The choice of a proper reference is very important issue in EEG studies. Any electrode on the head has its own fluctuation of potential which inflates the apparent synchrony and any activity at the reference electrode that is intermittently high and low can imitate the patterns of synchrony. In this work two reference positions are used in order to study the reference influence for the patterns detection process. The detection and classification process is based on a multi-step procedure that includes the location of the patterns in time, spectrum and space. EEG amplitude modulation patterns were found from all subjects that could be classified with respect to stimulus combination type significantly above chance levels. The patterns were found in the beta range (15–22 Hz band) and they occurred in three short bursts following the stimulus onset. The result showed that the patterns were non-local, occupying the entire array and no channel lies outside the fields to be classified, but that the location of the reference has no significant effect on the multivariate classification because similar classification rates can be obtained for different references.