Header 1

Our future, our universe, and other weighty topics

Saturday, January 28, 2017

Neural Correlation Studies Often Lie With Colors

A very interesting question is whether there are particular parts of the brain that are strongly associated with particular facets of human mental functionality. Are there, for example, regions of the brain that work much harder when you learn something, or remember something, or feel something? The idea that there are such areas is a hypothesis called localization.

Some claim that this idea of localization is supported by brain imaging studies. It is claimed that quite a few studies tell us about the neural correlates of conscious experiences. In a typical study of this type, people will have their brains scanned by some instrument such as an MRI machine. Then scientists will look for certain parts of the brain which showed more activity (such as blood flow) when some particular type of mental activity was occurring.

But there are reasons for thinking that such studies tell us very little. For one thing, brain imaging studies on the neural correlates of consciousness typically involve only small numbers of participants (often fewer than 25). Making generalizations from such small samples is dubious.

Also, claims that particular regions of the brain show larger activity during certain mental activities are typically not well-replicated in followup studies. A book by a cognitive scientist states this (page 174-175):

The empirical literature on brain correlates of emotion is wildly inconsistent, with every part of the brain showing some activity correlated with some aspect of emotional behavior. Those experiments that do report a few limited areas are usually in conflict with each other....There is little consensus about what is the actual role of a particular region. It is likely that the entire brain operates in a coordinated fashion, complexly interconnected, so that much of the research on individual components is misleading and inconclusive.

There have been statistical critiques of brain imaging studies. One critique found a common statistical error that “inflates correlations.” The paper stated, “The underlying problems described here appear to be common in fMRI research of many kinds—not just in studies of emotion, personality, and social cognition.”

Another critique of neuroimaging found a “double dipping” statistical error that was very common. New Scientist reported a software problem, saying “Thousands of fMRI brain studies in doubt due to software flaws.”

Considering the question of “How Much of the Neuroimaging Literature Should We Discard?” a PhD and lab director states, “Personally I’d say I don’t really believe about 95% of what gets published...I think claims of 'selective' activation are almost without exception completely baseless ”

Another huge reason for being skeptical about brain imaging studies is that such studies very often use very misleading visual presentations, creating false impressions. What very frequently goes on is something like this. A series of brain scans will show a very small difference between brain activity in different parts of the brain – typically only 1%. A Stanford scientific paper on fMRI uses this 1% figure, making an exception only for small parts of the brain (“visual and auditory cortices”) associated with seeing and hearing. The paper makes this generalization: “While cognitive effects give signal changes on the order of 1% (and larger in the visual and auditory cortices), signal variations of over 10% may arise from motion and other artifacts in the data.” In other words, people moving their heads (and other misleading signals) may create the impression that there is a higher variation in the non-sensory parts of the brain, but the real variation in the signal changes is only something like 1%. A similar generalization is made in this scientific discussion, where we are told the following:

For example, most cognitive experiments should show maximal contrasts of about 1% (except in visual cortex),  hence, if estimates for a single subject are much larger than that, then the estimates are likely to be bad. Poor estimates can arise from head motion, or sporadic breathing patterns by the subject, or sometimes from a poor design matrix that is ill-conditioned.

But again and again studies on neural correlations will produce a visual which grossly exaggerates this very small difference of 1%, making it look like a great big difference. This is lying with colors
To explain why this is highly deceptive, let's consider some examples of displaying visual information: an honest presentation and a misleading presentation. Imagine you have a home for sale, and you are preparing a web page or brochure that describes your house's selling points. One of the key factors in selling houses is the quality of the local school district. Anyone with children will want to buy a house in a neighborhood with better schools.

Imagine you've got the average school stores for your home's school district, and the data looks like this:

District Average Reading Score
District 1 80
District 2 80
District 3 80
District 4 (yours) 81
District 5 80
District 6 80
District 7 80
District 8 80

Now imagine you wanted to present a school district map highlighting the higher score of your home's school district. For you to honestly present such information, you would have to follow this rule: the difference in the color shade should be no different than the differences in the data that you have.

So if you were to present an honest school district map, color-coded school scores, it would have to look something like this:

This would be an honest map. It honestly indicates only a very slight difference between the school scores in your home's school district and the nearby districts. But you might be tempted to present the data differently. You might present it like the map below.

This map would be better from the standpoint of selling your house, since it would leave someone with the impression that your house's school district has much higher scores than the nearby districts. But given the actual data showing only a 1% difference, it would be utterly misleading to present a map like this. The map would incorrectly give someone the idea that your home's school district had scores maybe 30% better than surrounding districts. Presenting a map like this would be an example of lying with colors.

It is exactly such lying with colors that goes on again and again in brain imaging studies on the neural correlates of consciousness. Again and again, such studies will show visuals that depict differences of only 1% or less between blood flow in different regions of the brain. But such regions will be shown as red regions in brain images, with all of the other areas having a grayish “black and white” color. When you see such an image, you inevitably get the impression that the highlighted part of the brain has much higher activity than other regions. But such a conclusion is not what the data is showing.

So, for example, a study finding 1% higher brain activity in a region near the corpus callosum (under some activity that we may call Activity X) might release a very misleading image looking like the image below, in which the area of 1% greater activity is colored in red.

But such an image is lying with colors. If there is only a 1% greater activity in this region, an honest diagram would look like the one below.

With this diagram, the same region shown in red in the first diagram is shown as only 1% darker. You can't actually tell by looking at the diagram which region has the 1% greater activity when Activity X occurs. But that's no problem. The diagram above leaves the reader with the correct story: none of the brain regions differ in activity by more than 1% when Activity X occurs. Contrast this with the first image, which creates the very misleading idea that one part of the brain is much more active than the others when Activity X occurs.

You might complain that with such a visual, you cannot tell which regions have the slightly greater activity. But there are various ways to highlight particular regions of a brain visual, such as circling, pointing arrows, outlining, and so forth. For example, the following shows a region of high activity without misleading the viewer by creating the impression of much higher activity:

The misleading diagrams of brain imaging studies seem all the more appalling when you consider that the images in such studies are typically the only thing that laymen use to form an opinion about localization in the brain. The text of brain imaging studies is typically written in thick jargon that only a neuroscientist can understand. Frustrated by this very hard-to-understand jargon and unclear writing, every layman reading these studies forms his opinions based on the visuals. When such visuals deceive us by lying with colors (as they so often do), the whole study ends up being something that has the effect of creating misleading ideas.

At 4:47 in this online course, we are told that the blood changes in the brain are quite small when observed with an MRI, between 0.1% and 5% (based on two previous comments I quoted, the higher value seems to be only found in the auditory cortex or the visual cortex). The speaker in this course tells us that if we were to just watch a movie of the fMRI scans, we wouldn't be able to notice the changes between different brain regions. But the visuals in neural correlation studies misrepresent this minimal change, making it look like a great big change. These cases of lying with colors give readers a very misleading impression that brain activity involving thinking and memory recall is very localized, and tightly correlated with mental activity.

How closely your brain is correlated with your mind is important from a philosophical standpoint. If different parts of our brains surge dramatically with blood when we think or recall memories, that is a point favoring the idea that your mind is just a product of your brain. But if different parts of your brain look pretty much the same when you think or recall memories, that's a point in favor of the idea that your mind and memories may involve something much more than your brain, perhaps some soul or some higher cosmic consciousness infrastructure. The actual data from brain imaging is the second of these cases: different parts of the brain show about the same activity when thinking or memory recall occurs. But by doing neural correlation studies that visually make tiny changes look like huge changes, our neuroscientists almost seem to be trying to fool us into thinking that a very different thing is going on, that particular parts of our brain light up dramatically when our higher mental functions are engaged. To such neuroscientists we should say: visually represent your own data honestly, and stop lying with colors.

No comments:

Post a Comment