Social media and the challenge of managing disagreement positively

Technological change often entails social change. Historically, many of these changes were unintended and could not be foreseen at the time of making the technological advances. For instance, the printing press was invented by Johannes Gutenberg in the 1400s. One can make the argument that this advance led to the reformation within a little more than 50 years and the devastating 30-years war within another 100 years of that. Arguably, the 30-years war was an attempt at the violent resolution of fundamental disagreements – about how to interpret the word of god (the bible), which had suddenly become available for the masses to read. Of course the printing press was probably not sufficient to bring these developments about, but one can make a convincing argument that it was necessary. Millions of people died and the political landscape of central Europe was never quite the same.

Which brings us to social media. I think it is safe to say that most of us were surprised how fundamentally we disagree with each other as to how to interpret current events. Previously, the tacit assumption was that we all kind of agree about what is going on. This is obviously no longer possible and often quite awkward. Social media got started in earnest about 10 years ago, with the launch of Twitter and the Facebook News Feed. Since then, people have shared innumerable items on social media and from personal experience, one can be quite surprised how different other people interpret the very same event.

Which brings us to my research.

Briefly, people can fundamentally disagree about the merits of any given movie or piece of music, even though they saw the same film or listened to the same clip.

Moreover, they can vehemently disagree about the color of a whole wardrobe of things: Dresses, jackets, flipflops and sneakers. Importantly, nothing anyone can say would change anyone else’s mind in case of disagreement and these disagreements are not due to being malicious, ignorant or color-blind.

So where do they come from? When ascertaining the color of any given object, the brain needs to take illumination into account, a phenomenon known as color-constancy. Insidiously, the brain is not telling us that this is happening, it simply makes the end-result of this process available to our conscious experience. The problem – and the disagreement – arises when different people make different assumptions about the illumination.

Why might they do that? Because people assume the kind of light that they usually see, and this will differ between people. For instance, people who get up and go to bed late will experience more artificial lighting than those who get up and go to bed early. It stands to reason that people assume to happen in the future what they have experienced in the past. Someone who has seen lots of horses but not a single unicorn might misperceive a unicorn as a horse, should they finally encounter one. This is what seems to be happening more generally: People who go to bed late do assume lighting to be artificial, compared to those who go to bed early. 

In other words, prior experience does shape our assumptions, which shapes our conclusions (see diagram).

Conclusions can be anything that the brain makes available to our conscious experience - percepts, decisions, interpretation. Objects above dashed line are often not consciously considered when evaluating the conclusions. Some of them might not be consciously accessible. Note that this is not the only possible difference between individuals. Arguably, it might be that the brains are also different from the very beginning. That is probably true, but we know next to nothing about that. Note that differing assumptions are sufficient to bring about differences in conclusions in this framework. That doesn't mean other factors couldn't matter as well. Also note that we consider two individuals here. Once more than two are involved, the situation would be more complicated yet.

Conclusions can be anything that the brain makes available to our conscious experience – percepts, decisions, interpretation. Objects above dashed line are often not consciously considered when evaluating the conclusions. Some of them might not be consciously accessible. Note that this is not the only possible difference between individuals. Arguably, it might be that the brains are also different from the very beginning. That is probably true, but we know next to nothing about that. Note that differing assumptions are sufficient to bring about differences in conclusions in this framework. That doesn’t mean other factors couldn’t matter as well. Also note that we consider two individuals here. Once more than two are involved, the situation would be more complicated yet.

If this is true more generally, three fundamental conclusions are important to keep in mind, if one wants to manage disagreement positively:

1. There is no point in arguing about the outcomes – the conclusions. Nothing that can be said can be expected to change anyone’s mind. Nor is it about the evidence (what actually happened), as the interpretation of that is colored by the assumptions.

2. In order to find common ground, one would be well advised to consider – and question – the assumptions you and others make. Ideally, it would be good to trace someone’s life experience, which is almost certain to differ between people. Of course, this is almost impossible to do. Someone’s life experience is theirs and theirs alone. No one can know what it is like to be someone else. But pondering – and discussing – on this level is probably the way to go. Maybe trying to create common experiences would be a way to transcend the disagreement.

3. As life experiences are radically idiosyncratic, fundamental and radical disagreements should be expected, frequently. The question is how this disagreement is managed. If it is not managed well, history suggests that bad things might be in store for us.

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My policy on quote review

I understand the need of journalists to simplify quotes and make them more palatable to their audience. Academics have a tendency to hedge every statement. In fact, they would have to be an octopus to account for all the hands involved in a typical statement. From this perspective, it is fair that journalists would try to counteract this kind of nuance that their audience won’t appreciate anyway. However, I’m in the habit of choosing my words carefully and try to make the strongest possible statement that can be justified based on the available evidence. If journalists then apply their own biases, the resulting statements can veer into the ridiculous. So I’m now quoted – all over the place – saying the damnedest things, none of which I actually said. Sometimes, the quote is the opposite of what I said. This is not ok.

Of course you can write whatever you want. But that doesn’t include what I allegedly said. Note also that I did give journalists the benefit of the doubt in the past. But they demonstrably – for whatever reason, innocent or willful – did not care much for quote accuracy.

Thus – from now on, I must insist on quote review prior to publication. This is not negotiable, as my reputation is on the line and – again – I’m in the habit of speaking very carefully. This policy is also mutually beneficial – wouldn’t any journalist with integrity be concerned about getting the quotes right?

In the meantime, one should be wise to assume the media version of Miranda: “Everything you don’t say will be attributed to you anyway.”

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Retro-viral phenomena: The dress over and over again

It is happening again. Another “dress”-like image just surfaced.


As far as I can tell, more or less the same thing is going on. Ill defined lighting conditions in the images are being filled in by lighting assumptions, and they differ between people due to a variety of factors, including which light they have seen more of. Just as described in my original paper.

As we get better at constructing these (images with ill-defined illumination), I expect more of these to pop up periodically. But people now seem more comfortable (and less surprised) by the notion that we can see colors of the same image differently.

The reason these things are still a thing is our tacit assumption that we all more or less see the same reality as everyone else.

So if I’m right (which most people presume) and someone else disagrees, they have to be wrong, for whatever reason. Color stimuli like this seem to produce categorically and profoundly differing interpretations. Which is what makes them so unsettling.

I think the same thing – more or less – applies to social and political questions. We take our experience at face value and fill the rest in with assumptions that are based on prior experience. As people’s experiences will differ, disagreements abound.

Which is why I find these stimuli so interesting and which is why I study them in my lab.

Hopefully, as these become more common, it will make people more comfortable with the notion that they can fundamentally – but sincerely – disagree with their fellow man.

Because people operate experientially. Here, they experience benign disagreement. In contrast to politics, where the disagreement is often no longer benign.

So this kind of thing could be therapeutic.

We could use it.
















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Of psychopaths, musical tastes, media relations and games of telephone

Usually, I publicly comment on our work once it is published, like here, here or here.

So I was quite surprised when I was approached by the Guardian to comment on an unpublished abstract. Neuroscientists typically present these as “work in progress” to their colleagues at the annual Meeting of the Society for Neuroscience, which is held in Washington DC in November, this year and at which our lab has 5 such abstracts. Go to this link if you want to read them.

Given these constraints, the Guardian did a good job at explaining this work to a broader audience, emphasizing its preliminary nature (we won’t even attempt to publish this unless we replicate it internally with a larger sample of participants and songs) as well as some ethical concerns inherent to work like this.

What becomes apparent on the basis of our preliminary work is that we can basically rule out the popular stereotype that people with psychopathic tendencies have a preference for classical music and that we *might* be able to predict these tendencies on the basis of combining data from *many* songs – individual songs won’t do, and neither will categories as broad as genre (or gender, race or SES). To confirm these patterns, we need much more data. That’s it.

What happened next is that a lot of outlets – for reasons that I’m still trying to piece together – made this about rap music and a strong link between a preference for rap music and psychopathic traits.

As far as I can tell, there is no such link, I have never asserted there to be one and I am unsure as to the evidentiary basis of such a link at this point.

It is worth pointing out that I actually did not say most of the things I’m quoted as saying on this topic, or at least not in the form they were presented.

So all of this is a lesson in media communications. Between scientists and the media, as well as between media and media, media and social media and social media and people (and all other combinations).

So it is basically a game of telephone: What we did. What the (original) media thinks we did. What the media that copies from the original media think we did. What social media thinks we did. What people understand we did. Apparently, all these links are “leaky” or rather unreliable. Worse, the leaks are probably systematic, accumulating systematic error (or bias) based on a cascade of differential filters (presumably, media filters by what they think will gain attention, whereas readers will filter by personal relevance and worldview). 

Given that, the reaction of the final recipient (the reader) of this research was basically dominated by their prior beliefs (and who could blame them), dismissing this either as obviously flawed “junk science” or so obvious that it doesn’t even need to be stated, depending on whether the media-rendering of the findings clashed with or confirmed these prior beliefs.

Is publicizing necessarily equal to vulgarizing?

I still think the question of identifying psychopaths based on more than their self-report is important. I also still think that doing so by using metrics without obvious socially desirable answers like music taste is promising, e.g. given their lack of empathy, psychopaths could be taken by particularly lyrics or given their need for stimulation, particular rhythms or beats could resonate with them more than average. But working all that out will take a lot more – and nuanced – work.

And to those who have written me in concern, I can reassure you: No taxpayer money was spent on this – to date.

If you are interested in this, stay tuned.

Posted in In eigener Sache, Science, Social commentary | 2 Comments

Vector projections

Hopefully, this will clear up some confusions regarding vector projections onto basis vectors.



Via Matlab, powered by @pascallisch






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What should we call science?

The term for science – scientia (knowledge) is terrible. Science is not knowledge. It is simply not (just) a bunch of facts. The German term “Wissenschaft” is slightly better, as it implies a knowledge creation engine. Something that creates knowledge, emphasizing that this is a process (and the only valid one we have as far as I can tell) that generates knowledge. But that doesn’t quite capture it either. Science does not prove anything, nor create any knowledge per se. Science has been wrong many times, and will be wrong in the future. That’s the point. It is a process that detects – via falsification – when we were wrong. Which is extremely valuable. So a better term is in order. How about uncertainty reduction engine? But incertaemeíosikinitiras probably won’t catch on. 
How about incertiosikini? Probably won’t catch on either.

Posted in Pet peeve, Science | 1 Comment

Predicting movie taste

There is a fundamental tension between how movie critics conceive of their role and how their reviews are utilized by the moviegoing public. Movie critics by and large see their job as educating the public as to what is a good movie and explaining what makes it good. In contrast, the public generally just wants a recommendation as to what they might like to watch. Given this fundamental mismatch, the results of our study that investigated the question whether movie critics are good predictors of individual movie liking should not be surprising.

First, we found that individual movie taste was radically idiosyncratic. The average correlation was only 0.26 – in other words, one would predict an astarsverage disagreement of 1.25 stars, out of a rating scale from 0 to 4 stars – that’s a pretty strong disagreement (max RMSE possible is 1.7). Note that these are individuals who reported having seen *the same* movies.

Interestingly, whereas movie critics correlated more strongly with each other – at 0.39 – which had been reported previously, on average they are not significantly better than a randomly picked non-critic at predicting what a randomly picked person will like. This suggests that vaunted critics like the late Roger Ebert gain prominence not by the reliability of their predictions, but other factors such as the force of their writing.

What is the best way to get a good movie recommendation? In absence of all other information, information aggregators of non-critics such as the Internet Movie Database do well (r = 0.49), whereas aggregators of critics such as Rotten Tomatoes underperforms, relatively speaking (r = 0.33) – Rotten Tomatoes is better at predicting what a critic would like (r = 0.55), suggesting a fundamental disconnect between critics and non-critics.

Finally, as taste is so highly idiosyncratic, your best bet might be to find a “movie-twin” – someone who shares your taste, but has seen some movies that you have not. Alternatively, companies like Netflix are now employing a “taste cluster” approach, where each individual is assigned to the taste cluster their taste vector is closest to, and the predicted rating would be that of the cluster (as the cluster has presumably seen all movies, whereas individuals, even movie-twins will not). However, one cautionary note about this approach is that Netflix probably does not have the data it needs to pull this off, as ratings are provided in a self-selective fashion, i.e. over-weighing those that people feel most strongly about, potentially biasing the predictions.

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Revisiting the dress: Lessons for the study of qualia and science

gifBigWhen #thedress first came out in February 2015, vision scientists had plenty of ideas why some people might be seeing it differently than others, but no one knew for sure. Now we have some evidence as to what might be going on. The illumination source in the original image of the dress is unclear. It is unclear whether the image was taken in daylight or artificial light, and if the light comes from above or behind. If things are unclear, people assume that it was illuminated with the light that they have seen more often in the past. In general, the human visual system has to take the color of the illumination into account when determining the color of objects. This is called color
constancy. That’s why a sweater looks largely the same inside a house 
and outside, even though the wavelengths hitting the retina are very different (due to the different illumination). So if someone assumes blue light, they will mentally subtract that and see the image as yellow. If someone assumes yellow light, they will mentally subtract it and see blue. The sky is blue, so if someone assumes daylight, they will see the dress as gold.
Artificial incandescent light is relatively long-wavelength (appearing yellow-ish), so if someone assumes that, they will see it as blue. People who get up in the morning see more daylight in their lifetime and tend to see the dress as white and gold, people who
get up later and stay up late see more artificial light in their lifetime and tend to see the dress as black and blue.

This is a flashy result. Which should be concerning because scientific publishing seems to have traded off rigor with appeal in the past. However, I really do not believe that this was the case here. In terms of scientific standards, the paper has the following features:

*High power: > 13,000 participants

*Conservative p-value: Voluntarily adopted p < 0.01 as a reasonable significance threshold to guard against multiple comparison issues.

*Internal replication prior to publication: This led to a publication delay of over a year, but it is important to be sure.

*No excluding of participants or flexible stopping: Everyone who had taken the survey by the time of lodging the paper for review at the journal was included.

*#CitizenScience: As this effect holds up “in the wild”, it is reasonable to assume that it doesn’t fall apart outside of carefully controlled laboratory conditions.

*Open science: Shortly (once I put the infrastructure in place), data and analysis code will be made openly available for download. Also, the paper was published – on purpose – in an open-access journal.

Good science takes time and usually raises more questions than it answers. This is no exception. If you want to help us out, take this brief 5-minute survey. The more data we have, the more useful the data we already have becomes.

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Posted in Journal club, Neuroscience, Psychology, Science | 5 Comments

Autism and the microbiome

The incidence of autism has been on the rise for 40 years. We don’t know why, but the terrible burden of suffering has spurred people to urgently look for a cause. As there are all kinds of secular trends over the same time period, correlating this rise in autism with corresponding changes in environmental parameters, led to the “discovery” of all kinds of spurious or incidental relationships.

When attempting to establish causal relationships, experimental work is indispensable, but unethical to do in humans.

Now, it has been shown that feeding maternal mice a high fat diet led to social behavioral deficits reminiscent of autism in offspring. These deficits were associated with a disrupted microbiome, specifically low levels of L. reuteri. Restoring levels of L. reuteri rescued social behaviors, linked to the increased production to oxytocin.

I’m aware of the inherent limitations of mouse work (does anything ever transfer?), but if this does (and I think it will – given recent advances in our understanding of the gut microbiome in relationship to mental), it will be transformational, not just for autism. 

Here is a link to the paper: Microbial reconstitution reverses materal diet-induced social and synaptic deficits in offspring.

Posted in Neuroscience, Nutrition, Psychology, Science | 1 Comment

A primer on the science of sleep

I’ve written about sleep and the need to sleep and how sleep is measured before, but in order to foster our #citizenscience efforts at NYU, I want to bring accessible and actionable pieces on the science of sleep together in one place, here.

1. How the brain regulates sleep/wake cycles

2. Regulating sleep: What can you do?

What you can do

What you can do

3. Sleep: Why does it matter?

Sleep matters

Sleep matters

4. What you can do right now if your baby has sleep problems

5. Common sleep myths

6. Sleep is an active process

Sleep is an active process

Sleep is an active process

7. What are sleep stages?

Sleep stages

Sleep stages

Click on the links if you want to read more.

If you’re curious what our marriage between #citizenscience, #datascience and #neuroscience is about, read this.


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Beyond free will

Some say that every time philosophy and neuroscience cross, philosophy wins. The usual reason cited for this? Naive and unsophisticated use of concepts and the language to express them within neuroscience. Prime exhibit is the mereological fallacy – the confusion of the part with the whole (by definition, people see, not the eye or the brain). And yes, all too many scientists are entirely uneducated, but “winning” might be a function of letting philosophy pick the battleground – language – which philosophy has privileged for over 2500 years (if for no other reason than lack of empirical methods, initially). There is no question that all fields are in need of greater conceptual clarity, but what can one expect from getting into fights with people who write just the introduction and discussion section, then call it a paper and have – unburdened by the need to run studies or raise money to do so – an abundance of time on their hands? Yet, reality might be unmoved by such social games. It needs to be interrogated until it confesses – empirically. There are no shortcuts. Particularly if the subject is as thorny as free will or consciousness. See here for the video.

Posted in Neuroscience, Pet peeve, Philosophy | 1 Comment

Explaining color constancy

The brain is using spectral information of light waves (their wavelength mix) to aid in the identification of objects. This works because any given object will absorb some wavelengths of the light source (the illuminant) and reflect others. For instance, plants look green because they absorb short and long wavelengths, but reflect wavelengths in the middle of the visible spectrum. In that sense, plants – that perform photosynthesis to meet their energy needs – are ineffective solar panels: They don’t absorb all wavelengths of the visible spectrum. If they did, they would be black. So this information is valuable, as it allows the brain to infer object identity and help with image parsing: Different but adjacent objects usually have different reflectance properties and profiles. But this task is complicated by the fact that the mix of wavelengths reflected off an object is dependent on the wavelength mix emanating from the light source in the first place. In other words, the brain needs to take the illumination into account when determining object color. Otherwise, object identity would not be constant – the same object would look different depending on the illumination source. Illumination sources can contain dramatically different wavelength-mixes, e.g. incandescent light with most of the energy in the long wavelenghts vs. cool light LEDs with a peak in the short wavelengths. This is not a recent problem due to the invention of artificial lighting. Throughout the day, the spectral content of daylight changes – e.g. the spectral content of sunlight is different midday from late afternoon. If color perceiving organisms didn’t take this into account, the same object would look a radically different color at different times of day. So such organisms need to discount the illuminant, as illustrated here:

Achieving color constancy by discounting the illuminant

Achieving color constancy by discounting the illuminant

The details of how this process happens physiologically are still being worked out, but we do know that it happens. Of course, there are also other factors going into the constant color correction of the image performed by the organism. For instance, if you know the “true color” of an object, this will largely override other considerations. Try illuminating strawberries with a green laser pointer. The light bouncing off the strawberries will contain little to no long wavelengths, but the strawberries will still look red to you because you know that strawberries are red. Regardless of these considerations, we do know that color constancy matters quite a bit, even in terms of assumed illumination in case of #thedress, when the illumination source is ill-defined:

Discounting an assumed illuminant explains what is going on with the dress.

Discounting an assumed illuminant explains what is going on with the dress.

Of course, things might not be as straightforward as that. It won’t always be perfectly clear what the illuminant is. In that case, the brain will make assumptions to disambiguate. A fair assumption would be that it is like the kind of illuminant one has seen most. In most of human history – and perhaps even today – that means sunlight. In other words, humans could be expected to assume illumination along the daylight axis (over the day), which means short-wavelength illumination, which could account for the fact that most people did report to see the dress as white and gold.

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The neuroscience of violent rage

Violent rage results from the activation of dedicated neural circuitry that is on the lookout for existential threats to prehistoric lifestyles. Life in civilization is largely devoid of these threats, but this system is still in place, triggering what largely amounts to false alarms with alarming frequency.

We are all at the mercy of our evolutionary heritage. This is perhaps nowhere more evident than in the case of violent rage. Regardless of situation, in the modern world, responding with violent rage is almost never appropriate and almost always inadvisable. At best, it will get you jailed; at worst, it might well get you killed.

So why does it happen so often, and in response to seemingly trivial situations, given these stakes? Everyone is familiar with the frustrations of daily life that lead to these intense emotions such as road rage or when stuck in a long checkout line.
The reason is explored in “Why we snap” by Douglas Fields. Briefly, ancient circuitry in the hypothalamus is always on guard for trigger situations that correspond to prehistoric threats. Unless quenched by the prefrontal cortex, this dedicated sentinel system kicks in and produces a violent rage response to meet the threat. The book identifies 9 specific triggers that activate this system, although they arguably boil down to 3 existential threats in prehistoric life:

1) Existential threats to the (increasingly extended) physical self (attacks on oneself, mates, family, tribe)

2) Existential threats to the (increasingly extended) social self (insults against oneself, mates, family, tribe) and

3) Existential threats to the integrity of the territory that sustains these selves (being encroached on or being restrained from exploring one’s territory by others or having one’s resources taken from one’s territory).

Plausibly, these are not even independent – for instance, someone could interpret the territorial encroachment of a perceived inferior as an insult. Similarly, the withholding of resources, e.g. having a paper rejected despite an illustrious publication history could be taken as a personal insult.

The figure depicts the rage circuitry in the hypothamalus - several nuclei close to the center of the brain (stylized)

The figure depicts the rage circuitry in the hypothamalus – several nuclei close to the center of the brain (stylized)

Understood in this framework, deploying the “nuclear option” of violent rage so readily starts to make sense – the system thinks it is locked in a life and death struggle and goes all out, as those who could not best these situations perished from the earth long ago, along with their seed.

Of course, in the modern environment, almost none of these trigger situations still represent existential threats, even if they feel like it, such as being stuck at the post office.

In turn, maybe we need to start respecting the ancient circuitry that resides in all of us in order to make sense of seemingly irrational behavior, perhaps even incorporate our emerging understanding of these brain networks into public policy. In the case of violent rage, the stakes are high, namely preventing the disastrous outcomes of these behaviors that keep filling our prisons and that kill or maim the victims.

Read more: Unleashing the beast within

Posted in Neuroscience, Psychology, Science | 1 Comment

Brighter than the sun: Introducing Powerscape

Statistical power needs are often counterintuitive and underestimated. This has deleterious consequences for a number of scientific fields. Most science practitioners cannot reasonably be expected to make power calculations themselves. So we did it for them and visualized this as a “Powerscape”, which makes power needs immediately obvious.



Read more here:

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Tracking the diversity of popular music since 1940

This is a rather straightforward post. Our lab is doing research on music taste and one of our projects involves sampling songs from the Billboard Hot 100. It tracks the singles that made it to the #1 in the charts in the US (and for how long they were on top), going back to 1940.

Working on this together with my students Stephen Spivack and Sara Philibotte, we couldn’t fail to notice a distinct pattern in the diversity of music titles over time. See for yourself:

Musical diversity over time. Note that the data was smoothed by a 3-year moving average.

Musical diversity over time. Note that the data was smoothed by a 3-year moving average. A value of just above 10 in the early 40s means that an average song was on top of the charts for over 4 weeks in a row. The peak levels in the mid-70s mean that the average song was only on top of the charts for little more than a week during that period.

Basically, diversity ramped up soon after the introduction of the BillBoard charts, and then had distinct peaks in the mid-1960s, mid-1970s and late 1980s. The late 1990s peak is already much diminished, ushering in the current era of the unquestioned dominance of Taylor Swift, Katy Perry, Rihanna and the like. Perhaps this flowering of peak diversity in the 1970s, 1980s and 1990s accounts for the distinct sound that we associate with these decades?

Now, it would of course be interesting to see what drives this development. Perhaps generational or cohort effects involving the proportion of youths in the population at a given time?

Note 1: “Diversity” as literally “number of different songs over a given time period”. The temporal difference density. It is quite possible that these “different” songs are actually quite similar, but there is no clear metric by which to compare songs or a canonical space in which to compare them. Pandora has data on this, but they are proprietary. So if you prefer “annual turnover rate”, it would probably be more precise.

Note 2: My working hypothesis as to what drives these dynamics (that are notable phase-locked to decade) is some kind of overexposure effect. A new style comes about that coalesces at some point. Then, a dominant player emerges, until people get bored of the entire style, which starts the cycle afresh. A paradigmatic case as to how decade-specific the popularity of music is would be Phil Collins.

Note 3: Similarity of music might be hard to quantify objectively. Lots of things sound similar to each other, e.g. the background beat/subsound in “Blank space” and the background beat/subsound in the Limitless soundtrack.

Posted in Science, Social commentary | 4 Comments

Mary revisited: The Brian problem

Generations of philosophers have been fascinated what has been termed the “Mary problem“. In essence, Mary is the worlds foremost expert on color vision and knows everything that there is to know about it. The catch is that she is (depending on the version) either color-blind or has never experienced color before. The question is (depending on the version) whether she is lacking something or whether she would gain new experiences/knowledge if she were to experience color. Supposedly, this is to show us interesting things about physicalism and qualia.

In reality, it only shows us how philosophy is fundamentally limited. The philosophical apperception of the world (as well as interactions among philosophers) is entirely language-based. Needless to say, this is an extremely impoverished way to conceive of reality. Language has all kinds of strange properties, including being inherently categorical. Its neural basis is poorly understood but known to be rather extraneous – most animals don’t have it, and even in the higher primates, most brain regions don’t involve language processing.

Yet, all of Mary’s knowledge is language-based. So yes, if she were to see a color, the part of her visual cortex that processes spectral information (assuming that part of her cortex was intact) would be activated and she would experience the corresponding color, for reasons that are still not well known.

Brian's brain

Brian’s brain

But the heart of the matter – and the inherent shortcomings of an understanding that is entirely language based (invisible to philosophers, as this is something shared by all of philosophy) can be illustrated by a new problem. So let’s add some color to the Mary problem. Here is the Mary problem reimagined: I call this the “Brian problem”:

Brian is the worlds foremost expert on all things sex. He has read every single paper that was ever published in sexology and he also has a keen grasp on the biological and physiological literature. Yet, he has never had sex. Now, Brian has a chance to have sex – would this give him an opportunity to learn anything that he doesn’t already know or have an experience that he didn’t already have? If so, why?

Put in this way, a sample of 100 undergrads were quite clear in their interpretation:

The Brian problem

This nicely illustrates the fundamental problem with language to assess the state of reality: Language has face validity to other people, because it is our mode of thinking, and probably evolved for reasons of social coordination. So arguments might seem compelling (particularly to unrepresentative subcommunities with a shared culture) that do not correspond to an apt description of reality in any other way.

If this is not clear yet: Imagine there being a rat who has never experienced anger but has read every paper on anger. Then you stimulate the ventromedial hypothalamus of this rat with optogenetic methods. Does the rat experience something new? If so, why?

There are really infinite variations of this. Say – for instance – Stephen has read every paper on LSD. He has an intricate understanding of how the drug works. He knows everything there is to know about serotonin receptors and their interactions with ligands. He even understands mTOR, GCaMP and knows everything there is to know about phosphorylation as well as methylation (although that might not be directly relevant). Yet, he has never taken LSD. Now, Stephen is about to take some LSD. Will he experience something that he has not experienced before? Will he learn something? Is this really that hard to understand if one has a lot of prior exposure to philosophical thought?

Posted in Pet peeve, Philosophy | 6 Comments

Pascal’s Pensees, 5 years on

Before October 25th, 2010, I had no social media presence whatsoever – I wasn’t on Twitter, didn’t have a blog and G+ wasn’t around yet. Frankly, it hadn’t occurred to me before, but it was one of the requirements to serve as a “Social Media Representative” (Neuroblogger, in short) for the Society for Neuroscience, to cover the 2010 Annual Meeting, which I did5

Outreach efforts were also in an embryonic stage at the Society itself at that point, and by picking a few people to cover a giant meeting, one can either give new people a chance to establish a social media presence, boost existing bloggers or do a mix of both. I’m still grateful to the Society for picking me, but predictably some established bloggers were somewhat upset.

In hindsight, I think the choice by the Society to broaden the tent was justifiable as it pushed me and some others to start outreach efforts of any kind. Efforts which I aim to continue into the far future. At the same time, most of the critical blogs are now defunct.

That said, I still don’t think the “neuroblogger” concept itself is particularly well thought out. People attending the meeting will have better things to do than read a blog. People who didn’t go will have their reasons. The neurobloggers themselves will (in my experience) have some tough choices to make between attending the meeting and writing dispatches from it.

What might work better is to have a single “neuroblogger” platform (hosted on the SfN website) where people write contributions from the meeting, squarely aimed at the general public (to satisfy the outreach mission). Basically expert commentary on things that are just over the horizon, but without the breathless and unsubstantiated hype one usually gets from journalists. Perhaps have a trusted, joint twitter account, too.

Anyway. Thanks for giving me my start and I hope to be able to improve on the mission as time goes on. Semper melior.

Posted in Conference, In eigener Sache, Neuroscience | 3 Comments

Did a 6th century Hebrew fortuneteller accidentally do the first documented experiment?

Who did the first experiment? 13th century scholastics like Roger Bacon are usually credited with the invention of the modern scientific method – in particular with regard to doing experiments. Bacon expanded on the work of Robert Grosseteste, who revived the method of induction and deduction from the ancients and applied it to the natural world (going far beyond Aristotle’s intuitive natural philosophy). Others give credit to even later individuals, such as another Bacon – Francis Bacon – who made the experiment the centerpiece of empirical investigations of the natural world.

However, it seems that the first experiment – admittedly with an ad hoc methodology and no clearly spelled out rationale linking outcomes and interpretation, let alone statistical considerations or power calculations – seems to have predated these developments by well over 600 years.

The backdrop to this experiment is straightforward – the Western Roman Empire fell in 476 to an onslaught of Goths, whereas the Eastern Roman Empire soldiered on. A bit more than 50 years later, the Eastern Roman Emperor (Justinian) tasked his General Belisarius to retake the lands of the Western Empire from the Goths, first and foremost the Italian peninsula.

The first experiment?

Experimental design and outcome of what is potentially the first documented experiment.

The history of this conflict is relatively well documented, mostly by contemporary chroniclers like Procopius (in the pay of Justinian, so perhaps not entirely impartial). The story in question might be apocryphal and was already flagged as such by Procopius, but this does not really matter in this case – given that it is mostly the idea (of doing an experiment) itself that is of interest here, not its particular outcome. The story of the experiment is invoked to partially explain why Theodatus – the Gothic king in Rome, characterized by Procopius as “unmanly”, without experience in war and devoted to the pursuit of money – did not come to the aid of the denizens of Naples when they were besieged by Belisarius.

To make a decision whether he should fight Belisarius and try to lift the siege of Naples, Theodatus asked a Hebrew fortuneteller as to the likely outcome of the conflict. The fortuneteller told him to place 3 groups of 10 pigs each (presumably randomly selected) in separate huts, label them as Goths, Italians and East Roman soldiers, then wait a specified (but unstated) number of days. After doing just that, Theodatus and the fortuneteller entered the huts and noted that only 2 pigs labeled as Goths had survived, whereas most of the pigs labeled as East Roman soldiers lived. Of the pigs representing native Italians, half survived but had lost all of their hair. Theodatus interpreted the results to mean that the Italians would lose half of the population and all of their possessions, and that the Goths would be defeated, at little cost to the victorious Eastern Romans. Hence his reluctance to confront Belisarius at Naples.

In any event, Theodatus did not intervene and Belisarius ended up capturing both Naples and Rome from the Goths before being recalled by the Emperor. Losing both of these cities without much of a fight led the Goths to open rebellion and replace Theodatus as king of the Goths. Their chosen successor, Vittigis ordered the fleeing Theodatus to be apprehended and Theodatus perished at the hands of his pursuers.


Here is the original text (from the beginning of book 9, translated):

So the besieged, without the knowledge of the enemy, sent to Theodatus in Rome begging him to come to their help with all speed. But Theodatus was not making the least preparation for war, being by nature unmanly, as has been said before.[36] And they say that something else happened to him, which terrified him exceedingly and reduced him to still greater anxiety. I, for my part, do not credit this report, but even so it shall be told. Theodatus even before this time had been prone to make enquiries of those who professed to foretell the future, and on the present occasion he was at a loss what to do in the situation which confronted him—a state which more than anything else is accustomed to drive men to seek prophecies; so he enquired of one of the Hebrews, who had a great reputation for prophecy, what sort of an outcome the present war would have. The Hebrew commanded him to confine three groups of ten swine each in three huts, and after giving them respectively the names of Goths, Romans, and the soldiers of the [85]emperor, to wait quietly for a certain number of days. And Theodatus did as he was told. And when the appointed day had come, they both went into the huts and looked at the swine; and they found that of those which had been given the name of Goths all save two were dead, whereas all except a few were living of those which had received the name of the emperor’s soldiers; and as for those which had been called Romans, it so happened that, although the hair of all of them had fallen out, yet about half of them survived. When Theodatus beheld this and divined the outcome of the war, a great fear, they say, came upon him, since he knew well that it would certainly be the fate of the Romans to die to half their number and be deprived of their possessions, but that the Goths would be defeated and their race reduced to a few, and that to the emperor would come, with the loss of but a few of his soldiers, the victory in the war. And for this reason, they say, Theodatus felt no impulse to enter into a struggle with Belisarius. As for this story, then, let each one express his views according to the belief or disbelief which he feels regarding it.

Posted in History, Philosophy, Science | 1 Comment

Why “dressgate”* matters

At this point, we have probably all reached “peak dress”, been oversaturated by all matters dress and are ready to move on. But there is more.

There is no question that “the dress” is the most viral image relevant to science in the history of the internet (well more than 9 million tweets in 2 days). Some people noted that this is quite a self-indulgent debate in light of all the serious problems facing the world today. Don’t we all have more important things to worry about? This is a particularly likely sentiment if someone doesn’t immediately “get” what the big deal is about (people are more likely to “get” it, if the interpretation flipped on them as they were looking at the dress, or if someone close to them vigorously insisted that they sincerely see it different).

While it is true that the world faces many pressing problems, discussing the dress is *not* frivolous. Here is why:

1. It’s not about the dress – it’s about visual perception and human cognition.

2. Perception is inherently a guess and even the best guesses can be wrong. It should not be surprising that different people guess differently – or even the same person differently at different times – if the information one starts with is ambiguous.

Two different colors, top vs. bottom, right?

Two different colors, top vs. bottom, right?

3. Basically, the brain is playing a game of telephone. Only the eyes have direct access to the physical light energy in the environment. The human visual system consists of at least 30 distinct areas that get information from earlier ones. All later areas have to rely on what the earlier areas (and ultimately the eyes) tell them is going on. This transmission is fundamentally unreliable. Information is lost at every step.

4. All of this has been documented many times – and known for over 150 years – in many domains of vision, but *not* color vision. To my knowledge, this is the first strongly “bistable” stimulus – where interpretations can be radically different – in the color domain.

How about now? Same colors as above, but with different context

How about now? Same colors as above, but with different context

5. It has been known for a long time that color vision is strongly susceptible to illumination and context. This is not a bug, but a feature that allows to identify objects despite varying illumination conditions. This suggests that the reason people differ in their interpretation is because they differ in their assumption what the light source might be.

The little links between the two regions might convince you that they are actually the same, but look different. Context does matter.

The little links between the two regions might convince you that they are actually the same, but look different. Context does matter.

6. What is particularly intriguing is that the interpretation readily shifts for most bistable stimuli like Rubin’s vase, rotating spheres, etc. – but not for the dress. Some people never shift, others do but on a time scale of hours and once they flip, they can’t flip back. This suggests that there is some kind of rapid perceptual learning going on, much like in “Dalmatian” like situations.

Can you see the dalmatian? If not, see below

Can you see the dalmatian? If not, see below

7. The reasons for this – why different people make different assumptions about the light source and why some people exhibit rapid perceptual learning are fundamentally unknown. There are no shortcuts here. More research on this is needed and will be done.

8. Which is the last point on this list – to my knowledge, this is the first time, a powerful stimulus display has been brought to the attention of science by social media. This also explains why this kind of thing hasn’t happened before. Surely, many people have taken overexposed pictures of fabric (the fabric might matter, too) in poor lighting conditions before. But without social media to amplify the disagreement (social media seems to be best at that), it would have ended there. So what if you disagree with your friend? We all know your friend is a bit crazy and that’s that. Easy to dismiss. But social media changes all that. So we could look forward to more of that.

Can you see the dalmatian now? If you do: Congrats. This can not be unseen. If confronted with a display like the one above, you will always see the dalmatian.

Can you see the dalmatian now? If you do: Congrats. This can not be unseen. If confronted with a display like the one above, you will always see the dalmatian.

To summarize – and repeat – it’s not about the dress. It’s about visual perception and human cognition. If this is the first time you encountered that your perception – that you rely on to get safely through the day – is inherently and fundamentally unreliable, you might be skeptical, defensive or shocked. But that doesn’t change the facts.

So yes, ISIS is an obvious concern. But that doesn’t mean “the dress” is trivial. It is not. As a matter of fact, I would argue that this could not be more topical. If we can’t agree about the color of a dress, how can we hope for world peace? How can we foster tolerance if we don’t allow for and don’t understand that other people can sincerely see the world differently from us?

To be perfectly clear: The question is not what the color of the dress actually is. The question is why people disagree so strongly.

What follows from this is that finding the original dress is not a solution to the issue. Neither will any clever analysis of light distributions in the image. There are no shortcuts here. In other to find out why the interpretation has flipped on you or why your interpretation disagrees with that of someone you care about, more research is needed. At this point, the answer is: “We don’t know, but would like to find out”. Dismissing things is easy. Research is hard.

Note: We understand a lot about how vision works and how it doesn’t render a veridical percept of objective reality. But that is not the point. Vision mostly just has to be useful for survival purposes. But that does not account for the fact that different people see the same image of the dress (on the same screen) differently. It is important to acknowledge our ignorance in this regard and plan to do some research to overcome it.

Human perception is more variable than most people realize, both within the same person over time and between people. This goes beyond perception, by the way. Lots of people say things like: “You said x” or “this is offensive” – a more accurate statement would be “I understood x”, or “this is offensive to me”. Big difference. So it is always advisable to keep an open mind.


*Not my creation. This was one of the trending Twitter hashtags.

Images shared with kind permission from Steve Shevell.

Posted in Neuroscience, Psychology, Science, Social commentary | 9 Comments

Lessons from the dress: The fundamental ambiguity of visual perception

The brain lives in a bony shell. The completely light-tight nature of the skull renders this home a place of complete darkness. So the brain relies on the eyes to supply an image of the outside world, but there are many processing steps between the translation of light energy into electrical impulses that happens in the eye and the neural activity that corresponds to a conscious percept of the outside world. In other words, the brain is playing a game of telephone and – contrary to popular belief – our perception corresponds to the brains best guess of what is going on in the outside world, not necessarily to the way things actually are. This has been recognized for at least 150 years, since the time of Hermann von Helmholtz. As there are many parts of the brain that contribute to any given perception, it should not be surprising that different people can reconstruct the outside world in different ways. This is true for many perceptual qualities, including form

Rubin's vase: A classical example of figure/ground segmentation. The image is fundamentally ambiguous. People perceive a vase or faces, but not both at the same time.

Rubin’s vase: A classical example of figure/ground segmentation. The image is fundamentally ambiguous. People perceive a vase or faces, but not both at the same time.

and motion. While this guessing game is going on all the time, it is possible to generate impoverished stimulus displays that are consistent with different mutually exclusive interpretations, so in practice the brain will not commit to one interpretation, but switch back and forth. These are known as ambiguous or bistable stimuli, and they illustrate the point that the brain is ultimately only guessing when perceiving the world. It usually just has more information to go by and disambiguate the interpretation.

A bistable motion stimulus. Do you see the dots moving from left to right or up and down?

A bistable motion stimulus. Do you see the dots moving from left to right or up and down?

This is also true for color vision. The fundamental challenge in the perception of color is to identify an object despite changing illumination conditions. The mixture of wavelengths that reaches our eye will be interpreted by the brain as color, but which part is due to the reflectance of the object and which part is due to the illumination?

This is a inherently ambiguous situation, so the brain has to make a decision whether to take the appearance of an object at face value or whether it should try to discount the part of the information that stems from the illumination. As the organism is not primarily interested in the correct representation of hues, but rather the identification of objects in light of dramatically varying conditions (e.g. a predominance of long wavelengths in the early morning and late afternoon vs. more short wavelengths at noon), it is commonly accepted that the brain strives for “color constancy” and is doing a pretty good job at that.   But in this tradeoff towards discounting, something has to give, and that is that we are bad at estimating the apparent absolute hue of objects. For instance, a white surface illuminated by red light will objectively look reddish. The same white surface illuminated by blue light will objectively look blueish. In order to recognize both as the same white surface, the subjective percept needs to discount the color of the light source.

So it should not be surprising that inference of hue can be dramatically influenced by context. The same shade of grey can look almost black on a bright background but almost white on a dark one.

Lightness illusions are common. The shade of grey above and below the horizon are the same. You can see this by covering the strip in the middle

Lightness illusions are common. The shade of grey above and below the horizon are the same. You can see this by covering the strip in the middle

Note that this is not a bug. It is a necessary tradeoff in the quest to achieve a stable appearance of the same object, regardless of context or illumination.

So far, so good. Now where does the dress come in? The latest sensation to sweep social media has sharply divided observers. Some see the dress as gold on white, others as black on blue.

White/gold vs. Black/blue: Some people perceive the image on the left, others the one on the right. Others switch back and forth.

White/gold vs. Black/blue: Some people perceive the image on the left, others the one on the right. Others switch back and forth.

As noted before, this kind of divergence of interpretation might be rather common with complex stimuli. The importance of the “dress” stimulus is the extent to which intersubjective interpretation differs in the color domain. To my knowledge, this is by far the most extreme such stimulus. Of course one has to allow for the fact that not everyone’s monitor will be calibrated in the same way and viewing angles might differ, but this doesn’t account for the different subjective experience of people viewing the exact same image on the same monitor from the same position. And of course the reason why the “true colors” of the dress are in dispute in the first place is the color constancy phenomenon we alluded to above. This was likely a black/blue dress that was photographed with poor white balance, giving it an ambiguous appearance. But that doesn’t change the fact that some people sincerely perceive it as white/gold.

That the interpretation of the color values itself depends on context can readily be seen if the context is taken away. In the image below, some stripes were extracted from the original image without altering it in any other way. The “white/blue” stripe can now be identified as light blue and the “gold/black” stripe as brown.

Stripes, out of context: One now unambiguously looks like blue, the other like brown.

Stripes, out of context: One now unambiguously looks like blue, the other like brown.

But why the difference in interpretation? That is where things get interesting. If the ambiguity derives from color constancy (and it looks like it does), the most plausible explanation is that people differ in their interpretation of what the illumination source is. Those who interpret the dress as illuminated by a blue light will discount for this and see it as white/gold whereas those who interpret the illumination as reddish will tend to see it as black/blue. Interestingly, the image itself does allow for both interpretations, the illumination looks blueish in the top of the image, but yellowish/reddish in the bottom. On a more fundamental level, a blue/black dress illuminated by a white light source might be indistinguishable from a white/gold one, but with a blueish shadow falling onto it.

But if this is the case, one should be able to consciously override this interpretation once it is pointed out, but – for most people – this does not seem to be the case, in contrast to most other such ambiguous duckrabbit displays. People are able to willfully control what they see.

Inherently ambiguous stimuli. Interpretations switch, they don't blend. But people can consciously override interpretations once they are pointed out.

Inherently ambiguous stimuli. Interpretations switch, they don’t blend. But people can consciously override interpretations once they are pointed out.

This raises several intriguing possibilities. For instance, it has been recognized for quite a while that the human “retinal mosaic” – the distribution of short-, medium- and long-wavelength cones in humans is radically different between observers, but this seems to only have a minute impact on the actual perception of color. Perhaps it is the case that differences in retinal mosaic can account for difference in the perception of this kind of “dress” stimulus. Moreover, there is another type of context to consider and that is temporal context. We don’t just perceive visual stimuli naively, but we perceive them in the context of what we have encountered before – not all stimuli are equally likely. This is known as a “prior”. It is quite conceivable that some people (e.g. larks, owls) have a different prior as to what kind of illumination conditions they encounter more frequently. Or a complex interaction between the two.

While we must confess that we currently do not know why some people consistently see the dress one way, others consistently in another way and some switch, it is remarkable that the switching happens on very long timescales. Usually, switching is fast, for instance in the Rubin’s vase stimulus above. This could be particular to color vision. There are no shortcuts other than to do research as to the underlying reason that accounts for this striking difference in subjective perception.

Meanwhile, one lesson that we can take from all of this is that it is wise to assume a position of epistemic humility. Just because we see something in a certain way doesn’t mean that everyone else will see it in the same way. Moreover, it doesn’t mean that our percept necessarily corresponds to anything in the real world. A situation like this calls for the hedging of one’s bets, and that means to keep an open mind.  Something to remember next time you disagree with someone.

Who is right? Does the question even make sense? Or is it important to see the bigger picture?

Who is right? Does the question even make sense? Or is it important to see the bigger picture?


Posted in Neuroscience, Psychology, Science | 4 Comments