cluster extent
The spatial size of a contiguous group of activated voxels, typically measured in number of voxels or volume.
Full Definition
Cluster extent refers to the spatial size of contiguous regions of statistically significant activation in neuroimaging analyses, typically measured as the number of voxels or total volume of tissue showing effects above a specified threshold. In neuroinformatics, cluster extent is a key component of multiple comparisons correction strategies, where both the intensity of activation (height threshold) and spatial extent (cluster size) are considered for statistical significance. Large cluster extents may indicate more reliable or widespread effects, though interpretation depends on the specific analysis context. Cluster extent thresholding is commonly used in conjunction with voxel-wise thresholds to control family-wise error rates while maintaining sensitivity to spatially distributed activation patterns. The minimum cluster extent for significance is typically determined through Monte Carlo simulations or analytical methods.
Usage
Usage note: Specify units (voxels or mm³) and thresholding criteria clearly in methods.
In Context
- "Significant clusters were required to exceed 50 voxels in extent at p < 0.05 corrected." — Statistical thresholding criteria
- "The activation cluster showed an extent of 1,247 voxels spanning multiple cytoarchitectonic areas." — Activation mapping results