Measures of Spatial Similarity and Response Magnitude in MEG and Scalp EEG
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.
KeywordsEEG MEG Individual/anatomical differences Overlapping waveforms Multivariate analysis Source modeling Repetition priming
Unable to display preview. Download preview PDF.
We thank T. Crowley, and V. Hagan for research assistance. This research was supported by NIMH grant MH063993-04.
- 7.Di Lollo V, Enns J, Rensink R. Competition for consciousness among visual events: the psychophysics of reentrant visual processes. J Exp Psychol Gen 2000;131:590–3.Google Scholar
- 11.Halgren E, Baudena P, Clarke JM, Heit G, Marinkovic K, Devaux B, Vignal JP, Biraben A. Intracerebral potentials to rare target and distractor auditory and visual stimuli. II. Medial, lateral and posterior temporal lobe. Electroencephalogr Clin Neurophysiol 1995b;94:229–50.PubMedCrossRefGoogle Scholar
- 15.Huber DE, Tian X, Curran T, O'Reilly RC, Woroch B. The dynamics of integration and separation: ERP, MEG, and neural network studies of immediate repetition effects, submitted.Google Scholar
- 20.Levin DT, Simons DJ. Failure to detect changes to attended objects in motion pictures. Psychon Bull Rev 1997;4:501–6.Google Scholar
- 26.Nunez PL, Srinivasan R. Electric fields of the brain: the neurophysics of EEG. New York: Oxford University Press; 2006.Google Scholar