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

Journal Article (Journal Article)

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.

Full Text

Duke Authors

Cited Authors

  • Huettel, SA; McCarthy, G

Published Date

  • August 2001

Published In

Volume / Issue

  • 12 / 11

Start / End Page

  • 2411 - 2416

PubMed ID

  • 11496120

Electronic International Standard Serial Number (EISSN)

  • 1473-558X

International Standard Serial Number (ISSN)

  • 0959-4965

Digital Object Identifier (DOI)

  • 10.1097/00001756-200108080-00025


  • eng