meaning. This is a highly replicable result and has served as the basis for literally hundreds of published studies of reading, semantic memory effects of brain damage on cognition, and so forth. The important point here is that accuracy measures do not reveal the effect of having just processed an associated word (Shoben 1982). This is a common result in studies of cognition—accuracy measures are not precise enough to demonstrate the often small, but very important, effects studied.
The implications of this analysis for psi should be obvious. Perhaps the repeated failure to find evidence for psi is due to the almost universal use of a dependent measure that is just too crude to find the looked-for effects. With this in mind, my students and I (Hines and Dennison 1988; Hines, Lang, and Seroussi 1987) conducted a series of studies of psi using reaction time as a dependent measure.
One study (Hines and Dennison 1988) followed naturally from Schmidt’s work described above. On each trial a computer generated, randomly, a 0 or a 1. In the ESP condition, this digit was stored in the computer’s memory. The computer then generated another random 0 or 1 and displayed that digit on a television monitor in front of the subject. The subject had to decide, as quickly as possible, if the digit on the screen was the same as the digit stored in the computer’s memory or not. Reaction time, measured from the onset of the digit on the monitor to the time the subject responded, was recorded, as was the accuracy of the subject’s responses.
Even if ESP is a real phenomenon, the accuracy measure would be unlikely to demonstrate it. Previous studies have failed to provide any adequate evidence for ESP when accuracy measures have been used. In line with this prediction, our subjects performed no better than chance when the accuracy measure was used. The real test, however, was the much more sensitive reaction time measure. If ESP exists, subjects should respond more quickly when they are correct than when they are incorrect. Whatever the source of the hypothesized extrasensory information, if it were getting to the brain, where it would have to be processed to have any effect at all on behavior, it would speed up the process of making a correct decision. However, we found no difference between correct and incorrect reaction times that even approached statistical significance, nor did providing feedback to the subjects regarding their accuracy on each trial change these results. Reaction times of correct and incorrect responses remained the same.
We also examined a precognition condition, again with and without feedback to subjects on their accuracy. In the precognition condition, the computer generated a random 0 or 1 and displayed it on the monitor. The subject then had to decide if the digit the computer would generate after he or she responded would be the same as or different from the one on the screen. After the subject responded, the computer generated another 0 or 1. As in the clairvoyance condition, subjects were no more accurate than expected by chance, nor were they any faster when their responses—predictions, in this condition—were correct than when they were incorrect. Again, the presence or absence of feedback to the subject did not alter this pattern.
In another study, Hines, Lang, and Seroussi (1987) adapted the lexical decision task described above to the study of ESP. There were two conditions. In both the control and the ESP conditions, a subject made a series of lexical decisions on letter strings presented on the right side of a television monitor controlled by a computer. In the control condition, the lone subject had no companion. In the ESP condition, there was a second subject who made decisions about letter strings presented on the left side of the television monitor. The two subjects sat on opposite sides of a divider that prevented either from seeing the other or the other side of the monitor. In the ESP condition the subject who sat on the left side of the divider—the agent or “sender”—saw a letter string, and 400 milliseconds later the receiver—the subject on the right side of the screen—saw a letter string. Both subjects had to make lexical decisions on the letter strings they saw. On some of the trials in the ESP condition, the letter string the agent saw was the same one the receiver saw, 400 milliseconds later. In the standard lexical decision task, if the same subject sees the same letter string twice in a row, reaction time on the second presentation is greatly reduced. This is due to the fact that the location in memory that stores the concept, if the string is a word, is activated by the first presentation and when the same word occurs again, that location is much more able or ready to be activated again. This activation decays after a few seconds. If, then, there is extrasensory communication between individuals even of a very low level, it should show up in the reaction times of the receiver when the agent had just processed, 400 milliseconds previously, the same letter string that the receiver was processing. We found no hint of any such effect in our data.
Failure to find an effect is not conclusive evidence that the effect is not real. However, the fact that several of our studies using a highly sensitive reaction time measure have consistently failed to show any evidence for psi seems to be convincing prima facie evidence against the reality of the phenomena.
Psi phenomena of one sort or another have been systematically studied for more than one hundred years. This century of investigation shows a common, repeating pattern. A new phenomenon or method is found that “finally shows that psi is real,” the skeptic is told. However, upon careful examination, the claim collapses. But by the time one claim has been carefully investigated and found faulty, another phenomenon or method has come along that, “once and for all, shows psi to be real.” And on it goes. First there was spiritualism, then card-guessing experiments, then individual psychics like Geller, then the ganzfeld studies, and now the random events studies of Schmidt and others.
It is important to realize that, in one hundred years of parapsychological investigations, there has never been a single adequate demonstration of the reality of any psi phenomenon. Why, then, does the field of parapsychology continue to exist? Why has it not withered away, like the study of N rays and polywater? I think that there are two major, and not unrelated, reasons. First, especially since the early 1960s, parapsychology has acquired a following that is made up of people—most of them not active investigators and most with almost no scientific training—who accept the reality of psi not because of any empirical evidence, but simply because psi fits well with their view of what the world and reality ought to be like. This is a world in which the spiritual dominates over the scientific and rational; a world in which simply thinking good thoughts can make the world “right” again; a world in which what one feels to be true is, automatically and without effort, true; a world where there is no need to carefully consider evidence to arrive at the truth. At present, I suspect that this group is quite large and helps to support the enormous number of uncritical books, television programs, and newspaper articles about psi and other aspects of the paranormal. Thus, these topics are kept in the public eye. This, in turn, fuels the interest of the general public and helps to support parapsychological research, both in terms of funding and in terms of the publicity that is so rewarding to researchers in any field.
The second reason for the persistence of parapsychology as a discipline has to do with the type of logical arguments permitted within the field. The use of the nonfalsifiable hypothesis is permitted in parapsychology to a degree unheard of in any scientific discipline. To the extent that investigators accept this type of hypothesis, they will be immune to having their belief in psi disproved. No matter how many experiments fail to provide evidence for psi and no matter how good those experiments are, the nonfalsifiable hypothesis will always protect the belief. The investigator will thus persist in conducting experiment after experiment, even when none of them produces positive results. The nonfalsifiable hypothesis always permits, almost requires, the attribution of the experiments’ failures to something other than the nonexistence of psi. This attitude is epitomized in the quotation from Rogo (1986) earlier in this chapter regarding the reasons for Blackmore’s failure to find any evidence of psi in her numerous experiments. Rogo didn’t even consider the possibility that psi doesn’t exist. Rather, he put forth the totally untestable idea that Blackmore’s failure to find evidence of psi was due to her deeply hidden, unconscious motives. In any other area of scientific research, it would be impossible for anyone to seriously propose such an “explanation” for the failure to find a hypothesized effect. The type of reasoning so frequently used in parapsychology, reasoning that is nearly invulnerable to empirical disproof, is much more characteristic of religion than of science. Alcock (1985) has persuasively argued that for many, but certainly not all, parapsychologists, the search for psi has become an almost religious quest, a quest to dethrone materialistic science and reestablish the dominance of a spiritual approach to the world.
PSI THEORY AND BELIEF
Many theories have been proposed by parapsychologists to explain how psi takes place. To skeptics, such theory building seems premature, as the phenomena to be explained by the theories have yet to be demonstrated convincingly. The theories cover a wide range of proposed mechanisms (see Rao 1978, for an excellent review). At one end of the spectrum, there are theories that implicitly accept the “transmission hypothesis” of psi, according to
