Two years ago we posted news of a study by Professor Daryl Bem which seemed to support the idea of 'presentiment', which went on to cause no end of controversy within scientific and skeptical circles (and continues to do so). And now here comes another one on the same topic, although not directly related to Bem: a broad review of experiments so far exploring the presentiment effect, titled "Predictive physiological anticipation preceding seemingly unpredictable stimuli: a meta-analysis. The paper is fairly heavy on terminology and statistics, but here's the basic summary (though 'basic' doesn't do it justice, given the implications of a presentiment effect being proven):
It has been known for some time that arousing and neutral stimuli produce somewhat different post-stimulus physiological responses in humans. However, what is remarkable is that many of the studies examined here make the claim that, for instance, the same physiological measure that yields a differential post-stimulus response to two stimulus classes also yields a differential pre-stimulus response to those same stimulus classes, prior even to the random selection of the stimulus type by the computer. Authors of these studies often refer to the effect as presentiment (sensing an event before it occurs) or unexplained anticipatory activity; we favor the latter terminology as it describes the phenomenon without implying that the effect truly reflects a reversal of the usual forward causality.
Basically, data from experiments appears to show that the body begins reacting to a future event from 2 to 10 seconds *before the event happens*. Needless to say, this is not part of the canon of the current scientific paradigm...
The physiological responses mentioned above are recorded from various sources, including skin conductance, heart rate, blood volume, respiration, electroencephalographic (EEG) activity, pupil dilation, blink rate, and/or blood oxygenation level dependent (BOLD) responses.
The meta-analysis found a small effect size (though many scientific and medical breakthroughs have been smaller), with a high level of significance. The analysis also seemed to rule out the chance that the results were an artifact of poor experimental design, "as higher-quality experiments that addressed known methodological concerns (randomization and expectation bias analysis) produced a quantitatively if not significantly higher overall ES and level of significance than lower-quality studies."
The authors also analysed data from emotional physiology studies that were not investigating the presentiment effect, and found that this data also contained evidence of the phenomenon.
The paper addresses a number of possible 'mundane' explanations for the observed presentiment effect, but found no smoking gun. In the final summary...
...the results of this meta-analysis indicate a clear effect, but we are not at all clear about what explains it. We conclude that if this seemingly anomalous anticipatory activity is real, it should be possible to replicate it in multiple independent laboratories using agreed-upon protocols, dependent variables, and analysis methods. Once this occurs, the problem can be approached with greater confidence and rigor. The cause of this anticipatory activity, which undoubtedly lies within the realm of natural physical processes (as opposed to supernatural or paranormal ones), remains to be determined.
And by that last sentence, I think they mean "well most people would probably describe this as paranormal, but we know we'll lose all the skeptics and scientists if we do that so we'll explicitly disavow it"...
(hat tip to @DavidBMetcalfe)