Sensor selection is typically used in electrophysiological 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 subject averaging despite sizable individual differences in the distribution of the neural sources. Using data from all sensors, we present simple geometric techniques that 1) normalize against individual differences by comparison with a standard response for each individual; 2) compare the similarity of spatial patterns in different conditions (geometric angle) to ascertain whether the distribution of neural sources is different; and 3) compare the response magnitude between conditions which are sufficiently similar (geometric projection). 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. |