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Praneeth Namburi

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3 papers

1 author row

YNIMG Journal 2013 Journal Article

Preparatory patterns of neural activity predict visual category search speed

Chun Siong Soon
Praneeth Namburi
Michael W.L. Chee

Rapidly detecting target object categories when objects are embedded in naturalistic scenes is facilitated by preparatory baseline signal changes. However, it is unclear as to what information most strongly predicts perceptual speed in terms of the minimal exposure duration required for accurate detection. Using novel surface-based spatiotemporal pattern classification, we found that while category-specific biases resulting from merely providing a category name can be detected in multiple cortical areas, only biases in lateral occipital complex predicted perceptual speed. These biases likely carry visual semantic information regarding multiple object categories placed in familiar scene contexts. Discriminatory voxels during the preparatory period showed congruent category-selectivity during visual stimulation.

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YNIMG Journal 2011 Journal Article

Cortical surface-based searchlight decoding

Yi Chen
Praneeth Namburi
Lloyd T. Elliott
Jakob Heinzle
Chun Siong Soon
Michael W.L. Chee
John-Dylan Haynes

Local voxel patterns of fMRI signals contain specific information about cognitive processes ranging from basic sensory processing to high level decision making. These patterns can be detected using multivariate pattern classification, and localization of these patterns can be achieved with searchlight methods in which the information content of spherical sub-volumes of the fMRI signal is assessed. The only assumption made by this approach is that the patterns are spatially local. We present a cortical surface-based searchlight approach to pattern localization. Voxels are grouped according to distance along the cortical surface—the intrinsic metric of cortical anatomy—rather than Euclidean distance as in volumetric searchlights. Using a paradigm in which the category of visually presented objects is decoded, we compare the surface-based method to a standard volumetric searchlight technique. Group analyses of accuracy maps produced by both methods show similar distributions of informative regions. The surface-based method achieves a finer spatial specificity with comparable peak values of significance, while the volumetric method appears to be more sensitive to small informative regions and might also capture information not located directly within the gray matter. Furthermore, our findings show that a surface centered in the middle of the gray matter contains more information than to the white–gray boundary or the pial surface.

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YNIMG Journal 2011 Journal Article

Effects of sleep deprivation on cortical activation during directed attention in the absence and presence of visual stimuli

Michael W.L. Chee
Cindy S.F. Goh
Praneeth Namburi
Sarayu Parimal
Katharina N. Seidl
Sabine Kastner

Sleep deprivation (SD) can give rise to faltering attention but the mechanics underlying this remain uncertain. Using a covert attention task that required attention to a peripheral target location, we compared the effects of attention and SD on baseline activity prior to visual stimulation as well as on stimulus-evoked activity. Volunteers were studied after a night of normal sleep (RW) and a night of SD. Baseline signal elevations evoked by preparatory attention in the absence of visual stimulation were attenuated within rFEF, rIPS (sparing SEF) and all retinotopically mapped visual areas during SD, indicative of impaired endogenous attention. In response to visual stimuli, attention modulated activation in higher cortical areas and extrastriate cortex (hV4, ventral occipital areas) after RW. SD attenuated rFEF, rIPS, V3a and VO stimulus-evoked activation regardless of whether stimuli were attended. Notably, the modulation of stimulus-evoked activation by attention was not affected by SD unlike for the preparatory period, suggesting a reduced number, but still functional circuits during SD. Deficits in endogenous attention in SD dominate in the preparatory period, whereas changes in stimulus-related activation arise from an interaction between compromised fronto-parietal top-down control of attention and reduced sensitivity of extrastriate visual cortex to top-down or bottom-up inputs.

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