiley Periodicals, Inc.
    Full-text · Article · Nov 2012 · Human Brain Mapping
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    • "Considering the temporal aspects of the electrophysiological differences between stack and frame stimuli (>200 msec) in our data, it could be that modulation by attention caused or influenced stack–frame deflections. Recently, however, several studies showed that figure–ground modulation can be found independently from attention (Driver et al. 1992; Kastner et al. 2000; Marcus and Van Essen 2002; Appelbaum et al. 2006; Scholte et al. 2006; but see Ito and Gilbert 1999) and might even guide attentional recourses (Qiu et al. 2007). In this perspective, figure–ground segregation could actually pave the way for prioritizing regions of a visual scene which attention can assign for deeper processing. "
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    ABSTRACT: The ability to distinguish a figure from its background is crucial for visual perception. To date, it remains unresolved where and how in the visual system different stages of figure-ground segregation emerge. Neural correlates of figure border detection have consistently been found in early visual cortex (V1/V2). However, areas V1/V2 have also been frequently associated with later stages of figure-ground segregation (such as border ownership or surface segregation). To causally link activity in early visual cortex to different stages of figure-ground segregation, we briefly disrupted activity in areas V1/V2 at various moments in time using transcranial magnetic stimulation (TMS). Prior to stimulation we presented stimuli that made it possible to differentiate between figure border detection and surface segregation. We concurrently recorded electroencephalographic (EEG) signals to examine how neural correlates of figure-ground segregation were affected by TMS. Results show that disruption of V1/V2 in an early time window (96-119 msec) affected detection of figure stimuli and affected neural correlates of figure border detection, border ownership, and surface segregation. TMS applied in a relatively late time window (236-259 msec) selectively deteriorated performance associated with surface segregation. We conclude that areas V1/V2 are not only essential in an early stage of figure-ground segregation when figure borders are detected, but subsequently causally contribute to more sophisticated stages of figure-ground segregation such as surface segregation.
    Full-text · Article · Nov 2012 · Brain and Behavior
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    • "The shape representation in the LOC is also tuned for small shape changes in the outline of objects (Gillebert et al., 2009; Panis et al., 2008). Our previous source-imaging studies using frequency tagging have suggested that the LOC is tuned for the configuration of a small figure on a larger background (Appelbaum et al., 2010) and that LOC responses to figures are largely cue-invariant (Appelbaum et al., 2006, 2012). Cue-invariance in LOC has also been found with fMRI (Grill-Spector et al., 1998). "
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    ABSTRACT: The lateral occipital cortex (LOC) activates selectively to images of intact objects versus scrambled controls, is selective for the figure-ground relationship of a scene, and exhibits at least some degree of invariance for size and position. Because of these attributes, it is considered to be a crucial part of the object recognition pathway. Here we show that human LOC is critically involved in perceptual decisions about object shape. High-density EEG was recorded while subjects performed a threshold-level shape discrimination task on texture-defined figures segmented by either phase or orientation cues. The appearance or disappearance of a figure region from a uniform background generated robust visual evoked potentials throughout retinotopic cortex as determined by inverse modeling of the scalp voltage distribution. Contrasting responses from trials containing shape changes that were correctly detected (hits) with trials in which no change occurred (correct rejects) revealed stimulus-locked, target-selective activity in the occipital visual areas LOC and V4 preceding the subject's response. Activity that was locked to the subjects' reaction time was present in the LOC. Response-locked activity in the LOC was determined to be related to shape discrimination for several reasons: shape-selective responses were silenced when subjects viewed identical stimuli but their attention was directed away from the shapes to a demanding letter discrimination task; shape-selectivity was present across four different stimulus configurations used to define the figure; LOC responses correlated with participants' reaction times. These results indicate that decision-related activity is present in the LOC when subjects are engaged in threshold-level shape discriminations.
    Full-text · Article · Oct 2012 · NeuroImage
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