The effects of single-trial averaging upon the spatial extent of fMRI activation.

by: SA Huettel, G McCarthy

Neuroreport, Vol. 12, No. 11. (8 August 2001), pp. 2411-2416.

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Abstract

We examined effects of trial averaging upon spatial extent, spatial topography, and temporal properties of fMRI activation. Two subjects participated in an event-related visual stimulation design. There was an exponential relation between number of trials and spatial extent, such that additional trials identified, on average, a constant proportion of the remaining voxels. At values typical of fMRI experimentation (e.g. 50 trials) only about 50% of eventually active voxels were significant; asymptotic values were approached by 150 trials. The variability of the estimated hemodynamic response decreased with signal averaging, becoming stable across samples of > or = 25 trials. Therefore, group or condition differences may result from differences in voxelwise noise exacerbated by averaging small numbers of trials.

@article{citeulike:1115346, abstract = {We examined effects of trial averaging upon spatial extent, spatial topography, and temporal properties of fMRI activation. Two subjects participated in an event-related visual stimulation design. There was an exponential relation between number of trials and spatial extent, such that additional trials identified, on average, a constant proportion of the remaining voxels. At values typical of fMRI experimentation (e.g. 50 trials) only about 50\% of eventually active voxels were significant; asymptotic values were approached by 150 trials. The variability of the estimated hemodynamic response decreased with signal averaging, becoming stable across samples of > or = 25 trials. Therefore, group or condition differences may result from differences in voxelwise noise exacerbated by averaging small numbers of trials.}, address = {Brain Imaging and Analysis Center, Duke University Medical Center, Box 3918, Durham, NC 27710, USA.}, author = {Huettel, S. A. and McCarthy, G. }, citeulike-article-id = {1115346}, issn = {0959-4965}, journal = {Neuroreport}, keywords = {fmri, single-trial\_averaging}, month = {August}, number = {11}, pages = {2411--2416}, posted-at = {2007-02-20 23:03:50}, priority = {2}, title = {The effects of single-trial averaging upon the spatial extent of fMRI activation.}, url = {http://view.ncbi.nlm.nih.gov/pubmed/11496120}, volume = {12}, year = {2001} }

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TY - JOUR ID - citeulike:1115346 L3 - citeulike-article-id:1115346 TI - The effects of single-trial averaging upon the spatial extent of fMRI activation. JF - Neuroreport VL - 12 IS - 11 SP - 2411 EP - 2416 AD - Brain Imaging and Analysis Center, Duke University Medical Center, Box 3918, Durham, NC 27710, USA. SN - 0959-4965 N2 - We examined effects of trial averaging upon spatial extent, spatial topography, and temporal properties of fMRI activation. Two subjects participated in an event-related visual stimulation design. There was an exponential relation between number of trials and spatial extent, such that additional trials identified, on average, a constant proportion of the remaining voxels. At values typical of fMRI experimentation (e.g. 50 trials) only about 50% of eventually active voxels were significant; asymptotic values were approached by 150 trials. The variability of the estimated hemodynamic response decreased with signal averaging, becoming stable across samples of > or = 25 trials. Therefore, group or condition differences may result from differences in voxelwise noise exacerbated by averaging small numbers of trials. KW - fmri KW - single-trial_averaging AU - Huettel, SA AU - McCarthy, G PY - 2001/08/08/ UR - http://view.ncbi.nlm.nih.gov/pubmed/11496120 ER -

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