Increasing the accuracy of electromagnetic inverses using functional area source correlation constraints

Cottereau, Benoit R.; Ales, Justin; Norcia, Anthony M.

doi:10.1002/hbm.21394

Cited by 26 publications

(51 citation statements)

References 77 publications

(93 reference statements)

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“…Our data do not contradict this result, but do suggest that, at least for rotation symmetry, other areas may contribute to the symmetry processing in LOC. A potential avenue for resolving this question is the combination of source-localized EEG and response-locked analysis techniques, which have successfully been applied to investigating the causal role of different visual areas in other perceptual domains (Ales et al, 2013;Cottereau et al, 2014).…”

Section: Discussionmentioning

confidence: 99%

“…Cortical current density estimates of the neural responses were obtained from an L2 minimum-norm inverse of the forward model as described in a recent study by Cottereau et al (2012). We used the functionally defined visual ROIs to constrain these estimates by modifying the source-covariance matrix.…”

Section: Methodsmentioning

confidence: 99%

“…These within-participant ROI averages were then averaged across participants to generate crossparticipant averages for each ROI. This procedure has been shown to reduce cross talk between different cortical ROIs, resulting in better area resolution in the group inversion than can be achieved in single participants (Cottereau et al, 2015).…”

Section: Methodsmentioning

confidence: 99%

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Representation of Maximally Regular Textures in Human Visual Cortex

et al. 2016

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Here we expand on this work by investigating a class of textures that have maximal formal regularity, the 17 crystallographic wallpaper groups (Fedorov, 1891). We used texture stimuli from four of the groups that differ in the maximum order of rotation symmetry they contain, and measured neural responses in human participants using functional MRI and high-density EEG. We found that cortical area V3 has a parametric representation of the rotation symmetries in the textures that is not present in either V1 or V2, the first discovery of a stimulus property that differentiates processing in V3 from that of lower-level areas. Parametric responses were also seen in higherorder ventral stream areas V4, VO1, and lateral occipital complex (LOC), but not in dorsal stream areas. The parametric response pattern was replicated in the EEG data, and source localization indicated that responses in V3 and V4 lead responses in LOC, which is consistent with a feedforward mechanism. Finally, we presented our stimuli to four well developed feedforward models and found that none of them were able to account for our results. Our results highlight structural regularity as an important stimulus dimension for distinguishing the early stages of visual processing, and suggest a previously unrecognized role for V3 in the visual form-processing hierarchy.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Representation of Maximally Regular Textures in Human Visual Cortex

et al. 2016

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“…Detailed discussion of the source imaging procedure is provided in Cottereau et al (2012), and we provide some essential details below. The sources were constrained to the location and orientation of the cortical surface (Cottereau et al, 2012;Dale et al, 2000;Hamalainen and Ilmoniemi, 1994). We used a mid-gray cortical surface that was down sampled to have 20,484 isotropically spaced vertices.…”

Section: Source Imaging Proceduresmentioning

confidence: 99%

The time course of shape discrimination in the human brain

et al. 2013

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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.

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“…In addition, we modified the source covariance matrix in two ways to decrease the tendency of the minimum norm procedure to place sources outside of the visual areas. These constraints involved the following: (1) increasing the variance allowed within the visual areas by a factor of two relative to other vertices and (2) enforcement of a local smoothness constraint within an area using the first-and second-order neighborhoods on the mesh with a weighting function equal to 0.5 for the first order and 0.25 for the second (Cottereau et al, 2011a). The smoothness constraint therefore respects areal boundaries unlike other smoothing methods such as lowresolution brain electromagnetic tomography that apply the same smoothing rule throughout cortex (Pascual-Marqui et al, 1994).…”

Section: Cortically Constrained Inversementioning

confidence: 99%

The Selectivity of Task-Dependent Attention Varies with Surrounding Context

Kim

Verghese

2012

J. Neurosci.

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Attention is thought to operate by enhancing the target of interest and suppressing the surroundings. We hypothesized that the spatial profile of attention depends on the surround's relationship to the target. Using high-density electroencephalographic measurements, we examined the spatial profile of attention to a grating target surrounded by an annular grating that was either coextensive with the target (unsegmented) or appeared segmented from it due to a gap or phase offset. We directly probed the spread of attention from the central target into the surround by flickering the surround and monitoring frequency-tagged steady-state visual-evoked potentials. Observers were required to detect a contrast increment that occurred only on the target. Successful detection of the increment required selecting the target and suppressing the surround, particularly when the target did not readily segment from the surround. The profile of attention was investigated in five visual regions of interest (ROIs) (V1, V4, V3A, lateral occipital complex, and human middle temporal area), mapped in a separate anatomical magnetic resonance imaging scan. We found that in most ROIs, attention to the target generated smaller responses from the surrounding annulus when it was contiguous compared with when it was clearly segmented. This result shows that the profile of attention depends on task demands and on surrounding context; attention is tightly focused when the target region needs to be isolated but loosely focused when the target region is clearly segmented.

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Increasing the accuracy of electromagnetic inverses using functional area source correlation constraints

Cited by 26 publications

References 77 publications

Representation of Maximally Regular Textures in Human Visual Cortex

Representation of Maximally Regular Textures in Human Visual Cortex

The time course of shape discrimination in the human brain

The Selectivity of Task-Dependent Attention Varies with Surrounding Context

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