fMRI localizer technique: Efficient acquisition and functional properties of single retinotopic positions in the human visual cortex

Kraft, Antje; Schira, Mark M.; Hagendorf, Herbert; Olma, Manuel C.; Brandt, Stephan A.

doi:10.1016/j.neuroimage.2005.05.050

Cited by 24 publications

(21 citation statements)

References 48 publications

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“…Note that linearity of spatial summation does not depend on the weighting function (isotropic 2-D Gaussian) assumed in the model. All linear pRF models that predict the response as a weighted sum of the contrast image necessarily imply linear spatial summation; this is the case even if the weights are anisotropic (Kumano and Uka 2010;Motter 2009;Palmer et al 2012;Schall et al 1986) or if the weights include a negative surround (Cavanaugh et al 2002;Kraft et al 2005;Nurminen et al 2009;Zuiderbaan et al 2012). However, it may be possible to enhance the performance of the CSS model by incorporating a different weighting function into the model.…”

Section: Glm Analysismentioning

confidence: 99%

Compressive spatial summation in human visual cortex

Kay

Winawer

Mezer

et al. 2013

Journal of Neurophysiology

306

450

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Kay KN, Winawer J, Mezer A, Wandell BA. Compressive spatial summation in human visual cortex. J Neurophysiol 110: 481-494, 2013. First published April 24, 2013 doi:10.1152/jn.00105.2013.-Neurons within a small (a few cubic millimeters) region of visual cortex respond to stimuli within a restricted region of the visual field. Previous studies have characterized the population response of such neurons using a model that sums contrast linearly across the visual field. In this study, we tested linear spatial summation of population responses using blood oxygenation level-dependent (BOLD) functional MRI. We measured BOLD responses to a systematic set of contrast patterns and discovered systematic deviation from linearity: the data are more accurately explained by a model in which a compressive static nonlinearity is applied after linear spatial summation. We found that the nonlinearity is present in early visual areas (e.g., V1, V2) and grows more pronounced in relatively anterior extrastriate areas (e.g., LO-2, VO-2). We then analyzed the effect of compressive spatial summation in terms of changes in the position and size of a viewed object. Compressive spatial summation is consistent with tolerance to changes in position and size, an important characteristic of object representation. (Fig. 1). The validity of this assumption is important to examine, as it affects the accuracy of pRF estimates and may reveal insight into response properties at different stages of the visual map hierarchy. Assessments of linearity of spatial summation have been conducted in both electrophysiology and fMRI, but these have provided conflicting conclusions (e.g., Britten and Heuer 1999;Hansen et al. 2004;Kastner et al. 2001;Pihlaja et al. 2008). Thus the precise nature of spatial pooling, and how well the linear approximation describes physiological responses, remains unclear.In this study, we examine spatial summation using systematic measurements of blood oxygenation level-dependent (BOLD) fMRI responses in human visual cortex to a range of spatial contrast patterns. We uncover a small nonlinear effect (subadditive spatial summation) in primary visual cortex and find that the nonlinear effect is pronounced in extrastriate maps. To account for the effect, we develop a computational model in which a compressive static nonlinearity is applied after linear spatial summation; this model substantially improves cross-validation performance compared with a linear spatial summation model.

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Section: Glm Analysismentioning

confidence: 99%

Compressive spatial summation in human visual cortex

Kay

Winawer

Mezer

et al. 2013

Journal of Neurophysiology

306

450

View full text Add to dashboard Cite

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“…Previous studies have successfully utilized a similar passive-viewing localizer approach to assess attentional modulation of face stimuli [14,15], color-checkerboards [29], word-finding processes [64], testing localization of theory-of-mind [45], and testing areas responsive to number symbols and numerosities [51] and objects and houses [39]. …”

Section: Introductionmentioning

confidence: 99%

Top-down attentional control in spatially coincident stimuli enhances activity in both task-relevant and task-irrelevant regions of cortex

Erickson

Prakash

Kim

et al. 2009

Behavioural Brain Research

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Models of selective attention predict that focused attention to spatially contiguous stimuli may result in enhanced activity in areas of cortex specialized for processing task-relevant and task-irrelevant information. We examined this hypothesis by localizing color-sensitive areas (CSA) and word and letter sensitive areas of cortex and then examining modulation of these regions during performance of a modified version of the Stroop task in which target and distractors are spatially coincident. We report that only the incongruent condition with the highest cognitive demand showed increased activity in CSA relative to other conditions, indicating an attentional enhancement in target processing areas. We also found an enhancement of activity in one region sensitive to word/letter processing during the most cognitively demanding incongruent condition indicating greater processing of the distractor dimension. Correlations with performance revealed that top-down modulation during the task was critical for effective filtering of irrelevant information in conflict conditions. These results support predictions made by models of selective attention and suggest an important mechanism of top-down attentional control in spatially contiguous stimuli.

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“…Early visual cortex is retinotopically organized and accordingly it has been demonstrated that BOLD effects resulting from experimental manipulations of visual stimuli are typically neatly restricted to appropriate retinotopic subparts of early visual areas (Mendola et al, 1999; Schira et al, 2004; Kraft et al, 2005). Comparing the responses from different eccentricity ranges (see Figure 4) confirms this principle, demonstrating that in V1–V3 response modulations are restricted to the peripheral subparts while the very foveal subparts of V1–V3 shows very little response to the stimulus presentations.…”

Section: Discussionmentioning

confidence: 99%

Differential Effect of Contrast Polarity Reversals in Closed Squares and Open L-Junctions

Schira¹,

Špehar²

2011

Front. Psychology

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Scene segmentation depends on interaction between geometrical and photometric factors. It has been shown that reversals in contrast polarity at points of highest orientation discontinuity along closed contours significantly impair shape discrimination performance, while changes in contrast polarity at straight(er) contour segments do not have such deleterious effects (Spehar, 2002). Here we employ (semi) high resolution fMRI (1.5 mm × 1.5 mm × 1.5 mm) to investigate the neuronal substrate underlying these perception effects. Stimuli consisted of simple elements (a) squares with contrast reversals along straight segments; (b) squares with contrast reversals in the corner (highest orientation discontinuity); (c) L-Junctions with contrast reversals along the straight ends; (d) L-Junctions with contrast reversals in the corner. Element with contrast polarity reversals are easy to distinguish though appear geometrically equivalent. For squares with contrast polarity reversals only along straight lines we find significantly lower BOLD modulation compared to any of the control conditions, which show similar responses to each other. In the light of previous psychophysical work (Elder and Zucker, 1993; Spehar, 2002) we speculate that this effect is due to closure perception. We observe this across a wide range of areas on occipital cortex.

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fMRI localizer technique: Efficient acquisition and functional properties of single retinotopic positions in the human visual cortex

Cited by 24 publications

References 48 publications

Compressive spatial summation in human visual cortex

Compressive spatial summation in human visual cortex

Top-down attentional control in spatially coincident stimuli enhances activity in both task-relevant and task-irrelevant regions of cortex

Differential Effect of Contrast Polarity Reversals in Closed Squares and Open L-Junctions

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