Experimental Evidence for Anomalous Retroactive Influences on Cognition

Journal of Personality and Social PsychologyFeeling the Future: Experimental Evidence for AnomalousRetroactive Influences on Cognition and AffectDaryl J. BemOnline First Publication, January 31, 2011. doi: 10.1037/a0021524CITATIONBem, D. J. (2011, January 31). Feeling the Future: Experimental Evidence for AnomalousRetroactive Influences on Cognition and Affect. Journal of Personality and Social Psychology.Advance online publication. doi: 10.1037/a0021524Journal of Personality and Social Psychology2011, Vol. ●●, No. ●, 000 – 000© 2011 American Psychological Association0022-3514/11/$12.00 DOI: 10.1037/a0021524Feeling the Future: Experimental Evidence for Anomalous RetroactiveInfluences on Cognition and AffectDaryl J. BemCornell UniversityThe term psi denotes anomalous processes of information or energy transfer that are currently unexplained in terms of known physical or biological mechanisms. Two variants of psi are precognition(conscious cognitive awareness) and premonition (affective apprehension) of a future event that could nototherwise be anticipated through any known inferential process. Precognition and premonition arethemselves special cases of a more general phenomenon: the anomalous retroactive influence of somefuture event on an individual’s current responses, whether those responses are conscious or nonconscious, cognitive or affective. This article reports 9 experiments, involving more than 1,000 participants,that test for retroactive influence by “time-reversing” well-established psychological effects so that theindividual’s responses are obtained before the putatively causal stimulus events occur. Data are presentedfor 4 time-reversed effects: precognitive approach to erotic stimuli and precognitive avoidance ofnegative stimuli; retroactive priming; retroactive habituation; and retroactive facilitation of recall. Themean effect size (d) in psi performance across all 9 experiments was 0.22, and all but one of theexperiments yielded statistically significant results. The individual-difference variable of stimulus seeking, a component of extraversion, was significantly correlated with psi performance in 5 of theexperiments, with participants who scored above the midpoint on a scale of stimulus seeking achievinga mean effect size of 0.43. Skepticism about psi, issues of replication, and theories of psi are alsodiscussed.Keywords: psi, parapsychology, ESP, precognition, retrocausationPrecognition and premonition are themselves special cases of amore general phenomenon: the anomalous retroactive influence ofsome future event on an individual’s current responses, whetherthose responses are conscious or nonconscious, cognitive or affective. This article reports nine experiments designed to test for suchretroactive influence by “time-reversing” several well-establishedpsychological effects, so that the individual’s responses are obtained before the putatively causal stimulus events occur.Psi is a controversial subject, and most academic psychologistsdo not believe that psi phenomena are likely to exist. A survey of1,100 college professors in the United States found that psychologists were much more skeptical about the existence of psi thanwere their colleagues in the natural sciences, the other socialsciences, or the humanities (Wagner & Monnet, 1979). In fact,34% of the psychologists in the sample declared psi to be impossible, a view expressed by only 2% of all other respondents.Although our colleagues in other disciplines would probably agreewith the oft-quoted dictum that “extraordinary claims requireextraordinary evidence,” we psychologists are more likely to befamiliar with the methodological and statistical requirements forsustaining such claims and aware of previous claims that failedeither to meet those requirements or to survive the test of successful replication. Several other reasons for our greater skepticism arediscussed by Bem and Honorton (1994, pp. 4 –5).There are two major challenges for psi researchers, one empirical and one theoretical. The major empirical challenge, of course,is to provide well-controlled demonstrations of psi that can bereplicated by independent investigators. That is the major goal inthe research program reported in this article. Accordingly, theThe term psi denotes anomalous processes of information orenergy transfer that are currently unexplained in terms of knownphysical or biological mechanisms. The term is purely descriptive;it neither implies that such phenomena are paranormal nor connotes anything about their underlying mechanisms. Alleged psiphenomena include telepathy, the apparent transfer of informationfrom one person to another without the mediation of any knownchannel of sensory communication; clairvoyance (sometimescalled remote viewing), the apparent perception of objects orevents that do not provide a stimulus to the known senses; psychokinesis, the apparent influence of thoughts or intentions onphysical or biological processes; and precognition (conscious cognitive awareness) or premonition (affective apprehension) of afuture event that could not otherwise be anticipated through anyknown inferential process.I am grateful to the students who served as head research assistants andlaboratory coordinators for their enthusiasm and dedication to this controversial enterprise: Ben Edelman, Rebecca Epstein, Dan Fishman, JamisonHahn, Eric Hoffman, Kelly Lin, Brianne Mintern, Brittany Terner, andJade Wu. I am also indebted to the 30 other students who served as friendlyand reliable experimenters over the course of this research program. DeanRadin, senior scientist at the Institute of Noetic Sciences (IONS), andDavid Sherman, professor of psychology at the University of California,Santa Barbara, provided valuable guidance in the preparation of this article.Correspondence concerning this article should be addressed to Daryl J.Bem, Department of Psychology, Uris Hall, Cornell University, Ithaca, NY14853. E-mail: d.bem@cornell.edu12experiments have been designed to be as simple and transparent aspossible, drawing participants from the general population, requiring no instrumentation beyond a desktop computer, taking lessthan thirty minutes per session, and requiring statistical analysesno more complex than a t test across sessions or participants.The major theoretical challenge for psi researchers is to providean explanatory theory for the alleged phenomena that is compatible with physical and biological principles. Although the currentabsence of an explanatory theory for psi is a legitimate rationalefor imposing the “extraordinary” requirement on the evidence, it isnot, I would argue, sufficient reason for rejecting all profferedevidence a priori. Historically, the discovery and scientific exploration of most phenomena have preceded explanatory theories,often by decades or even centuries. The major focus of this articleis empirical, but I return to a brief discussion of theory at the end.As noted above, the experiments in this article are concernedwith apparent retroactive influence, a generalized form of precognition. Experimental tests of precognition have been reported formore than half a century. Most of the early experiments usedforced-choice designs in which participants were explicitly challenged to guess which one of several potential targets would berandomly selected at a later time. Typical targets have been ESPcard symbols, an array of colored lightbulbs, the faces of a die, orvisual elements in a computer display. When a participant correctly selects the actual target-to-be, it is designated as a hit, andpsi performance is typically expressed as the hit rate, the percentage of hits over trials.A meta-analysis of all forced-choice precognition experimentsappearing in English-language journals between 1935 and 1977was published by Honorton and Ferrari (1989). Their analysisincluded 309 experiments conducted by 62 different investigatorsand involving more than 50,000 participants. Honorton and Ferrarireported a small but consistent and highly significant hit rate(mean z 0.69, combined z 12.14, p 6 10 27). They alsoconcluded that this overall result was unlikely to be significantlyinflated by the selective reporting of positive results (the so-calledfile-drawer effect): There would have to be 46 unreported studiesaveraging null results for every reported study in the meta-analysisto reduce the overall significance of the database to nonsignificance.Just as research in cognitive social psychology has increasinglypursued the study of cognitive and affective processes that are notaccessible to conscious awareness and control (Bargh & Ferguson,2000), research in psi has followed the same path, moving fromexplicit forced-choice guessing tasks to experiments using subliminal stimuli and implicit, indirect, or physiological responses. Thetrend is exemplified by several recent “presentiment” experiments,pioneered by Radin (1997), in which physiological indices ofparticipants’ emotional arousal were monitored as participantsviewed a series of pictures on a computer screen. Most of thepictures were emotionally neutral, but a highly arousing negativeor erotic image was displayed on randomly selected trials. Asexpected, strong emotional arousal occurred when these imagesappeared on the screen, but the remarkable finding is that theincreased arousal was observed to occur a few seconds before thepicture appeared, before the computer had even selected the picture to be displayed. The presentiment effect has also been demonstrated in an fMRI experiment that monitored brain activity(Bierman & Scholte, 2002) and in experiments using bursts ofBEMnoise rather than visual images as the arousing stimuli (Spottiswoode & May, 2003). A review of presentiment experiments priorto 2006 can be found in Radin (2006, pp. 161–180). Althoughthere has not yet been a formal meta-analysis of presentimentstudies, there have been 24 studies with human participantsthrough 2009, of which 19 were in the predicted direction andabout half were statistically significant. Two studies with animalswere both positive, one marginally and the other substantially so(D. I. Radin, personal communication, December 20, 2009).Most of the experiments reported in this article are also part ofthis trend toward using subliminal stimulus presentations andindirect or implicit response measures. Each of them modified awell-established psychological effect by reversing the usual sequence of events, so that the individual’s responses were obtainedbefore rather than after the stimulus events occurred. Table 1provides an overview of the effects and their corresponding timereversed experiments.Precognitive Approach and AvoidanceThe presentiment studies provide evidence that our physiologycan anticipate unpredictable erotic or negative stimuli before theyoccur. Such anticipation would be evolutionarily advantageous forreproduction and survival if the organism could act instrumentallyto approach erotic stimuli and avoid negative stimuli. The twoexperiments in this section were designed to test whether individuals can do so.Experiment 1: Precognitive Detection of Erotic StimuliAs noted above, most of the earlier experiments in precognitionexplicitly challenged participants to guess which one of severalstimuli would be randomly selected after they recorded their guess.In most of these experiments, participants were also given explicittrial-by-trial feedback on their performance. This first experimentadopts this traditional protocol, using erotic pictures as explicitreinforcement for correct “precognitive” guesses.MethodOne hundred Cornell undergraduates, 50 women and 50 men,were recruited for this experiment through the Psychology Depart-Table 1Overview of Psychological Effects and Their CorrespondingTime-Reversed ExperimentsStandard psychological effectExperimentsApproach/avoidance1. Precognitive Detection of EroticStimuli2. Precognitive Avoidance of NegativeStimuli3. Retroactive Priming I4. Retroactive Priming II5. Retroactive Habituation I6. Retroactive Habituation II7. Retroactive Induction of Boredom8. Retroactive Facilitation of Recall I9. Retroactive Facilitation of Recall IIAffective primingHabituationFacilitation of recallFEELING THE FUTUREment’s automated online sign-up system.1 They either receivedone point of experimental credit in a psychology course offeringthat option or were paid $5 for their participation. Both therecruiting announcement and the introductory explanation given toparticipants upon entering the laboratory informed them thatthis is an experiment that tests for ESP. It takes about 20 minutes andis run completely by computer. First you will answer a couple of briefquestions. Then, on each trial of the experiment, pictures of twocurtains will appear on the screen side by side. One of them has apicture behind it; the other has a blank wall behind it. Your task is toclick on the curtain that you feel has the picture behind it. The curtainwill then open, permitting you to see if you selected the correctcurtain. There will be 36 trials in all.Several of the pictures contain explicit erotic images (e.g., couplesengaged in nonviolent but explicit consensual sexual acts). If youobject to seeing such images, you should not participate in thisexperiment.The participant then signed a consent form and was seated infront of the computer. After responding to two individualdifference items (discussed below), the participant had a 3-minrelaxation period during which the screen displayed a slowlymoving Hubble photograph of the starry sky while peaceful newage music played through stereo speakers. The 36 trials beganimmediately after the relaxation period.Stimuli. Most of the pictures used in this experiment wereselected from the International Affective Picture System (IAPS;Lang & Greenwald, 1993), a set of 820 digitized photographs thathave been rated on 9-point scales for valence and arousal by bothmale and female raters. This is the same source of pictures used inmost presentiment studies. Each session of the experiment included both erotic and nonerotic pictures randomly intermixed,and the main psi hypothesis was that participants would be able toidentify the position of the hidden erotic picture significantly moreoften than chance (50%).The hit rate on erotic trials can also be compared with the hitrates on the nonerotic trials to test whether there is somethingunique about erotic content in addition to its positive valenceand high arousal value. For this purpose, 40 of the sessionscomprised 12 trials using erotic pictures, 12 trials using negativepictures, and 12 trials using neutral pictures. The sequencing of thepictures and their left/right positions were randomly determined bythe programming language’s internal random function. The remaining 60 sessions comprised 18 trials using erotic pictures and18 trials using nonerotic positive pictures with both high and lowarousal ratings. These included eight pictures featuring couples inromantic but nonerotic situations (e.g., a romantic kiss, a bride andgroom at their wedding). The sequencing of the pictures on thesetrials was randomly determined by a randomizing algorithm devised by Marsaglia (1997), and their left/right target positions weredetermined by an Araneus Alea I hardware-based random numbergenerator. (The rationale for using different randomizing procedures is discussed in detail below.)Although it is always desirable to have as many trials as possiblein an experiment, there are practical constraints limiting the number of critical trials that can be included in this and several othersexperiments reported in this article. In particular, on all the experiments using highly arousing erotic or negative stimuli, a relativelylarge number of nonarousing trials must be included to permit the3participant’s arousal level to “settle down” between critical trials.This requires including many trials that do not contribute directlyto the effect being tested.In our first retroactive experiment (Experiment 5, describedbelow), women showed psi effects to highly arousing stimuli butmen did not. Because this appeared to have arisen from men’slower arousal to such stimuli, we introduced different erotic andnegative pictures for men and women in subsequent studies, including this one, using stronger and more explicit images fromInternet sites for the men. We also provided two additional sets oferotic pictures so that men could choose the option of seeingmale–male erotic images and women could choose the option ofseeing female–female erotic images.2From the participants’ point of view, this procedure appears totest for clairvoyance. That is, participants were told that a picturewas hidden behind one of the curtains, and their challenge was toguess correctly which curtain concealed the picture. In fact, however, neither the picture itself nor its left/right position was determined until after the participant recorded his or her guess, makingthe procedure a test of detecting a future event (i.e., a test ofprecognition).Results and DiscussionAcross all 100 sessions, participants correctly identified thefuture position of the erotic pictures significantly more frequentlythan the 50% hit rate expected by chance: 53.1%, t(99)2.51,p.01, d0.25.3 In contrast, their hit rate on the noneroticpictures did not differ significantly from chance: 49.8%, t(99)0.15, p.56. This was true across all types of noneroticpictures: neutral pictures, 49.6%; negative pictures, 51.3%; positive pictures, 49.4%; and romantic but nonerotic pictures, 50.2%.(All t values1.) The difference between erotic and nonerotictrials was itself significant, tdiff(99)1.85, p.031, d0.19.Because erotic and nonerotic trials were randomly interspersed inthe trial sequence, this significant difference also serves to rule outthe possibility that the significant hit rate on erotic pictures was anartifact of inadequate randomization of their left/right positions.Because there are distribution assumptions underlying t tests,the significance levels of most of the positive psi results reportedin this article were also calculated with nonparametric tests. In thisexperiment, the hit rates on erotic trials were also analyzed with abinomial test on the overall proportion of hits across all trials andsessions, tested against a null of .5. This is analogous to analyzinga set of coin flips without regard to who or how many are doing theflipping. It is legitimate here because the target was randomlyselected on each trial and hence the trials were statistically independent, even within a single session. Across all 100 sessions, the1I set 100 as the minimum number of participants/sessions for each of theexperiments reported in this article because most effect sizes (d) reported in thepsi literature range between 0.2 and 0.3. If d 0.25 and N 100, the powerto detect an effect significant at .05 by a one-tail, one-sample t test is .80(Cohen, 1988).2In describing the experiments throughout this article, I have used theplural pronouns “we” and “our” to refer collectively to myself and myresearch team.3Unless otherwise indicated, all significance levels reported in thisarticle are based on one-tailed tests and d is used as the index of effect size.453.1% hit rate was also significant by a binomial test (z2.30,p .011).Individual differences. There were no significant sex differences in the present experiment. Over the years, however, the traitof extraversion has been frequently reported as a correlate of psi,with extraverts achieving higher psi scores than introverts. Ameta-analysis of 60 independent experiments published between1945 and 1983, involving several kinds of psi tasks, revealed asmall but reliable correlation between extraversion and psi performance (r .09, z 4.63, p .000004; Honorton, Ferrari, & Bem,1992). The correlation was observed again in a later set of telepathy studies conducted in Honorton’s own laboratory, r.18,t(216) 2.67, p .004 (Bem & Honorton, 1994).The component of extraversion that underlies this correlationappears to be the extravert’s susceptibility to boredom and atendency to seek out stimulation. Eysenck (1966) attributed thepositive correlation between extraversion and psi to the fact thatextraverts “are more susceptible to monotony . . . [and] respondmore favourably to novel stimuli” (p. 59). Sensation seeking is oneof the six facets of extraversion on the Revised NEO PersonalityInventory (Costa & McCrae, 1992), and Zuckerman’s SensationSeeking Scale (1974), which contains a subscale of BoredomSusceptibility, is significantly correlated with overall extraversion(r .47, p .01; Farley & Farley, 1967).To assess stimulus seeking as a correlate of psi performance inour experiments, I constructed a scale comprising the followingtwo statements: “I am easily bored” and “I often enjoy seeingmovies I’ve seen before” (reverse scored). Responses were recorded on 5-point scales that ranged from Very Untrue to VeryTrue and averaged into a single score ranging from 1 to 5.In the present experiment, the correlation between stimulusseeking and psi performance was .18 ( p .035). This significantcorrelation is reflected in the enhanced psi scores of those scoringabove the midpoint on the 5-point stimulus-seeking scale: Theycorrectly identified the future position of the picture on 57.6% ofthe erotic trials, t(41)4.57, p.00002, d0.71, exactbinomial p.00008. The difference between their erotic andnonerotic hit rates was itself significant, tdiff(41) 3.23, p .001,d0.50, with 71% of participants achieving higher hit rates onerotic trials than on nonerotic trials (exact binomial p.003).Their psi scores on nonerotic trials did not exceed chance, 49.9%,t(41)0.08, p.53. Finally, participants low in stimulusseeking did not score significantly above chance on either erotic ornonerotic trials, 49.9%, t(57)0.06 and 49.9%, t(57)0.13,respectively.But is it precognition? The role of random number generators. For most psychological experiments, a random numbertable or the random function built into most programming languages provides an adequate tool for randomly assigning participants to conditions or sequencing stimulus presentations. For bothmethodological and conceptual reasons, however, psi researchershave paid much closer attention to issues of randomization.At the methodological level, the problem is that the randomfunctions included in most computer languages are not very goodin that they fail one or more of the mathematical tests used toassess the randomness of a sequence of numbers (L’Ecuyer, 2001),such as Marsaglia’s (1995) rigorous Diehard Battery of Tests ofRandomness. Such random functions are sometimes called pseudorandom number generators (PRNGs) because they use a mathe-BEMmatical algorithm to generate each subsequent number from theprevious number, and the sequence of numbers is random only inthe sense that it satisfies (or should satisfy) certain mathematicaltests of randomness. It is not random in the sense of beingindeterminate because once the initial starting number (the seed) isset, all future numbers in the sequence are fully determined.In contrast, a hardware-based or “true” RNG is based on aphysical process, such as radioactive decay or diode noise, and thesequence of numbers is indeterminate in the quantum mechanicalsense. This does not in itself guarantee that the resulting sequenceof numbers can pass all the mathematical tests of randomness,however; some hardware-based RNGs also fail one or more of thetests in the diehard battery (L’Ecuyer, 2001). Both Marsaglia’sown PRNG algorithm and the true hardware-based Araneus AleaI RNG used in our experiments pass all his diehard tests.Note that a random number table is actually a PRNG, even if thesequence of numbers was originally generated by a true RNG.Once the table is printed or stored electronically and an entry pointinto the table is chosen, the resulting sequence is fully determined,with the entry point being equivalent to the seed number of acomputer-based PRNG.At the conceptual level, the choice of a PRNG or a hardwarebased RNG bears on the interpretation of positive findings. In thepresent context, it bears on my claim that the experiments reportedin this article provide evidence for precognition or retroactiveinfluence. In the experiment just reported, for example, there areseveral possible interpretations of the significant correspondencebetween the participants’ left/right responses and the computer’sleft/right placemen…