Neuroimaging researchers have often highlighted sources of method variance associated with specific technical steps in neuroimaging, such as the effects of using different techniques for spatial normalization, movement correction, or modeling the hemo dynamic response. In contrast, because neuroimaging data has usually been collected in relative isolation, much less attention has been paid to overall sources of method variance when attempting to include neuroimaging data as part of a larger multi-method approach. In such a context, attention to the temporal, spatial, and other methodological limitations of PET and fMRI become paramount. Because these limitations substantially influence both the level of noise in the data and the ability to detect relevant activations, they will directly influence the utility of including neuroimaging in a MTMM matrix. The following section describes six important sources of method variance in neuroimaging studies: (a) temporal resolution, (b) the nature and source of the signal change, (c) spatial resolution, (d) anatomical variability, (e) imaging artifacts, and (f) influences on functional activations unrelated to brain processes.
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