title: Cluster significance testing using the bootstrap.
abstract: Many of the statistical methods currently employed to analyze fMRI data depend on a response template. However, the true form of the hemodynamic response, and thereby the response template, is often unknown. Consequently, cluster analysis provides a complementary, template-free method for exploratory analysis of multidimensional fMRI data sets. Clustering algorithms currently being applied to fMRI data separate the data into a predefined number of clusters (k). A poor choice of k will result in erroneously partitioning well-defined clusters. Although several clustering algorithms have been successfully applied to fMRI data, techniques for statistically testing cluster separation are still lacking. To address this problem we suggest a method based on Fisher's linear discriminant and the bootstrap. Also introduced in this paper is a measure based on the projection of multidimensional data from two clusters onto the vector, maximizing the ratio of the between- to the within-cluster sums of squares. The resulting one-dimensional distribution may be readily visualized and used as a heuristic for estimating cluster homogeneity. These methods are demonstrated for the self-organizing maps clustering algorithm when applied to event-related fMRI data.
authors.affiliation: Department of Radiology, Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis 55455, USA.
authors.forename: William F
authors.initials: WF
authors.lastname: Auffermann
authors.forename: Shing-Chung
authors.initials: SC
authors.lastname: Ngan
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Hu
mesh_terms: D000465:Algorithms; D001921:Brain / Q000502:physiology; D001931:Brain Mapping / Q000379:methods; D016000:Cluster Analysis; D003463:Cues; D003627:Data Interpretation, Statistical; D005071:Evoked Potentials / Q000502:physiology; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D008959:Models, Neurological; D015203:Reproducibility of Results