Reproducibility of functional network metrics and network structure: A comparison of task-related BOLD, resting ASL with BOLD contrast, and resting cerebral blood flow

Network analysis is an emerging approach to functional connectivity in which the brain is construed as a graph and its connectivity and information processing estimated by mathematical characterizations of graphs. There has been little to no work examining the reproducibility of network metrics derived from different types of functional magnetic resonance imaging (fMRI) data (e.g., resting vs. task related, or pulse sequences other than standard blood oxygen level dependent [BOLD] data) or of measures of network structure at levels other than summary statistics. Here, we take up these questions, comparing the reproducibility of graphs derived from resting arterial spin-labeling perfusion fMRI with those derived from BOLD scans collected while the participant was performing a task. We also examine the reproducibility of the anatomical connectivity implied by the graph by investigating test–retest consistency of the graphs’ edges. We compare two measures of graph-edge consistency both within versus between subjects and across data types. We find a dissociation in the reproducibility of network metrics, with metrics from resting data most reproducible at lower frequencies and metrics from task-related data most reproducible at higher frequencies; that same dissociation is not recapitulated, however, in network structure, for which the task-related data are most consistent at all frequencies. Implications for the practice of network analysis are discussed.     

Resolving conflict: A response to Martin and Cheng (2006)

Martin and Cheng (2006) report the results of an experiment aimed at disentangling the effects of association strength from those of competition on performance on a verb generation task. Their experiment is situated at the center of a putative debate regarding the function of the left inferior frontal gyrus in language processing (see, e.g., Wagner, Paré-Blagoev, Clark, & Poldrack, 2001). Following in this tradition, Martin and Cheng purport to contrast two processes—selection between competing representations and controlled retrieval of weak associates—that we argue can be reduced to the same mechanism. We contend that the distinction between competition and association strength is a false dichotomy, and we attempt to recast this discussion within a Bayesian framework in an attempt to guide research in this area in a more fruitful direction.     

A typology of motor vehicle consumers using motives for leasing versus financing

• Previous consumer research suggests that individuals who finance high‐cost items tend to differ from those who lease the same items. Some differences are economic, such as income and wealth, while other dissimilarities involve non‐economic issues such as personal preferences. We employ non‐hierarchical cluster analysis to create consumer segments of motor vehicle lessees and financers based on motives for leasing versus financing and demographics. Five segments were uncovered. Lessees predominate in two categories: budget gourmets and automotive hedonists. Another two categories, utility seekers and basic transportation seekers, are mainly comprised of financers. The final group, mature luxury seekers, consists of a roughly equal mix of lessees and financers. Differences between the segments are addressed here, along with a discussion of findings and implications.

Copyright © 2006 John Wiley & Sons, Ltd.