May: Correlation between Psychophysiological Variables A Methodological Issue in the Study of Correlation between Psychophysiological Variables

We used previously accumulated skin conductance (SC) and EEG data to examine the effects of their respective autocorrelations upon hypothesis testing. We found that SC data remain autocorrelated for many seconds, and that EEG data remain autocorrelated for many fractions of a second depending upon filtering parameters. We show that the effect of these non-zero autocorrelations upon the interpretation of correlation coefficients using normal statistics can lead to substantial and artifactually inflated significance levels. With SC, for example, the high autocorrelation can lead to a Pearson’s r correlation of 1.0 even under the null hypothesis. The resulting nullhypothesis z-score distribution range is [-20,20]; whereas, is should be approximately in the range [-3,3]. Alpha EEG, while less autocorrelated than SC, still leads to Pearson’s r correlations in the range [-0.4,0.4] leading to a null-hypothesis z-score distribution in the range [-15,15]. Beta band EEG reduces the null-hypothesis z-score range to [-5,5]. We demonstrate that standard Monte Carlo techniques can provide valid estimates of the significance levels. The underlying assumptions of conventional statistical tests can be easily ignored, and the resulting error may become embedded into the thinking of a research community. As an example, we critically review a paper claiming significant correlation between the EEG’s of isolated subjects (Grinberg-Zylberbaum, Delaflor, Attie, and Goswami, 1994); however, using uncorrelated EEG data from one of our previous studies and Monte Carlo methods to model the true null hypothesis, we compute a non-significant difference (Z = 1.22) between their non-“correlated” subjects and their “correlated” ones. As a result of their, possibly incorrect, interpretation of these correlations there is a growing literature proclaiming that these experiments are evidence for EPR-like quantum connections in isolated brains. These putative connections have been used as explanations, or at least plausibility arguments, for a variety of phenomena including distant healing.