Brain Topography

, Volume 20, Issue 3, pp 131–141 | Cite as

Measures of Spatial Similarity and Response Magnitude in MEG and Scalp EEG

Original Paper

Abstract

Sensor selection is typically used in magnetoencephalography (MEG) and scalp electroencephalography (EEG) studies, but this practice cannot differentiate between changes in the distribution of neural sources versus changes in the magnitude of neural sources. This problem is further complicated by (1) subject averaging despite sizable individual anatomical differences and (2) experimental designs that produce overlapping waveforms due to short latencies between stimuli. Using data from the entire spatial array of sensors, we present simple multivariate measures that (1) normalize against individual differences by comparison with each individual’s standard response; (2) compare the similarity of spatial patterns in different conditions (angle test) to ascertain whether the distribution of neural sources is different; and (3) compare the response magnitude between conditions which are sufficiently similar (projection test). These claims are supported by applying the reported techniques to a short-term word priming paradigm as measured with MEG, revealing more reliable results as compared to traditional sensor selection methodology. Although precise cortical localization remains intractable, these techniques are easy to calculate, relatively assumption free, and yield the important psychological measures of similarity and response magnitude.

Keywords

EEG MEG Individual/anatomical differences Overlapping waveforms Multivariate analysis Source modeling Repetition priming 

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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  1. 1.Department of Psychology, Neuroscience and Cognitive Science ProgramUniversity of MarylandCollege ParkUSA
  2. 2.Department of PsychologyUniversity of California, San Diego La JollaUSA

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