Visual perception is not just making a replica, says neuroscientist Vilayanur S. Ramachandran

 thehindu.com  05/23/2020 12:21:43 

Vilayanur S. Ramachandran, neuroscientist, has made path-breaking advances in the study of the human brain. During the lockdown, this writer got to talk [on Skype] with Prof. Ramachandran, Director of the Centre for Brain and Cognition, University of California, San Diego, and Professor of Biology at the Salk Institute, about how he studies and analyses his patients. Here is his analysis of an astonishing case study  of a patient who saw everything upside down.

He describes the logic behind the method he adopts in investigating even the oddest symptoms that some patients manifest: First, is he really experiencing the symptoms or making it up  for insurance claims? Second, if real, whats causing it in the brain? Third, in addition to explaining his curious symptoms, what can it tell us about normal brain function and what are its broader implications? Fourth, can you cure the patient?

The human brain is normally programmed  either by genes or by feedback  to see things the correct side up. If I showed you a book with a familiar picture, of, say, Mahatma Gandhi or Jawaharlal Nehru, and it was upside down, you would not recognise it. You would only recognise the person if it were the right side up. That is the way your brain is wired, he explains.

Visual perception

Visual perception is not just making a replica. Prof. Ramachandran explains: You learn in school that your eye is like a camera lens and that it inverts the image and your brain sets it right by inverting it again. But this is wrong, because there is no picture in the brain. We accepted the explanation in school but its wrong, unless the teacher were being metaphorical.

Studying perceptual and cognitive deficits opens the way to understanding consciousness, emotions, seeing, recognising, everything, he adds, warming up to the topic on hand  the patient who was saying that he was seeing things upside down.

We showed him a matrix of faces in a computer screen, most of them were right side up and one was upside down. In normal people the brain is immediately able to discover the upside-down image. But if only one is right side up and all the rest are upside down, the brain is unable to identify which is the right-side up face. We found that unlike normal people, he was better at discriminating inverted faces than upright faces. I suspect that this may be because his face recognition centre buried in the temporal lobes is only partially damaged. When the wave of neural activity first arrives, it cannot avoid triggering the partial activation and partial engagement of the face-recognition module  but given the damage in the module, it fails completely. If an upside down face is viewed, the triggering doesnt occur so you are allowed to switch strategies and try using other tricks  like point-by-point comparison of features to determine the extent of similarity, he elaborates.

He goes on to describe an experimental scheme called Johanssons point light walker. It is a minimal drawing consisting of bright points, and when the light points move in synchronicity, the brain constructs a human walker from it. If we turn the point-light walker image upside down, the brain does not complete the image to make out a person from the points. But with this patient who claims to see things upside down, its just the other way around. He cannot see the walker when they are right side up but sees them when the screen is place upside down.

Now why does this happen, and what is wrong with the brain?

Early image

As Prof. Ramachandran says, very early, during image processing, in the retina, the brain maintains some image characteristic. Then the signal branches into many sets. One set goes to the parietal lobes (side areas) of the brain, others to the temporal lobes (slightly below), the occipital lobes, and so on.

The main two branches are the ones that go to the temporal and parietal lobes. I call the top branch the how stream or how pathway and the bottom one the what pathway, he says, proceeding to outline the process of visual perception. If the how pathway is damaged, in a bilateral stroke, for instance, then the patient can still recognise objects. But if you ask him to grab it, he reaches out in a different direction, unable to grab the object even though he can recognise it. After extensive treatment he can acquire the ability to do this correctly. On the other hand, if the what pathway is damaged, the converse happens.

Another possibility is that that both the ventral and dorsal (parietal lobe, how pathway) streams were affected equally. But then he started recovering his dorsal stream functions by re-learning it. Like, he reaches out his hand to pick up something and when it is wrong he re-learns the whole thing. After being crude and slow at first, after the re-learning process, he is able to point and place his hand correctly, says Prof. Ramachandran. For the ventral stream, however, such a learning process cannot happen because there is no feedback. For instance, when trying to identify different faces, he does not get any immediate internal feedback, so he cannot re-learn them.

Now, this gives a good explanation but there is still one problem. Why is he seeing things upside down? If the pathway is damaged, he should see things randomly, so why is he seeing them upside down?

Primitive mechanism

He himself answers the question: The only thing I can think of is that there is a primitive (evolutionarily ancient mechanism), default mechanism in the brain which allows something like rotation or inversion to occur before further processing, and his brain has partially reverted to that mode. He adds, quickly, But thats not really an explanation. As for a cure, that is still some distance away. We need to do some brain imaging  not a fishing expedition as it often is, but to rule out or confirm our ideas, he concludes.

Research matters

In an answer to a query on what matters in research, he recalls how Francis Crick would always advise people to look at the big problems.

When you are doing research, there is also a tendency to get trapped in cul de sacs of knowledge. You referee each others papers and pat each other on the back. It sounds cynical, but a lot of science is done that way. You should not become part of a club, you should do your own thing, he says. On the other hand he is also a firm believer in the idea that nature is not conspiring to make important problems difficult. DNA [structure] was a very important problem but it turned out to be quite easy actually to solve, once Jim Watson, Francis. Crick and Rosalind. Franklin put their minds to it. he declares, smiling.

Crick was a formidable presence here during the two decades when we were colleagues at the UCSD, and an inspiration to all of us, but many others were also informal mentors  my brother, Ravi, whose idealistic and romantic world view rubbed off on me, and O.L. Braddick, Colin Blakemore and, especially, Richard Gregory and John Pettigrew.

Prof. Ramachandrans stance is this: If you have some new observation that will not fit the current picture of science, which threatens to upset this huge cathedral people have built  Copernican, Newtonian, Einsteinian and Heisenbergian, or even smaller edifices  you must then not hesitate to tear it down and start from the scratch. Young scientists should aim for such a revolution. You dont want to be a bricklayer but a revolutionary.

Revolutionary science

How does one cause a revolution in science? The first step is in smelling out an anomaly.

First, if you have an anomaly, you have to see if its genuine or not. An anomaly is like the smell of burning rubber  you get the sense that something is not okay, he says, giving the example of the discovery of the theory of continental drift. He says, A child can see that the west coast of Africa fits the east coast of South America like a bit of a jigsaw puzzle. Till mid-twentieth century, people were saying it is a coincidence. Until one person came along and said it was more than that. Then came finding fossils on the two coastlines, for example, a 250-million-year-old freshwater lizard called the Mesosaurus. He elaborates, There are also freshwater snail fossils. How did they get there? You find sauropod bones on the west coast of Africa, the same ones you find on the other side also. But still no one can imagine terra firma drifting. Later, this was explained using the theory of continental drift. The evidence was staring at them in the face, no one disputed the facts but it was all a matter of interpretation, he says.

Dont give up a theory, however absurd it may seem, because you cant think of a mechanism or because it doesnt fit in with the big picture. The mechanism may not have been found yet. In fact, it may lead you to find a new mechanism which hasnt been thought of so far, he advises.

Bacterial transformation experiment

To illustrate this, he describes how a British group had an experiment in which they showed bacterial transformation. In the lab, with two types (A, smooth and virulent, and B, rough and non-virulent strains) of the bacterium Streptococcus pneumoniae, they saw Strain B developing a smooth capsule like Strain A and becoming virulent. [Not knowing the mechanism at work, they concluded Strain B was turning into Strain A.] It was published in an important journal, but hardly anyone paid attention to this. It was a important result, but because it was just bacteria, no one paid attention. Then along comes [Oswald T.] Avery. He showed that you dont even need to incubate them together. He just took the juice [extract] from one species and incubated the other strain with the same, and he showed that the species would transform, laying the foundation of molecular genetics.

Prof. Ramachandran describes how [Erwin] Schrodinger asks what this chemical is (Schrodinger wrote about this in his influential book What is life?)  it is the DNA. In the book, He [Schrodinger] asks what is the other evidence that it is indeed the DNA that is the genetic material. But Avery had stumbled upon this years ago with the experiment on bacteria. Now why did people ignore Avery? Because they couldnt think of a mechanism. So my argument is  dont throw away something just because you cannot think of a mechanism, he concludes.

The other criterion for carrying out research is that of simplicity and elegance, he says.

There is an aesthetic dimension to science. It seems not to hold true these days, as we become more part of the corporate world. We are tainted with & utility, Prof. Ramachandran adds, almost as an afterthought.

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