Hypnosis workshop materials

Here are the materials I used in the VIP Hypnosis Workshop of 4 December. Feel free to use the induction MP3s, but please do not listen to these tracks while driving, operating a nuclear power plant, performing brain surgery, or doing anything that requires you to be awake. The Power of Boring is strong is these tracks. The background sound has been generated using http://www.naturesoundfor.me.

Slides: Hypnosis workshop

Induction with backing track:

Reversal with backing track:

Recording of my Quantum Mind lecture (12 Nov)

Last week, I have given a lecture for the VIP, our student association, on my not-at-all controversial work and ideas on consciousness, quantum physics, and psi. Thanks to Jeffrey Harris, who made an audio recording, you can now listen to my waffling, whilst looking at the pdf with slides!

Slides: Quantum Mind


Part 1: Philosophy of Consciousness and the Hard Problem

Part 2: Introduction to Quantum Mechanics, in particular the Measurement Problem

Part 3: The Quantum Mind?

Is psi truly impossible?

Over the last weeks, several interesting posts in which psi prominently featured were posted on the web: one by Alex Holcombe, in which he argues that as long as meta-analyses find evidence for psi, our scientific publication system is broken; one by Sam Schwarzkopf in which he replies to a paper by Bem et al. finding new evidence for psi (that will be published in some time in the future; the study has not been conducted yet); and a satirical poster by Arina Bones, in which she argues that Bem’s presentiment effects were actually rather weak compared to the unlikely results tyically published in JPSP…

Now, to be fair, the mentioned blog posts primarily address methodological issues in (mainstream) science, rather than going into the theory of psi, but the posts have one thing in common: psi is implicitly or explicitly assumed to be impossible, because physics! But is psi indeed incompatible with physics?

Some interesting facts

Before going into that question, I’d like to share two interesting pieces of information. Yes, science is broken, and our publication process is largely to blame for it. The fact that we can find evidence for a phenomenon that is allegedly impossible is, according to Holcombe, a tell-tale sign of this. Two important suggestions to improve our practices are preregistration and using Bayesian rather than frequentist statistics. Interestingly, though, psi researchers seem to have a head start in improving their practices. The European Journal of Parapsychology, for example, has offered the option to preregister research, and have a paper accepted on basis of preregistered methods, independent of the actual outcome  since the late 1970s. It was big news in the psychology community when the journal Cortex started offering this service – only last year…

Moreover, the use of Bayesian statistics is presently advocated strongly by ‘professional skeptics’ to stop the surge of spurious research results (including, but not limited to psi). Interestingly, the idea to use Bayesian statistics in psi is not new. The Journal of Scientific Exploration, a journal notorious for “advocating pseudoscience”, published a critical review of psychokinesis research that explicitly called for the use of Bayesian statistics in the analysis of psi data, because, and I quote, “… a small p-value may not provide credible evidence that an anomalous phenomenon exists”. This paper was published in 1990, almost 25 years ago…

What I’d like to state with this: parapsychology as a research field is controversial, and that its topics, theories and results may be outrageous, but that some of its practices may be exemplary for mainstream psychology.

Psi and physics

Anyway, enough about meta-methodology. Time for some physics. Is psi indeed incompatible with physics? Well, yes and no. Psi effects apparently violate basic laws of physics, either because they involve a reversal of the flow of time (e.g. precognition/presentiment) or a direct influence of one body on another without a mediating force (psychokinesis). But which laws are violated?


First, can information travel back into time (often referred to as retro-causality)? There are two often-heard arguments against this idea: first, the Second Law of Thermodynamics gives time a specific direction or arrow; second, the Special Theory of Relativity (STR) states that nothing can go faster than the speed of light, which would be required if one would want to send information back into time.

I’ve argued before that the Second Law of Thermodynamics does not necessarily imply retro-causality is impossible – only that it is impossibly unlikely. So, what about this idea that nothing can go faster than light? Well, that’s not entirely correct. The only thing that Einstein proposed is that c (the speed of light) is invariant in all frames of reference of space-time. What follows from the STR is that in order to accelerate matter moving at sub-lightspeed beyond c, one would require an infinite amount of energy. Likewise, to decelerate particles moving faster than light (‘tachyons’) to sub-lightspeed  would also require an infinite amount of energy. So yes, for all practical purposes, nothing can go faster than light, but STR does not strictly forbid v > c.

Moreover, c is only constant within frames of reference. Between frames of reference, speeds exceeding c are permitted. However, this does not mean that retro-causality exists. In particular the ‘causality’ in retro-causality is problematic: in STR, causal relations can only exist between an object and objects in its past light cone (i.e., the points in space-time from which you can potentially see a photon emitted by the object). Even though velocities larger than c are permitted, this does make retro-causality in STR a no-no.

However – there may be a loophole. Or several, actually. Physically speaking, the direction of time is rather arbitrary. Without going into too much detail, there are several interpretations of electrodynamics (in particular the Wheeler-Feynman Absorber Theory) and quantum mechanics (two-state vector formalism and Cramer’s transactional interpretation) that explicitly assume time symmetry. Wheeler-Feynman’s absorber theory, for example, deals with the question why radiation seems to be emitted rather than absorbed. Maxwell’s equations for electromagnetic fields always yield two solutions: one going forward in time, and one going backward in time. We typically discard this latter solution, but for no good theoretical reason. Wheeler and Feynman have tackled this problem by assuming that the waves going backward in time are cancelled out (‘absorbed’) at a macroscopic scale. Dick Bierman has proposed that some retrocausal effects may be explained by assuming that the ‘cancelling out’ of advanced waves (‘information from the future’) has gone astray in some case, in particular when consciousness is involved (paper to be found here).

Speculative? Sure. Impossible? No.

Quantum waffling?

So, we don’t even need quantum physics to save the day, but let’s have a closer look. Quantum physics, with all its strange features, is often invoked when trying to explain more mysterious aspects of psychology, in particular consciousness and paranormal phenomena. An often-heard argument against this practice is that it is simply explaining one thing we do not understand (eg., consciousness) with another (quantum physics). Moreover, quantum physics and mysterious quantum phenomena such as entanglement and quantum superpositions are believed only to be relevant at a microscopic scale, and are completely washed out in the ‘hot and noisy’ environment that is our brain.

Surely, skepticism towards the all-too-liberal use of quantum physical concepts when explaining is warranted. In fringe and pseudo-science, quantum physics is often distorted and misunderstood. However, the same thing sometimes goes for debunking attempts from skeptics. Let’s look at some (mis)understandings.

(Mis)conception #1: Quantum physics is not relevant in biological systems such as the brain, and therefore irrelevant in the study of psi.

Can we use quantum mechanical concepts in order to explain weird mental phenomena, such as psi, or even consciousness itself? No, the skeptic argues – the brain is too hot and noisy to allow for any quantum physical phenomenon, such as entanglement or superposition, to occur. Quantum physics is only relevant when studying tiny particles in isolated systems!

Both these assumptions are not entirely correct. To start with the former, empirical evidence is accumulating that quantum processes (in particular quantum coherence) do play a role in living systems, for example in photosynthesis. Direct evidence of quantum processes in the brain still lacks, though. However, it may not be completely inconceivable that quantum processes do play a role in brain functioning. Does that open up the possibility for all kinds of spooky actions at a distance in human cognition? Well, that’s a really, really long stretch. For starters, the fact that quantum effects have been observed in plants does not mean plants are conscious entities that can do telepathy, precognition, and psychokinesis. Second, and more importantly, our understanding of the relation between brain processes at the microscopic scale and cognition is still quite limited. It is very difficult to imagine how quantum processes that play at the scale of single cells or even individual receptor sites would influence cognition and behaviour. However, simply stating that quantum physics by definition has no role in human brain function is not appropriate, I’d say.

Second, is quantum physics only relevant for studying microscopic isolated systems? No. Quantum physics is the best description of reality we have. There is no theoretical limit that states why we cannot describe macroscopic objects in the ‘language’ of quantum mechanics, Actually, we could consider classical Newtonian physics as a special case of quantum mechanics. The discrepancy between the quantum and classical world is rather an empirical observation we do not yet completely understand- there is not a theoretically prescribed boundary of at what scale we should start to use either classical or quantum mechanics to describe Nature. This brings us to a philosophical problem in physics: the measurement problem. According to some (controversial) interpretations of quantum physics (in particular the Von Neumann-Wigner interpretation), consciousness has a special statues in physics, because it ‘collapses the wave function’. I will not go into all specifics here, as this is a blog post, not an article (yet), but this is rather significant: if consciousness is instrumental to a basic physical process, this means it cannot be reduced to physical processes, or more specifically, brain activity. From this point of view, whether or not quantum physical processes play a role in brain processes is a completely irrelevant issue.

As I argued earlier, I think the most pressing reason to study psi is that demonstration of psi would falsify physicalism – the assumption that we can reduce consciousness to physical processes. We all too easily make this assumption when talking about consciousness, even to such an extent that we forget that it is an assumption. Back to psi – many psi effects could in theory be explained if we assume that ‘mind’ or ‘consciousness’ can be directly entered as a system in equations. The calculations would still work – however, the interpretation of the calculations would be rather outrageous… And whilst we’re on that page…

(Mis)conception #2: Quantum physics allows for free will, telepathy, psychokinesis, absolute idealism,  Chopra-ism, etc.!

So, quantum physics, in some interpretations at least, gives us a ‘loophole’ to escape Newtonian determinism – we can have a free will, and if the Von Neumann-Wigner interpretation is correct, we can even ‘create’ reality with our minds!

Er… no.

For starters, quantum physics is probabilistic in nature. Even if consciousness does collapse the wave function, the outcome of that collapse (e.g., finding a particle at a given location or not) will be completely random and unpredictable. As I argued in an earlier blogpost, that is not a very desirable feature of free will, or reality shaping in general. So, I would say free will and creation of reality are safely out of the scope of quantum mechanics.

So, what about psi? For the sake of argument, let’s assume quantum effects are somehow related to psi. Suppose that psi effects are the result of quantum entanglement: you, the observer, become entangled with a physical system far away in space and/or time, and for some reason something happens to the distant system. This means it would affect you instantaneously, because you and the distant system are entangled. However, quantum weirdness can never be used to communicate information at supraluminal speeds, which would be needed for causal psi. In quantum information theory, there is such a thing as the no-communication theorem. In order to make sense of the non-local interaction that happened (or even be aware that something happened at all), you need to correlate your state with the state of the distant system. This correlation can only be done via ‘classical’, sub-luminal communication.

This rules out any kind of ‘causal’ psi. With this I mean that quantum-based psi cannot be used to change your behaviour to avoid a given future, for example (i.e., the Final Destination scenario). What may exist in this framework, though, are correlational effects, such as proposed and reported by Von Lucadou and Walach.

Does psi violate physics?

Well, as it seems, not necessarily. There are interpretations of physics that do allow for psi-like effects to occur. However, these interpretations are not your main-stream ones, and do take some background in physics to fully comprehend. As physics laymen, we as psychologists/neuroscientists are often tempted to dismiss any interpretation that falls outside the ordinary stuff we learnt in high school or undergraduate physics courses. Perhaps rightfully so. However, stating that psi is impossible because physics? Hm, I’d be very careful with making that statement. Best not to calibrate our statistical methods using a phenomenon that actually might exist after all…

Scientists build Rube Goldberg machine, sell it to press as Brain-to-Brain Interface

Have you seen this study? It made headlines all over the world – first direct brain-to-brain interface! Brain activity of one person is recorded, decoded and sent over the internet to a computer which controls a brain stimulator, which in turn stimulates another person’s brain! Sounds quite sci-fi, right?!

Well, I hate to spoil the fun, but apart from a pretty cool demonstration of two well-established techniques in cognitive neuroscience, this study literally tells us nothing about brain function we did not already know, nor leads to any practical application in the (near) future. Besides – it’s not even new. Andrea Stocco and Ranesh Rao did almost the exact same thing over a year ago. Both these ‘brain-to-brain’ interfaces are hardly spectacular, however, not even as a proof-of-concept. At best, they are the neuroscientist’s equivalent of a Rube Goldberg machine. Fun art projects,  not science.

So, what’s going on? Brain-computer interfacing, or BCI, refers to the decoding of brain activity in realtime and transform this into a control signal. BCI has been around for a while, and there are several reliable ways to use brain activity to generate control signals. The P300 is an example – ‘P300’ refers to a positive peak in the electroencephalogram that occurs roughly 300 ms after an observer spots something that captures her/his attention. The P300 is widely used as a dependent measure in cognitive neuroscience and psychophysiology, and can be detected in single events with quite a good accuracy. So, if you are monitoring a participant’s brain responses to particular events, finding a P300 tells you that the this event captured the participant’s attention. You can use this, for example, to guess someone’s PIN code: let a participant hold his PIN code in mind, and flash the numbers 0 – 9. The numbers that evoke that largest P300s are likely to be in his/her PIN code. How to get to the full PIN code, I leave up to your own imagination and evil genius…

However, there are more benevolent applications. P300s are used widely to drive spelling programmes for patients with different kinds of disabilities. However, the P300 is a passive measure: it’s something your brain does in response to an external stimulus. Ideally, for BCI applications, you want a measure you as a user can have some control over. Motor imagery is increasingly used to generate control signals. If you think of moving your arm, this generates activity in a specific part of the motor cortex. Think of moving your foot, and you activate another part of your motor cortex. With EEG you can pick this up and discriminate between different imagined movements with high accuracy. My colleague Ritske de Jong has developed algorithms that pretty much work out-of-the box and are up to 99% accurate. Once you know what movement a participant is imagining, converting that to a control signal is trivial. Both Rao and Stocco, and Grau et al. use this type of BCI for their Rube Goldberg machines.

But what about the brain stimulation part? In the brain-to-brain interfacing studies, researchers use transcranial magnetic stimulation (TMS) to induce brain activity. TMS is a very useful tool to study brain functioning because it allows us to interfere with brain processes. You cannot just disrupt brain processing though – stimulating the motor cortex can lead to (rather jerky) movements, and stimulating the occipital cortex results in seeing a flash of light, a phosphene. In order to stimulate a given area, you simply position your coil over that area. However, that is as sophisticated as it gets. You can induce a jerky movement, or you can induce a very brief lasting phosphene with TMS. You cannot influence someone’s thoughts, or fine-tune someone’s actions with TMS, apart from annoying your participants.

Both this ‘first’ demonstration of a brain-to-brain interface and the actual first demonstration of a brain-to-brain interface use TMS to stimulate the brain of the receiving participant. And it’s exactly this what makes me characterize it as Rube Goldberg machines. The sophistication of the computer-to-brain interface is about that of hitting someone with a hammer. There is simply nothing practical that you can do with TMS, as opposed to implanted electrodes. Even worse, there is reason to believe that TMS has a theoretical limitation in terms of what kind of brain activity and brain areas can be stimulated. It is very unlikely that TMS or any other kind of non-invasive brain stimulation will ever have the level of sophistication to induce brain activity at the fine-grained level required to control thoughts and actions.

So, what do both brain-to-brain studies, that are supposedly ‘proofs-of-concept’, show? Well, they show that:

  • you can use BCI to generate a control signal. Great, we already know that for quite a while.
  • you can transmit this control signal via the internet. Well, that’s obvious too, you wouldn’t reading this blog if we could not signals via the internet
  • you can use a control signal to trigger a TMS device. Since TMS devices are around, they can be triggered by a TTL-pulse… so this is not really new, too…

All in all, there is really nothing new or surprising in these studies. There are no fundamental issues that are resolved, or new technological insights that truly show a new way of getting information from one brain into another. The setups presented in these studies are really nothing more than Rube Goldberg machines – hilariously complicated setups to perform a task that can be solved much, much simpler.

But they do make cool demonstrations. It’s just not science.

Oh, and as for brain-to-brain interfacing… what about this?


On (social) priming

Hmm, never thought (micro)blogging would be such an interesting experience… turns out it’s an excellent way to be exposed to different views and opinions. Last week, I posted an unpublished manuscript and dataset in which we attempted to make people behave more prosocially after priming them with eyes, an effect which has been originally published by Haley and Fessler in 2005, and conceptually replicated by Bates, Nettleson and Roberts in 2006.

I did not set out to directly replicate this effect, and to test its existence. Rather, I was interested in putting my theories on conscious versus unconscious perception to the test. In several papers, but most importantly Jolij and Lamme, 2005 we found that people can respond to unconsciously processed visual information (‘blindsight’), but only do so when they are in ‘guessing mode’. I proposed that this may the result of ‘repression’ of unconscious information.

What does this have to do with priming? Well, here I explain why I think sometimes we do, and sometimes we do not find blindsight. The idea is that unconscious information processing is great, but may be inaccurate. Since our behavior is so easily influenced by all kinds of external stimuli (yes, I was a firm believer in ‘social’ priming!), you don’t want any inaccurate information influencing you, and therefore the cognitive system represses the inaccurate information it gets from the unconscious visual pathway (most of the time).

To test that idea, we came up with the experiment I posted last week. We took a ‘social’ priming effect, and manipulated prime visibility by masking the primes. Our prediction was that priming would not work for masked primes. And that came out! Sadly, the priming effect was also absent for the visible primes. After running several studies, totaling almost 400 participants, I gave up. I simply could not find any reliable evidence for the effect I was looking for, not with tokens, not with study credits, not with money,  not with questionnaires. Now, all this was in 2008-2010.

After an inspiring talk by Zoltan Dienes about half a year ago (see here) I went through my archives to see if there might be anything there I could analyse with his methods and found this dataset back. I ran a Bayes factor analysis, and found that the Bayes factors were informative, and yielded substantial evidence for the null hypothesis of no effect. In other words: in the presented dataset it’s not just a null-effect, it’s actually 5.26 times more likely there is no effect of eye primes in this context than that there is. Given that there apparently was information in the data, despite a fairly low N (although nicely in line with your average priming experiment), we decided to give it a try and publish it.

Admittedly, with today’s knowledge, I tried to capitalize somewhat on the debate on social priming, and it turns out one sentence in particular was found somewhat offensive by some:

The lack of a firm theoretical background, problems with statistical power, potentially flawed methodology [6, 7], the exposure of several high-profile studies as fraudulent [8, 9], but most importantly, repeated failures to directly replicate several effects [10-13] has led to strong skepticism towards the notion of social priming.

In all fairness, I do think this statement is accurate. There is skepticism towards ‘social’ priming, and the reason for that is that quite some direct replications have failed, and that QRPs and fraud have been uncovered in others. Most importantly, though, we have yet to see a solid explanation as to why we sometimes do, and sometimes do not get these effects.

But the problem is: what is ‘social priming’ in the first place?

On the ISCON Facebook page, Jeff Sherman once mentioned that all priming (both ‘cognitive’ and ‘social’) is priming, because it’s all about priming behavior. Norbert Schwarz jokingly defined ‘social priming’ as ‘priming cognitive psychologists cannot replicate’.

Now, both of  these statements are obvious oversimplifications. One of the problems plaguing the ongoing debate on priming is the lack of a clear taxonomy of what comprises different kinds of priming, and indeed, I myself have been guilty of not properly defining what I mean with ‘social priming’ in the manuscript I posted last week.

So, let me give you my 2c  on the matter. I agree with Jeff Sherman to most extent. Priming is the modification of processing of subsequent stimuli and behavior by a given prime stimulus. Period. What distinguishes ‘cognitive’ from ‘social’ priming in my understanding (which, arguably, may be totally wrong) is mainly the length and complexity of the processing chain between prime and behavior. In what we call ‘cognitive’ priming, the chain is short. The archetypical ‘social priming’ study typically relies on a long chain of events between prime and behavior.

In most priming effects I typically employ in the lab, it’s about visuomotor transformations. In a task in which participants have to respond to the direction of an (target) arrow, presenting another (prime) arrow in the same direction, responses to the target will be faster, even if the prime is masked. This can be quite easily explained in terms of decision thresholds, or biasing processing of visual input. Several studies have shown direct communication between visual and motor areas in such tasks, and modulation of baseline motor activity by primes – in other words, as long as there is some direct visuomotor transformation, we can actually map the effect of our primes on brain activity in real time. I can pinpoint and measure the different subprocesses (perceptual encoding in the visual cortex between 80 ms and 100 ms, plus a second stage around 200-300 ms, decision making in the parietal cortex, starting around 100 ms, and  motor preparation in the motor areas, from 200 ms after stimulus onset, etc.) and study these independently. In other words: I know what’s going on.

However, when I am priming people with eyes to make them behave more prosocially, I do not. I can come up with a decent chain of events, though. From fMRI studies, we know that eyes are processed in dedicated areas of the visual system, and we know that prosocial behavior (in particular in ultimatum and dictator games) is mediated by the right dorsolateral prefrontal cortex from several fMRI and TMS studies. I can well imagine a modulation of the DLPFC by eye cues, only this has not been shown (yet). And maybe it will not be, because there is no such thing – I don’t know. At least, it can be tested.

For embodiment-type priming effects, it differs. There are pretty well-understood effects: take for example the SNARC-effect: if you have to respond to a number, you’re faster responding with your left hand than your right hand when the number is small, but vice versa when the number is large. This is a quite robust effect, attributed to the automatic activation of a ‘mental number line’. We typically order numbers from left to right: 1, 2, 3, 4, etc. In other words, magnitude of a number has a direct relation with spatial cognition. Indeed there is pretty good converging evidence from fMRI and TMS studies that a fronto-parietal spatial cognition network plays a critical role in number magnitude processing.

Interestingly, there is also evidence these spatial cognition networks underlie perception of social distances. This allows me to do a very specific prediction: if you prime someone with the concept ‘close’, and subsequently ask for this judgment about his social distance to someone, this should result in ‘closer’ judgments then when you prime someone with the concept ‘far away’. I am aware that Williams and Bargh did this in 2008, and indeed found this effect, but unfortunately they used a pretty poor priming strategy, and not surprisingly Pashler et al (2012) failed to replicate the effect. What’s needed as a prime is ideally a distance judgment task in 3D (so how far an object is from you) that really draws on spatial processing, rather than drawing two dots that are either close to each other or separated.

Now, the longer the association chain becomes, the more ‘line noise’ there may be, and the less credible effects become at first sight. Take for example the pee-study by Tuk et al. (this one) claims that a full bladder leads to increased impulse control, allegedly because having a full bladder requires the ‘inhibitory’ parts of the brain to prevent you from peeing, which at the same time inhibits making impulsive decisions. A bit far-fetched, but ok. I can see this work. Your brain gets somatosensory feedback from the sphincter muscle of your bladder, but you need to put in effort to hold in your wee, which allegedly activated the cognitive control circuits of your brain. This does not automatically imply that all behavior is subsequently inhibited of course. Sadly, the authors have missed out on a great opportunity to test their explanation (their study 3 is hardly convincing for their argument): why not do a task that measures response inhibition, in a ‘full bladder’ and ’empty bladder’ condition, within-subject, of course?

It’s quite easy, really. You can do an anti-saccade task (in which participants have to suppress the urge to make an eye movement to a suddenly appearing target). If the authors are correct, one should expect better performance in the bladder-full than in the bladder-empty condition. N=30 to 40, with at least 200 – 300 trials per participant should do the trick. An experiment like this can be run in about a week.

Now,  where things get quite dubious for me as a cognition researcher is the authors’ claim that priming participants with words that have to do with urination produce similar effects on behavioral inhibition. The chain of necessary events here is very long. First, it assumes that reading a word related to peeing (such as toilet, watering, etc.) activates a semantic network related to urination. Ok. There’s evidence for that. Point granted. Second, that semantic activation somehow results in a greater awareness of an urge to pee. Maybe. If you draw attention to a bodily function, participants will be more aware of it. This increased awareness leads to an actual increased urge to pee. Good, they actually tested that, and found an effect. Subsequently, this leads to increased inhibitory control (not tested), which leads to less impulsive behavior.

Notwithstanding my doubts, combining this type of priming with an anti-saccade task may be used to prove or disprove their hypothesis. Again, if seeing the word ‘urine’ activates inhibitory systems, we would expect an improvement on anti-saccade performance after priming participants with pee.

To cut a long story short, what I miss in a lot of priming research is a justification of all the individual assumptions that are made in order to explain the priming effect observed. If we can actually be more specific about these assumptions, and test them, we might actually get somewhere.

So, why not work together and figure out what’s really going on? If anyone is interested in the distance, or pee-studies, let me know, or if you know of a priming manipulation which I could use in stead of eye priming for the study that kicked this off, please get in touch!


Making people nicer with eye primes does not work – always.

Quick update here – I got some questions about this study, and to clarify some things:

  • this study is not a direct replication, nor is it intended as a replication. Rather, I was interested in putting my ideas on unconscious perception to the test: based on earlier work, I predicted that priming prosocial behaviour would only work for unmasked stimuli, and not for masked stimuli. Turned out the priming effect did not work for either condition.
  • Because it was not a replication attempt, I did not stick to Simonsohn’s N*2.5 rule. Nevertheless, Bayes factors turned out to be informative, and yield substantial evidence for the null.
  • Did I expect the effect to replicate? Sure as hell I did! The data published here is only our final attempt. In total, we tested almost 400 participants between 2008 and 2010, but since this was all ‘before Stapel’, and there was no effect in the data, I have been sloppy with the earlier data. This dataset, collected by Tineke de Haan for her MSc-thesis, is complete and well-documented; the other data I got in is not. Otherwise I could have presented a huge dataset without any effect. A second experiment, in which we looked at effects of eye primes on responses on questionnaire that measures moral behaviour (N=90), also – no effect at all. If you’re interested in that data, let me know.The only reason I kept on trying is because I truly believed the effect would be there, because it’s so plausible!
  • Is ‘social priming’ anything I expect not to replicate? Nonsense. See new blog post in the making for that one.

Darn, some bad news for the weekend. A paper I submitted to PLOS One got rejected. But in all fairness, it was a non-successful conceptual replication with so many potential moderators that it’s hard to draw any conclusions. We (that is, my master student and I) decided to try to publish it anyway, in line with this paper by Jelte Wicherts et al., but the editor disagreed.

So, too bad, but I can live with this rejection.

However, since I do not have time to shop around to try and get it published somewhere else, but at the same time would like to save the rest of the world interested in making people nicer with eye primes (masked and unmasked) some time, I uploaded the data to PsychFileDrawer, plus as a bonus, the full manuscript and data can be downloaded from this very website.

The manuscript can be found here, the data here. Comments of course welcome via e-mail!

Why no one will win the Randi or Chopra Challenges

Whoa! Deepak Chopra is offering 1 million dollars to anyone able to present a falsifiable theory of consciousness, in response to James Randi’s $1 Million Dollar challenge to show paranormal (psi) effects exist! Of course, Twitter and Facebook are going bonkers over this. And I have been going a little bit bonkers over all the responses, to be frank. Just to blow off some steam, here are my thoughts on Chopra’s challenge, and the responses to it.

First of all, many people responded to Chopra’s call with sarcasm and cynicism, and made fun of Chopra’s lack of understanding of science.

It struck me how many of these people lack any understanding of science themselves, but I guess that’s Twitter for you. I’d like to say to these people who ‘fucking love science’: proclaiming yourself an atheist or tweeting ‘WOO WOO’ to @jref does not make you a scientist any more than making a coherent sentence with the words “quantum”, “universal”, and “spirit”.

 So, what’s this all about? Years ago, James Randi, a professional stage magician, and renowned skeptic put out a 1 million dollar prize to any individual able to show true ‘paranormal’ ability. Anyone who would be able to read the future, do telekinesis, or make money as Ghostbuster, Randi would pay one million dollars. To date the prize remains unclaimed.

Deepak Chopra, on the other hand, is an Indian MD who writes books on consciousness and quantum mysticism using the Deepak Chopra Quote Generator, and apparently makes enough money to throw a million dollars at anyone coming up with a falsifiable theory of consciousness.

Neither of these challenges make sense.

Randi’s challenge does not make sense because it operates on a straw man argument: it makes a caricature of psi and then shoots at it. No, there are no such things as seeing in the future, telekinesis, or mind reading. No matter how sad it makes me to admit this, Professor X and Jean Grey DO NOT EXIST (come on, you all at least fantasized about being able to read minds and get the remote and/or your beer and pizza without having to leave your couch!) Period. Does not work, cannot work – not according to the laws of physics, not according to present theories on psi. What might exist, though, are weak, anomalous effects that if they exist, may only be detected in high-powered studies involving a large number of subjects set up in a very specific manner, that need to be pre-registered, and replicated, and replicated again before we can even start drawing conclusions about the existence of psi. So, no individual will ever be able to show paranormal ability, and thus claim the Randi prize. Safe bet, Mr. Randi.

Chopra’s challenge makes no sense because it is horribly ill-defined. Coming up with a falsifiable scientific theory of consciousness is not possible without properly defining ‘falsifiable’ and ‘consciousness’. What Chopra means to say is he will give a million dollars to anyone who can come up with a falsifiable materialist theory of conscious experience, that is, a theory of the subject of consciousness – the experience itself; not (necessarily) its contents. And that is an impossible challenge, because it is a contradiction in terms. You cannot come up with a falsifiable materialist theory of consciousness, and claim the Chopra prize. Safe bet, Mr. Chopra.

But how does mind relate to matter, then? Why can’t we have a falsifiable theory of consciousness?

I am not going to repeat Introduction to Philosophy of Mind here, but roughly we have four classes of mind/matter-theories:

  1. Only matters exists, mind is an illusion
  2. Mind exists, independent of matter
  3. Mind is dependent on matter (or vice versa)
  4. Only mind exists, matter is an illusion

Now, let’s be good scientists, and shoot at these propositions to falsify them, shall we? Classes 1 and 2 are fairly easy to shoot at, so I’ll use proper bullets 😉 Classes 3 and 4 are somewhat more challenging, though.

Let’s start with 1, which you may call orthodox materialism. It’s easy to debunk (with one caveat, though).

  • Cogito ergo sum. I have conscious experiences. Even if these experiences (including the feeling of being the subject of conscious expriences) are illusions, I am still experiencing these illusions. Therefore consciousness exists – even if all other apparent conscious beings in the universe would be philosophical zombies (that is, beings that act rational, but lack conscious experience).
  • If consciousness exists, there is ‘mind’. This rules out orthodox materialist monism (the notion that there is only matter, and that mind is an illusion).
  • Caveat: I can only falsify this for myself, because I cannot with certainty claim anyone else has conscious experiences. Vice versa, you cannot verify my conscious experiences, so you should not believe my claim, but base your evaluation on your own conscious experience (or lack thereof).

Number 2 is good old Cartesian substance dualism. Let’s shoot!

  • In order to move a body, the mind needs a way to operate it
  • Operating a body requires brain cells to fire
  • In order to make a brain cell fire, energy is required – the mind needs to add energy to the brain in order to make this work
  • Physics (ie our understanding of matter) does not allow the creation of energy within a closed system. How can mind get energy into the brain?
  • The probabilistic nature of quantum mechanics will not save you here, Church of the Quantum Spirit. Quantum mechanics describes physical reality at the finest grained level, and contrary to classical mechanics, which is deterministic in nature, quantum mechanics is probabilistic. In other words: the x(t) = v*t gives the position of a moving object at time (t) with absolute certainty; the Schroedinger equation (or better, a transformation thereof) only gives the probability that a particle will be at a given position at a given time. A typical ‘quantum woo’-argument is that the probabilistic nature of QM potentially allows for a mechanism via which mind can influence matter. However, QM is probabilistic – the outcome of a quantum measurement is inherently unpredictable. That may sound very convenient if you want to believe in free will, but in fact it is a terrible property for a cognitive system, or social beings like us. Our entire social network, and our own mental sanity flourish by the mere fact that we are (in general) quite predictable in our actions and thoughts.  Let’s please not introduce fundamental randomness in there, I’d say…

Classes three and four are more difficult to shoot down. Since WordPress does not allow me to use mortar grenade points, but only bullet points I’ll switch back to full text.

Number 3 is the class of what I call ‘weak monism’. We accept mind and matter exist. However, the one substance is dependent on the other (or: one substance can be reduced to the other). This is the category in which we will find main stream theories of consciousness. Weak monist theories come in two flavours. Materialist (or physicalist) theories propose that mind is the result of physical processes, and can be described as such. The Orthodox Skeptics are adherents of these theories, as are most main stream scientists. Idealist theories state that mind is supreme, and that matter is created by the mind. Chopra’s Church of the Quantum Spirit is of this denomination.

Weak monism, though, suffers from the dreaded Hard Problem. How does a change in one substance result in changes in the other? This goes for both materialism and idealism. Materialists need to explain how a change in matter (brain cells) translates into consciousness, and why some physical processes (action potentials) result in consciousness in some circumstances, whereas the same physical process do not in other circumstances. However, also if you’re from the Church of the Quantum Spirit, you have a hard problem. If matter is a result of mind, how come not all mental activity results in changes in matter?

According to many materialists, including Dan Dennett, the Hard Problem is not really a problem at all. Consciousness simply is the sum of all brain activity, period. In slightly more subtle wording: consciousness is believed to be an emergent phenomenon, resulting from the complexity of the neural networks of our brain. This is called supervenience – reality can be described at different levels, and higher levels of description (consciousness, mind) are dependent on features of lower levels of description (brain, neurons). Or, as Kalat has put it in Biological Psychology for generations of psychology students: you can look at the Mona Lisa as a painting of La Giaconda, and talk about in the sense of her mysterious smile, or you can give a detailed descripton of the canvas and pigments used. Same thing, different levels of description. Similarly, mind is the same thing as brain activity, but simply described in different terms. Obviously, we can easily swap around the words ‘mind’ and ‘matter’ to fix the Hard Problem for idealism.

Now, I hate to bring this news to the Orthodox Skeptics, but this is Woo in its purest form. You cannot call any theory that only says ‘if you make something complex enough it becomes conscious’ a serious theory! How complex does a system have to be in order to become conscious? At what level of description does consciousness emerge? Does the physical system need to be a brain, or would any physical system do? In other words – calling consciousness an emergent property of brain activity and leave it at that is hardly any more scientific than declaring universal quantum love and spirit (or insert your favourite Deepak Chopra quantumism here).

There are several problems with the emergence/supervenience theories of consciousness, but I personally think John Searle brought up the best argument against supervenience theories. Let me paraphrase it in terms of the Chinese Room thought experiment: in this thought experiment, we lock up a man who only speaks English in a room. Via a slot in the door he is given sheets of paper with Chinese characters. Using a manual in the room, he is able to look up an appropriate response in English. He writes the reply on another sheet of paper, which he returns via the slot. From the outside, it looks like the man knows Chinese! In reality, of course, he does not. Searle used this to argue that true artificial intelligence does not exist – for example, if you are training a system to respond to a user in natural language, what you’re doing is giving an artificial system a manual. The system does not understand language in the sense we understand language.

The Chinese Room can also serve as a thought experiment on consciousness. Take a system (a body), and pop a computational unit in there  that can map inputs to outputs it (let’s call this magic device a ‘brain’). The brain or parts of it are not conscious in any sense – they simply map inputs to outputs. However, looking at the system, operating in the world, it is conscious, or at least, bears all signs of it. This is pretty much in the line of Alva Noë’s ideas of how consciousness depends on embodiment.

In his book “Intuition Pumps and Other Tools for Thinking”, Dan Dennett defuses Searle’s argument by stating that the thought experiment is flawed. It does not matter if the ‘guy inside’ understands Chinese or not – the system (that is, the room) does. Digging deeper for ‘understanding’ or ‘consciousness’ makes no sense. There is no ‘Hard Problem’ – conscious experience is just what a system is doing at a particular level of description.

Now, I would like to very explicitly state here that Dan Dennett is probably one of the greatest minds alive, and I am nowhere in his league. I am a great fan of his work, and I feel that it should be compulsory reading for any undergraduate in psychology. However, I think he is wrong here. The reason for that? He plays a trick on us in defusing the Chinese Room.

The trick is this: he smuggles in an external observer. The Chinese Room understands Chinese only if observed by and interacting with an external observer. The ‘understanding’ of Chinese by the room only exists in the mind of the observer! Otherwise, the actions of the Chinese Room are meaningless. Likewise, the brain-in-a-body-operating-in-the-world is only conscious if observed in an appropriate context. Following Searle, I do find this problematic. Consciousness is a first-person perspective. I know I am conscious, because I am both subject and object of my experiences. Who or what is then describing the activity of my brain-body in such a way it enables my first person consciousness? It cannot be me because I am the result of this observation, and unless we allow paradoxical cause-effect relations (which I doubt any materialist would be very keen of), we are left with a very urgent question: in whose mind do I exist?

In sum, I see pretty big problems with materialist theories of consciousness. However, converting to idealism does not solve the problem. As argued earlier, idealism also suffers from the Hard Problem, and the above analysis applies as well. The Hard Problem is deviously difficult to defuse if you accept that mind and matter exist .

One possible solution is to give consciousness a ‘fundamental’ status. Consciousness is a fundamental property of the universe, like the universal forces. Hameroff and Penrose’s Orch OR model rests on this assumption, but also Giulio Tononi’s highly fashionable and critically acclaimed IIT 3.0 model of consciousness puts as its ‘zeroth’ postulate ‘consciousness exists‘. In a recent online article, Christof Koch even explicitly explored panpsychism (the idea that everything is conscious) as a solution to the mind-body problem. However, this does not explain why consciousness exists. And given that physicists are not satisfied with merely stating that ‘gravity exists’, we as psychologists should not be satisfied with stating that ‘consciousness exists’.

Anyway, in a rather large nutshell, this is why the Chopra Challenge makes no sense. Apart from the fact it is poorly defined, we are nowhere near an empirically verifiable (or falsifiable) theory of consciousness. All we’re doing now and have been doing since the era of brain scanning is looking for neural correlates of consciousness, which is a very useful enterprise because it provides boundary conditions for consciousness, but we have not been cracking on the Hard Problem at all. The Hard Problem is probably fundamentally unsolvable within a weak monist framework. In itself this does not prove Chopra right, of course.

On a separate note: what would advance our understanding is a potential falsification of  the idea that mind can be reduced to matter. This is actually the reason I started doing psi research, apart from my lifelong wish of being a Ghostbuster when I finally grow up. If we can convincingly demonstrate that certain aspects of mental functioning cannot be reduced to physical processes, we would have a strong case to either revise our physical models, or falsify materialism. Given the potentially huge impact of psi research, and the fact that the present corpus of data does not allow for clear falsification of psi, I think it is a very worthwhile area of research. But that’s my 2c.

Oh, we have one class of theories left, don’t we? Absolute idealism or monist idealism states that only mind exists, and that matter is an illusion. Well, to quote Sherlock Holmes, “when you have eliminated the impossible, whatever remains, however improbable, must be the truth.” 😉

Woo woo…


PS regarding my last point, I can recommend reading Schroedinger’s “What is Life?” It is a short book, which you can read in a couple of hours, but will stay with you for a lifetime. Yes, I know I stole that quote from the reviews of the book, but it’s very true.

Social priming and psi

Update: before being accused of being a bully because I compare social priming researchers to parapsychologists, a) I consider myself to be a psi researcher, so if anyone takes offense to being compared to myself, I am very sorry, and b) the bottom line of this post is: if you take social priming seriously based on the empirical record, you should take psi seriously, too.

Now, there you have two controversial terms in one blog post title! No, I am not going to claim that psi may be involved in social priming or vice versa. No, I won’t make any claims here about paranormal phenomena playing a role in social priming (although…), but something struck me when going over my Twitter feed this weekend.

So, what happened? Well – sh*t really hit the fan after publication of Social Psychology’s replication issue, edited by Brian Nosek and Daniel Lakens, to be found here. A lot of things have already been written and blogged on the entire issue of replications and replicating research, and the debate has turned quite ugly from time to time. But I’ll not be addressing that here – many other did a better job at that than me.

No, what struck me is that there seem to be some interesting parallels between parapsychology and social priming research I’d like to share with you. Disclaimer beforehand: I am an active researcher in both social priming and psi. I may be prejudiced with regard to both topics – please keep that in mind when reading 😉

First of all: both fields make bold claims about the nature of the human mind and – if correct – have far-stretching consequences for our understanding of who we are. If psi exists, it would mean the mind does not answer to laws of physics, and may therefore not be reduced to brain activity. Or the laws of physics are wrong, that’s also an option. At least, the confirmed existence of psi would change our view of the world. Your mind is not what your brain does – but something more! That’s an idea many people would find attractive.

Social priming research, if true, shows that our environment has an extremely large impact on our behaviour, both overt and covert – a simple prime may make us walk slower, make us buy stuff we normally would not, or even make us more or less prone to show criminal behaviour. Taken to the extreme (a point once defended by Diederik Stapel in an interview with the Dutch ‘Academische Boekengids’, if you read Dutch, you can find it here), it means that you, or your ‘self’ – the agent that decides what you body will do next – is nothing more than a series of tendencies primed by your environment. Consciousness and free will have little to do with behaviour and are just illusions. Maybe not a pleasant idea, but very tangible – it means that human behaviour is rational, and can be completely explained and understood. Again, an idea many people would find attractive.

So, it’s clear both fields have a large appeal: they challenge our native and naive ideas about who we are. It’s therefore not surprising that both parapsychology and social priming are ‘hot topics’ in the main stream popular media.

Both social priming and parapsychology have a serious problem, though: after a series of spectacular claims and promising results (for parapsychology in the 1930s, for social priming starting in the 1990s), problems arose. Key findings turned out to be difficult to replicate. In parapsychology, there is even a term for this: the decline effect, and it’s even become a topic of study. After some initial successes to demonstrate telepathy, precognition or clairvoyance, effect sizes decreased, to disappear completely after repeated replication attempts. In social priming, we see that the large effects reported by original studies quite often turn out to be far smaller or even non-existent in subsequent replications ran with larger populations. As a result, both fields are struggling to show that the effects they study even exist. Overall, meta-analyses do show there is ‘something going on’, both for psi and social priming, but the actual effects are elusive.

The emphasis on showing effects has drawn attention away from what a mature field should do: come up with theories and test those. Both parapsychology and social priming are traditionally characterized by lack of theories that explain the phenomena that are being studied. And with ‘theories’ I mean a general, and plausible framework that can produce falsifiable claims – not post-hoc explanations for effects. In social priming, for example, I once read a nice metaphor about how behaviour is akin to a piano on a sheet of ice, subject to all kind of external forces – see here) Although this sounds very reasonable, this theory cannot be falsified – if a finding does not replicate, you can always conjure up a ‘moderating’ variable that has extinguished the effect. Another reason that in particular cognitive (neuro)scientists are very critical about social priming research is that the explanations for the effects are very implausible with regard to their (neuro)cognitive implementation.

My greatest concernt, though, is the elusiveness of the effects. I do accept that the effects may exist. I doubt, though, how relevant the effects are in everyday life. In a blogpost, Simone Schnall mentioned an online replication attempt of her (in)famous finding that washing your hands makes you behave more morally. The replication failed. Schnall was not surprised – she explicitly stated that the priming procedure would only work in the lab, where subjects can be closely monitored. This is a pretty strong blow for ecolgical validity – if an effect does not replicate outside the lab, then what does it really tell you about human behaviour?

Parapsychology, though, seems to have matured a bit more than social priming over the last years. There are several falsifiable theories out there that do predict when psi phenomena will occur, and under what circumstances, for example Von Lucadou’s model of Pragmatic Information, and Bierman’s CIRTS-model. Both these models are inspired by physics, and do make sense. Most importantly, they are falsifiable: both MPI and CIRTS make very explicit predictions about psi-effects. According to the MPI, for example, psi-phenomena can be explained as non-local correlations, analogous to quantum entanglement. As in quantum theory, MPI postulates that such non-local correlations can never be used to transmit information – if that were possible, they would allow for faster-than-light communication, and thus for nasty paradoxes. This yields some weird predictions: most importantly, as soon as an effect becomes ‘informative’ it has to disappear. For example, you may be able to find presentiment in one study. However, in the next study you now know that you may expect presentiment, and thus build a presentiment-meter (see my previous post). According to MPI, you’re not allowed to – and, poof, your effect is gone.

So, how to demonstrate psi if it disappears if you’re looking for it? Von Lucadou proposed an elegant solution: don’t look for it specifically. Von Lucadou and co-workers have published several experiments in which they show that in interactions between an observer and a quantum random number generator, the output of the qRNG will correlate with aspects of the observer. However, which aspects cannot be known beforehand. So, the one time, there is a correlation between the qRNG and the observer’s intentions (which would be the classical psychokinesis-case – it looks like you’re influencing a physical system with your mind), the next time it’s a correlation between the qRNG and the observer’s shoe size. The only solid thing is that if you measure, let’s say, 100 correlations, you will always find more than you’d expect on basis of chance alone.

So, to summarize – psi and social priming are both controversial fields, where there is good reason to assume something’s going on – but we don’t know what. Both fields have come up with theories, and parapsychology seems to be doing an even better job than social priming. However, in the end, it’s very well possible both fields are chasing ghosts. Well, if that’s the case, at least the parapsychologists can say it’s their job.

Is psi a legitimate topic of study?

Weird stuff happens from time to time – it’s a fact of life. When I was applying for a position as assistant professor in Exeter, the weeks before the interview the word ‘Exeter’ started to pop up in weird places in my life – newspaper articles, names of conference rooms I happened to present in, stuff like that. Or that time that my then four-year old, right before leaving home, started to talk about the street in front of his school being changed into a river – when we arrived fifteen minutes later we found the street to be flooded by a bursted water pipe.

Coincidence? Probably. Nevertheless, most people will have experienced such weird coincidences, and sometimes people interpret these experiences as ‘paranormal’. Paranormal experiences include clairvoyance, telepathy, precognition, and psychokinesis. Not surprisingly, these phenomena, collectively labelled as ‘psi’, are met with great interest by the general audience, but traditionally, psychologists have been very interested in them as well. William James, the founding father of psychology, studied paranormal phenomena, and the name-giver of our research intstitute, Gerard Heymans, credited as the first Dutch experimental psychologist, was also the founder of the Dutch Society for Psychical Researcy, for example.

However, psi research (or parapsychology) was met with increasing skepticism. The weird experiences we all have from time to time turned out to be very difficult to replicate in laboratory settings, and basically, ever since its inception, parapsychology is struggling to confirm psi even exists, let alone come up with a solid theoretical background. As a result, nowadays, parapsychology is typically considered to be (at best) fringe science, or even pseudoscience, and is actively ignored by main stream psychology.

A small number of researchers have continued parapsychological investigations, though. Rather than aiming for dramatic demonstrations of psi by mediums, for example, modern-day parapsychologists study far more subtle effects. One of the best-studied topics is that of presentiment (see eg. Bierman and Radin, 1997): an anomalous baseline response to a stimulus that yet has to appear. An emotional picture, for example, induces a strong physiological response. In presentiment, this response appears to be temporally mirrored in the baseline: emotional picture evoke a physical reaction before they are presented, and apparently this physiological response is symmetrical in time (i.e., if the typical physiological response occurs at t = 2.5s, the ‘presponse’ will occur at t = -2.5s). Presentiment has been quite widely studied, and the effects seem to be more stable and legit than your typical psi-effect.

Presentiment has drawn wide mainstream attention with the publication of Bem’s landmark 2011 paper ‘Feeling the future’ in JPSP (Bem, 2011). Bem claimed to show solid evidence for the existence of presentiment in a whole series of experiments, in over 1000 subjects. However, the paper was met with a storm of criticism. I am calling Bem’s paper a landmark paper because it can be pinpointed as the paper that started off the massive debate on questionable research practices in (social) psychology, even before the uncovering of the fraud cases of Stapel, Hauser, Smeesters, and (likely) Foerster. The main critique on Bem’s work was that Bem appeared to ‘shop’ in his results, and did not use appropriate statistics: basically, he was accused of practices such as ‘p-hacking’ (mildly massaging your data until you hit p <.05), and ‘HARKing’ (hypothesizing after the results are known). Moreover, replications of Bem’s experiments failed, and the refusal of JPSP to publish these failed replications only added to the uproar surrounding the field of social psychology (one set of null results has been published in PLOS One, though: here).

Bem, however, did not give up. He, and his coworkers, have published two meta-analyses on the presentiment effect. Armed with the statistical techniques used by his critics (such as p-curves and Bayesian analyes), Bem and colleagues analyzed 90 experiments and show that there ‘is something going on’ in their latest meta-analysis, to be found here.

What to make of this? Does Bem’s latest work indeed support the existence of psi? Let me first say that a) I consider myself to be an open-minded skeptic (more on that later), and b) that I am far from an statistics expert. Having reviewed the latest paper I find the case compelling at first sight. I have got two major concerns, though.

1. How big is the file drawer? Bem et al. estimate that the overall effect size they find for psi can only be negated by at least 520 studies finding no effect. At first sight, this seems a large number. But is it really that unlikely that there are 520 experiments yielding no result Bem et al. did not know about and therefore did not include? Well, it is not. The Bem-experiment has drawn wide attention, and is likely to have been replicated. In our own institute several teaching assistants (ie. not academic faculty!) have used the Bem case as example in second year research practicals. Such data is typically not archived, as it is not considered to be ‘research’, and therefore goes unnoticed. Tenured and tenure-track faculty are less likely to engage in direct replications for the ‘usual’ reaons: lack of time, concerns about tenure, or simply lack of interest. In other words, I do not think 520 experiments (worldwide!) is a completely unrealistic number. The file drawer on psi might be quite substantial.

In addition, if they exist, pre-cognitive effects should also emerge in main-stream research. If a stimulus can exert retro-active influence, this should also be apparent in paradigms that are not explicitly designed to measure psi. For example, in a typical priming experiment, one could look at effects of primes (or targets) presented in trials after the critical stimulus. If precognitive effects do exist, one should be able to find effects in such datasets as well. Now, I myself have several datasets in such weird things are going on, although the most parsimonious account is still a main-stream one, obviously. However, ideally, to make a strong case for psi, main-stream research should be taken into account as well.

2. The theoretical background. The Achilles-heel of psi-research, though, is the lack of a clear theoretical framework. Just that you find a difference between two conditions in an experiment does not mean that much: laws of probability dictate you will find a difference in 1 out of every 20 experiments with p<.05. What matters if your difference fits with a given theory: were you able to predict you would find a difference? Many critics argue that parapsychology lacks a theoretical basis, and that given that psi is incompatible with the laws of physics, research into psi is by definition pseudoscience.

And that is where many critics are wrong.

Psi is not necessarily incompatible with physics. Bem et al. drag in quantum physics, which is something more scholars appear to do when stuff gets complicated (I consider it to be a bad habit), but there is no need for quantum physics to find a loophole in physics that allows psi. Psi involves the flow of information backward in time. Perhaps surprisingly, this is not impossible according to physics. Most physical laws are in fact time-symmetric. For example, in the formula x(t) = v * t, which gives the position x of a point mass at moment t given its speed v, there is nothing against entering a negative number for t. The only physical law which imposes a direction of the flow of time is the second law of thermodynamics, which postulates that the entropy of a closed system will increase over time. Basically it means that the sugar cube you put in your coffee will dissolve, but not spontaneously re-appear after it dissolved, and that your coffee will get colder over time, but not hotter (unless you heat it).

This is such a fundamental property of the universe that it dictates a direction of time on all other physical processes. However, it is also not a law, but a statistical property of the universe. Basically, potential high-entropy states of a system are far more abundant than potential low-entropy states. Consider the sugar cube in your coffee: the organized, low-entropy state in which sugar molecules are when packed into a cube is quite specific. All molecules of the sugar cube are packed into a confined spatial location (the cube), which limits the number of possible states. However, molecules of a fully dissolved cube can be anywhere in your mug, yielding a far larger number of possible states. Yet, it is not impossible that a sugar cube will rematerialize in your cup of coffee after dissolving (there is no physical law prohibiting the sugar molecules in your cup of coffee of reassembling themselves into a sugar cube), it is just impossibly unlikely. And to date, we do not know how the universe got itself into this mess – why was entropy at the beginning of everything so low?

That aside – technically, time reversals, or better, the universe adopting a state where effect appears to precede cause, are not impossible, just extremely unlikely. But does it mean that presentiment can be real? Well, there is a second problem. Even if we accept that information in extraordinary circumstances can travel backwards in time, presentiment potentially creates time paradoxes. The best-known example is the grandfather-paradox. Suppose you have a time-travelling machine, and travel back in time to when you grandfather was a child. And you shoot him. Apart from that being quite cruel in the typical circumstance where you have a loving grandpa, it creates a paradox: if your grandfather dies before he fathered one of your parents, how can you exist and travel back in time to shoot him?

The same thing applies to presentiment. Technically, it is possible to build a presentiment detector if the effect is real: Bierman and Radin (1997), for example, report an anomalous increase in galvanic skin response before presentation of an unpredictable emotional stimulus compared with the baseline response to neutral stimuli. If you sample a participants GSR to stimuli for a sufficient number of trials, it is well possible to estimate a participant’s typical baseline to neutral stimuli and estimate whether the baseline response on a given trial is typical of a subsequent neutral or subsequent emotional stimulus. That would allow you to predict the future: by a quick analysis of anticipatory GSR activity you should be able to guess (not perfectly, though) whether the upcoming stimulus will be emotional or neutral. And this is where the paradox arises: if your analysis is quick enough, you can quickly switch of the monitor, blindfold the participant, or even change the upcoming stimulus before the stimulus is presented and thus prevent the participant from seeing the stimulus that would trigger the emotional reaction. Effectively, this is the same as shooting your grandfather in the grandfather-paradox: if you erase or change the event that triggered the presentiment response in the first place, how can it trigger presentiment?

Stephen Hawking has argued that the universe ‘actively resists’ time paradoxes. Bierman (2001, and personal communications) supposes that this is one of the reasons why psi effects are so elusive: as soon as they become informative, and are able to create time paradoxes, they cease to exist. I am not sure if this is the case or not. However, I find the time paradox argument against presentiment compelling – a lot more compelling than the incorrect argument that psi does not fit with the laws of physics.

In their meta-analysis, Bem et al. cite a Bayesian analysis of Bem’s 2011 paper by Wagenmakers et al. In Bayesian statistics, one evaluates the likelihood of evidence gained by an experiment, or set of experiments, relative to the likelihood of the data given a prior hypothesis. Wagenmakers et al. set their prior to 10^20, meaning that they would be convinced of the reality of presentiment if the outcome of an experiment was 10^20 as likely to be found under the hypothesis that psi exists than under the hypothesis that it does not. Bem et al. report a Bayes-factor of 10^9 in favour of the existence of psi. Impressive – but not impressive enough for Wagenmakers et al. Bem et al. argue that a prior of 10^20 is unrealistically and unreasonably high. Well, is it?

Wagenmakers et al. base their prior on the fact that psi is incompatible with the laws of physics. With that argument I do not agree (see above) per se, but I do think the time paradox argument is convincing enough to warrant a very high prior. 10^20 seems not unrealistic or unreasonable in that sense to me

So to conclude: I am open to the possibility of psi. There are no universal laws against it, it is just extremely unlikely. Bem’s meta-analysis is convincing, but to me not convincing enough. It would be far more convincing if Bem et al. could make more specific theoretical predictions about when and how presentiment might occur. They do offer some interesting points – in particular, presentiment seems to be most prominent in ‘fast thinking’ scenarios. Now, that is actually what I would predict as well. If it exists, presentiment is most likely not a ‘conscious’ phenomenon. Personally, I have never consciously experienced a time-symmetric emotion. However, most of us will know the experience of a ‘gut feeling’ (“I knew something bad was gonna happen!”) My own research has shown that such ‘gut feelings’ are easier picked up when you’re not consciously trying to ‘listen’ to them. So, in that respect, if presentiment exists, it might indeed be easier to find it in experiments that require ‘fast thinking’.

One final remark: some critics argue that psi should not be studied at all, and ridicule any serious treatment of the topic. I have even seen some tweets arguing that psi is an excellence benchmark for novel statistical methods – if you find evidence for psi using your statistical method, your method is wrong!

This stance seems profoundly unscientific to me, in particular coming from people who claim to have strong dislike for pseudoscience. You simply cannot and should not dismiss results purely on the basis that they do not fit your beliefs. I’d say we have some bad experiences with that in the Middle Ages.

Arguably, the theoretical case for psi is not strong, but it is strong enough to take seriously. As a researcher, I study consciousness, and to be frank, we haven’t got a clue how consciousness works. The hard problem of consciousness is still far from solved, and there are profound philosophical problems with the materialist theories of consciousness. Psi (if it exists) may offer new insights into the nature of consciousness. For me, this is the main reason to regard the field with interest and not dismiss is right out of hand. In that respect, I think Bem’s work is valuable, interesting, and deserves recognition from main stream science, and I’d rather have skeptics trying to shoot at the data and analyses than actively ignoring psi altogether. Therefore, I am happy to see that many people have taken a critical look at the data; in the end, this can only give us a clearer picture of what is going on.