miércoles, febrero 16, 2011

La percepción extrasensorial en una revista de la APA

Bem, D. J. (En prensa). Feeling the future: Experimental evidence for anomalous retroactive influences on cognition and affect. Journal of Personality and Social Psychology. [doi] [pdf]

Nota. Esta revista está editada por la asociación de Psicología más importante del mundo y va por el volumen 100. No es, ni mucho menos, una revista de vaya usted a saber dónde.

The 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 not otherwise be anticipated through any known inferential process. Precognition and premonition are themselves special cases of a more general phenomenon: the anomalous retroactive influence of some future 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 the individual's responses are obtained before the putatively causal stimulus events occur. Data are presented for 4 time-reversed effects: precognitive approach to erotic stimuli and precognitive avoidance of negative stimuli; retroactive priming; retroactive habituation; and retroactive facilitation of recall. The mean effect size (d) in psi performance across all 9 experiments was 0.22, and all but one of the experiments yielded statistically significant results. The individual-difference variable of stimulus seeking, a component of extraversion, was significantly correlated with psi performance in 5 of the experiments, with participants who scored above the midpoint on a scale of stimulus seeking achieving a mean effect size of 0.43. Skepticism about psi, issues of replication, and theories of psi are also discussed.

Ejemplo de experimento:

Experiment 1: Precognitive Detection of Erotic Stimuli


One hundred Cornell undergraduates, 50 women and 50 men, were recruited for this experiment using the Psychology Department’s automated online sign-up system. They either received one point of experimental credit in a psychology course offering that option or were paid $5 for their participation. Both the recruiting announcement and the introductory explanation given to participants upon entering the laboratory informed them that
this is an experiment that tests for ESP [percepción extrasensorial]. It takes about 20 minutes and is run completely by computer. First you will answer a couple of brief questions. Then, on each trial of the experiment, pictures of two curtains will appear on the screen side by side. One of them has a picture behind it; the other has a blank wall behind it. Your task is to click on the curtain that you feel has the picture behind it. The curtain will then open, permitting you to see if you selected the correct curtain. There will be 36 trials in all. Several of the pictures contain explicit erotic images (e.g., couples engaged in nonviolent but explicit consensual sexual acts). If you object to seeing such images, you should not participate in this experiment.

Each session of the experiment included both erotic and nonerotic pictures randomly intermixed, and the main psi hypothesis was that participants would be able to identify the position of the hidden erotic picture significantly more often than chance (50%). The hit rate on erotic trials can also be compared with the hit rates on the nonerotic trials to test whether there is something unique about erotic content in addition to its positive valence and high arousal value.


Across all 100 sessions, participants correctly identified the future position of the erotic pictures significantly more frequently than the 50% hit rate expected by chance: 53.1%, t(99) = 2.51, p = .01, d = 0.25. In contrast, their hit rate on the nonerotic pictures did not differ significantly from chance: 49.8%, t(99) = -0.15, p = .56. This was true across all types of nonerotic pictures: neutral pictures, 49.6%; negative pictures, 51.3%; positive pictures, 49.4%; and romantic but nonerotic pictures, 50.2%. (All t values tdiff(99) = 1.85, p = .031, d = 0.19. Because erotic and nonerotic trials were randomly interspersed in the trial sequence, this significant difference also serves to rule out the possibility that the significant hit rate on erotic pictures was an artifact of inadequate randomization of their left/right positions.
Como ustedes comprenderán, el artículo, todavía en prensa, ya he generado una enorme reacción. De hecho, ha conseguido que la discusión entre estadística frecuentista y bayesiana llegue a las páginas de New York Times.

¿Mi opinión? Ah, si tuviera tiempo ahora mismo para tener opiniones... Pero no quería dejar de darles noticia sobre esta serie de experimentos.

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