Precognitive Habituation: Replicable Evidence for a Process of Anomalous Cognition

Precognitive Habituation (PH) is a phenomenon that has emerged from a search for a straightforward laboratory demonstration of psi that could: (a) be observed using participants from the general population; (b) be conducted with no instrumentation beyond a desktop computer; (c) be evaluated by simple statistical tests; and, (d) be replicated by any competent experimenter—including a skeptical one. The PH procedure is based on a well established psychological phenomenon known as the Mere Exposure Effect: Across a wide range of contexts, the more frequently humans or other animals are exposed to a particular stimulus, the more they come to like it. The PH procedure tests for precognition by, in effect, running a Mere Exposure study backwards. Instead of exposing a participant to repeated exposures of a stimulus and then assessing his or her liking for it, the PH procedure reverses the sequence: On each trial, the participant is first shown a pair of photographs on a computer screen and asked to indicate which picture he or she prefers. The computer then randomly selects one of the two pictures to serve as the “habituation target” and displays it subliminally several times. If the participant prefers the picture subsequently designated as the target, the trial is defined as a “hit.” Accordingly, the hit rate expected by chance is 50%. The PH hypothesis is that the repeated exposures of the target can reach back in time to diminish the arousal it would otherwise produce, thereby rendering negatively arousing targets less negative and positively arousing targets less positive. Because the two pictures in each pair are matched for valence and arousal, participants are predicted to prefer the target-to-be on trials with negatively arousing pictures but the non-target on trials with positively arousing pictures (erotic pictures). Preferences on trials with non-arousing (“low-affect”) pictures were not expected to differ from chance. To date, more than 400 men and women have participated in 9 variations of the PH experiment, including an independent replication by a skeptical investigator. Collectively the studies provide strong support for the two predicted effects. Across the six basic studies, the hit rate was significantly above 50% on negative trials (52.6%, t(259) = 3.17, p = .0008) and significantly below 50% on erotic trials (48.0%, t(149) = -1.88, p = .031). When targets were exposed supraliminally, the PH effect was replicated on negative targets but not on erotic ones. Supraliminal exposures also made the experiment more aversive and triggered conscious cognitive processing. When the number of target exposures on each trial increased beyond 8, participants significantly preferred the non-target picture on the low-affect trials. This serendipitous finding appears to reflect “precognitive boredom.” Like a too frequent TV commercial, the repeated exposures (precognitively) render the target boring, or even aversive, and hence less attractive than its matched non-target. Individuals scoring above the median on either Absorption or Openness to Experience appear most likely to show the precognitive boredom effect. Precognitive Habituation 3 Precognitive Habituation: Replicable Evidence for a Process of Anomalous Cognition The holy grail for many psi researchers has long been a straightforward, transparent laboratory demonstration of psi that could be replicated by any competent experimenter—including a skeptical one—using participants drawn from the general population. Discovering such a replicable psi effect and developing a protocol for demonstrating it was the primary goal of the research program described in this article. As a further inducement to replication, I sought to develop a procedure that would require no instrumentation beyond a desktop computer, would take no more than 30 minutes to complete, and could be analyzed with statistics no more complex than a t test across subjects or a binomial test across binary choices. The result of this effort is the Precognitive Habituation (PH) effect. Many psi researchers have advocated the use of physiological or implicit response measures on the grounds that psi probably operates at an unconscious level, and researchers in cognitive and social psychology have recently developed several implicit measures of cognitive and affective functioning that can be adapted for exploring psi. The Precognitive Habituation procedure uses an indirect measure of psi performance that derives from a well-established phenomenon known as the Mere Exposure (ME) Effect. The Mere Exposure Effect Across a wide range of contexts, the more frequently humans or other animals are exposed to a particular stimulus, the more they come to like it. This robust psychological phenomenon has been known for over a century, but it was the 1968 publication of Zajonc’s monograph, “Attitudinal Effects of Mere Exposure,” that spurred its intensive empirical investigation. By 1987, more than 200 experimental studies of the effect had been published. The ME effect is very general. For example, after rats were exposed to musical selections by either Mozart or Schönberg, they showed a preference for new selections by the composer with whom they had become familiar. When tones of two different frequencies were played to two sets of fertile chicken eggs, the hatched chicks preferred the tones they had heard prenatally (Rajecki, 1974). In human studies, individuals exposed differing numbers of times to irregular polygons, nonsense words, Chinese ideographs, photographs of faces, or real people came to like better those to which they had been exposed more frequently; that is, liking was a positively increasing function of exposure frequency. A meta-analysis of 208 such studies by Bornstein (1989) yielded a combined effect size (r) of .26, with a combined z of 20.80 (p < .0000001). This same metaanalysis revealed that the ME effect is stronger when the stimuli are exposed subliminally, that is, at such short exposure times that they cannot be identified. This is interpreted as showing that the ME effect works at an unconscious level and that conscious cognitive processes actually interfere with the primitive affective process presumably responsible for the effect. The ME effect was first employed as a vehicle for testing psi by Moulton (2000). Using a procedure designed to test for telepathy between a sender and receiver, Moulton showed the sender 10 irregular polygons with the instruction to try transmitting them to the remote receiver who was undergoing ganzfeld stimulation, a form of reduced sensory input. After the 30-minute sending period, the receiver was shown ten pairs of polygons in which one polygon of each pair Precognitive Habituation 4 was one that had been seen by the sender. The receiver was asked to indicate which of the two polygons he or she liked better. As predicted, receivers significantly preferred the polygons seen by the sender. The ME effect is typically tested and observed with stimuli that are initially affectively neutral (e.g. polygons, nonsense words). This is also reflected in theorizing about the effect. For example, Zajonc himself (2001) has proposed that the effect reflects a form of classical conditioning that occurs when a novel stimulus is encountered repeatedly in the absence of aversive consequences; it is that absence which plays the role of the unconditioned stimulus. For my own precognitive studies, however, I wanted to use stimuli that are strongly arousing, reasoning that repeated exposure to such stimuli would produce affective habituation: Negatively arousing stimuli would subsequently be experienced less negatively and positively arousing stimuli would be experienced less positively. Curiously, there were no ME studies that had used high valenced or highly arousing stimuli. A recent non-ME study however—reported after my own studies were in progress—has now confirmed this reasoning. Participants subliminally exposed to extremely positive and extremely negative words subsequently rate those words as less extreme than words to which they had not been exposed: Negative words are rated less negatively and positive words are rated less positively (Dijksterhuis & Smith, 2002). The Precognitive Habituation Procedure The Precognitive Habituation procedure tests for precognition by, in effect, running a Mere Exposure study backwards. Instead of exposing a participant to repeated exposures of a stimulus and then assessing his or her liking for it, the PH procedure reverses the sequence: On each trial, the participant is first shown a pair of photographs on a computer screen and asked to indicate which picture he or she prefers. The computer then randomly selects one of the two pictures to serve as the “habituation target” and displays it subliminally several times. If the participant prefers the picture subsequently designated as the target, the trial is defined as a “hit.” Accordingly, the hit rate expected by chance is 50%. The Precognitive Habituation hypothesis is that the repeated exposures of the target can reach back in time to diminish the arousal it would otherwise produce, thereby rendering negatively arousing targets less negative and positively arousing targets less positive. Because the two pictures in each pair are matched for valence and arousal, participants are predicted to prefer the target-to-be on trials with negatively arousing pictures but the non-target on trials with positively arousing pictures (erotic pictures). Preferences on trials with non-arousing (“lowaffect”) pictures were not expected to differ from chance. These studies complement the “presentiment” studies reported by Bierman and Radin (Bierman & Radin, 1997; Radin, 1997). In their studies, participants show an anticipatory electrodermal response just prior to the presentation of negatively arousing or erotic pictures but not prior to the presentation of neutral or low arousing pictures. If we interpret the presentiment effect as the precognitive elicitation of arousal, we can analogously interpret the PH effect as the precognitive extinction of arousal. One advantage of the PH procedure is that it makes opposite predictions for the two kinds of stimuli, whereas the presentiment procedure does not. This article reports eight PH experiments done in my psi laboratory at Cornell University and one external replication by a skeptical investigator. Additional external replications are currently in progress. Precognitive Habituation 5 Method Overall Experimental Procedure During the course of this project, several variations of the experiment were explored. The separate studies differed primarily in the exact instructions given the participant, the number of trials of different types (negative, erotic, and low-affect or “control” trials), the number of exposures of the target, and the specific pictures used. Except where noted, all the experiments used the following general procedure. Upon entering the laboratory, the participant was told: In this experiment, we are interested in measuring emotional reactions to a wide variety of visual images in a procedure that tests for ESP (Extrasensory Perception). The experiment is run completely by a computer and takes about 20–25 minutes. Each trial of the experiment involves a pair of pictures. First you will be shown the two pictures side by side and asked to indicate which one you like better. You will then be asked to watch passively as those pictures are flashed rapidly on the screen. The way in which this procedure tests for ESP will be explained at the end of the session. Most of the pictures range from very pleasant to mildly unpleasant, but in order to investigate a wide range of emotional content, some of the pictures contain very unpleasant images (e.g., snakes and bodily injuries), and some contain nonviolent but explicit sexual content (e.g., couples engaged in explicit sexual activity). The participant then signed a consent form which repeated the warning about the nature of the stimuli. Next, the experimenter seated the participant in front of the computer and withdrew from the cubicle. The cubicle was dimly lit by a floor lamp positioned so that there were no reflections on the computer screen. Overhead fluorescent lights were turned off. The computer program then proceeded to administer the procedure as outlined above, displaying a pair of pictures on each trial, recording the participant’s preference, and then subliminally displaying the randomly selected target several times. At the end of the session, the computer displayed the percent of hits achieved on the different types of trials, and the experimenter interpreted this feedback as part of the post-experiment explanation of the study. Experimental Materials The pictures used in the studies were selected from the International Affective Picture System (IAPS; Lang & Greenwald, 1993), a set of 820 digitized photographs that have been rated on 9-point scales for valence and arousal by both male and female raters. For the PH studies, the pictures were divided into six categories defined by crossing 3 levels of valence (negative, neutral, positive) with 2 levels of arousal (low, high). The negative pictures were drawn from the negative/high arousal category. Although some of the erotic pictures were drawn from the positive/high arousal category, the erotic pictures in the IAPS are quite mild. Accordingly, we supplemented them with more graphic erotic pictures downloaded from the Internet. The remaining pictures were drawn from the other categories of pictures and are henceforth referred to as the low-affect pictures. The pictures in each pair were matched for valence and arousal using the ratings supplied with the IAPS set; they were also matched for Precognitive Habituation 6 content. As the experimental program proceeded, we were increasingly able to match the pictures within pairs for their popularity as well. In most of the PH studies, the targets were exposed subliminally. To qualify as subliminal, a stimulus must normally be flashed with an exposure time of approximately 4 milliseconds. This is not easily achieved on a computer screen, however, because the screen itself is refreshed much more slowly (1/60 second or about 17 ms on slower monitors). Unless the exposure is synchronized with the screen refresh—a difficult programming task—it may not appear on the screen at all. There are two common strategies for overcoming this problem: Backward masking and parafoveal exposure. In backward masking, a masking stimulus is flashed immediately after the image appears, effectively “erasing” the image from the retina. In parafoveal exposure, the participant focuses on a spot in the center of the screen while the images are presented randomly on either the left or the right side of the screen (and, hence, to the side of the fovea). Using both these procedures, we were able to expose the images for 17 ms without the participant’s being able to identify them more than occasionally. It should be noted, however, that the validity of the PH effect as a psi phenomenon is not jeopardized by the possibility that participants might be able to identify the target because the computer does not select it until after the participant makes the preference judgment. In fact, experimental Series 300, reported below, used clearly identifiable exposures of 500 ms duration.