Mind: The Brains Behind the Eyes

 

I suffer a disability of cognition. I cannot remember directions. In past when I commuted in city buses, I spent many frustrating moments on a road trying to figure out the direction of the place I was heading to. Bus number 72 plied in both the directions. I would often board the wrong bus and learn the error only when the bus halted at its last stop. Today, if a traffic jam or any obstacle forces me to take a new route, I cannot reach home without getting lost in the maze of crisscrossing streets. Recently, on a foggy winter day, I was forced on to an unfamiliar street as I pulled my cycle with a  punctured tyre. The new route might be shorter, I reasoned. A right turn here and a left there and I was lost. I spotted a lonely walker and stopped him to ask the way to my apartment. He seemed dazed and stared hard at me for a few seconds, as if I had asked him the solution to the Fermat’s Last Theorem. He repeated the name of my apartment building slowly. Had he heard me correctly? I nodded. ‘Just across the road,’ he blurted and rapidly walked away. I looked intently and saw the gate I enter every day – but from a different direction.

I understood my disability a little when I read the fascinating story of vision as told by science.

 

Vision is the cardinal sense. Eye, the primary source of vision, is incredibly complex. William Paley, an eighteenth century English theologist, employed the intricate design of human eye to bolster his argument for a God who had created living organisms. A man, postulated Paley, accidentally stumbles on a watch in his walk and the watch comes apart. Bemused, man observes the various parts of the watch working in tandem toward a common goal. When he thinks how this watch came into existence, image of a watchmaker conjures in his mind, who must have designed this marvellous machine. According to Paley, it is inconceivable that human eye vastly more elaborate than a watch, could have been crafted without the agency of a creator.

Charles Darwin, who single-handedly shattered the millennia old myth of a creator, confessed that at first sight origin of eye seems contrary to the theory of the origin of species by natural selection. ‘To suppose that the eye, with all its inimitable contrivances…could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.’  In his epoch-changing book, The Origin of Species, he went on to explain how nature might have accomplished this seemingly impossible task. Richard Dawkins, an evolutionary biologist and an indefatigable champion of Darwinism, in his book Climbing Mount Improbable describes clearly how the crude but useful gradations of eyes evolved into the stunning design of the complex camera-eye of the animals today.

Notwithstanding the arguments over its provenance, in the sublime crannies of a divine mind or in the mindless chugging of mundane laws of nature, vision transformed life on earth. The bumbling, aimlessly wandering organism could now easily locate the source of its food, avoid a predator, search for the prey, know the neighbour as an enemy or a friend, and look for shelter. Life without vision is unimaginable.

Seeing is ubiquitous in our language, asserting the primacy of this sense. We not only see the objects in an external world, but see within ourselves and into other human beings. We see a point of view in an argument. We see the beauty in a piece of music. We see the working of the physical world and of our minds. We see into a past and into the future.

Vision is the most instructive of our senses that help us to perceive the world. Blind process of evolution hit upon a novel source for gathering information about the physical world in the form of vision. Energy of the Sun, responsible for the cellular processes that ensure life, is harnessed to make the organism aware of the world around it. Photons bouncing from the objects, near or far, hot or cold, big or small, smooth or rough, stationary or moving, inanimate or alive, converge on a light sensitive screen in the eye – The Retina. Minor electrical fluctuations in the nerves emanating from retina are fed into the brain. Brain, like a magician, invokes for us a world through these nerve signals; a world replete with colour, a world of enchanting play of light and darkness, a world of stupefying stillness and scintillating movements.

Vision is as old as life. First light sensitive organisms were the Cyanobacterium that originated about two – perhaps more than three – billion years back. They used photons to synthesize energy. Few organisms like jelly fish, can vaguely sense the presence of light, i.e., just distinguish day from night. Journey from this crude light sensitive surface to the sophistication of a vertebrate eye is many hundred-million years long. And the product is an apparatus that can focus the haphazard rain of photons on to its light sensitive screen in the eye and a mind that can process these signals to make sense of a world. Advantages this apparatus conferred on its owner are so momentous that a strictly parsimonious nature stumbled on vision on forty, possibly sixty, occasions, during the process of evolution, bestowing on its creation that many ways of seeing.

We believe that our vision produces for us a precise image of the world as it is. A brief survey of various visual illusions can bust this myth. Parallel lines converging in distance, congruent lines looking unequal, Kanizsa triangle seen which is actually not there, Rubin face-vase flipping between a goblet and a pair of profiles tete-a-tete, a figure that is a rabbit and a duck too. We know instinctively the truth of the statements: seeing is believing, I saw it with my own eyes, I have the testimony of an eye witness. Then what is happening? How can an infallible sensory organ be flummoxed so easily?

Unequal yellow lines?

Triangle seen, but no trace in the figure

Vase or profiles?

Rabbit or duck?

But vision did not evolve to enable us to appreciate the world in its true glory: serene grace of a rising sun, high mountains half-drowned in clouds, or the bewitching beauty of the painted ceiling of Sistine chapel. Its sole purpose was to offer its owner an edge in overall survival and reproduction in their environment.

 

Mind does not store images of all the possible objects in its memory, against which it matches the image in the eye and interprets a true picture of the world. Instead, mind analyses an image on presumptions it learned in its millions of years of evolution and which are now ingrained in its structure. It evolved in a world where matter was cohesive, surfaces were uniformly coloured, objects did not scatter to intentionally take up confusing positions. It uses these propositions to deduce for us a world where we can recognise our partner, pluck the fruit from a tree, do not bump into the wall ahead, can avoid a vehicle in our path, dodge a stone thrown at us, do not walk over the edge of a cliff.  When the visual field is mischievously altered by a smart psychologist or by a chain of spooky coincidences, mind is confused. When the world resembles the environment, in which it evolved, mind shows us the world where we can make a living, i.e., survive to procreate.

Objects in the world are immensely varied in size, colour, shape, depth, distance, shading, consistency, and degree of motion. Mind has very few clues to discern these attributes from the inverted, two-dimensional image formed on retina. Optical illusions are the proverbial exceptions that prove the rules of visual perception and thus provide us a window through which we can peep into the workshop of this fabulous contraption of nature – The human mind.

Depth perception of objects in a field of vision is intensely perplexing. A photon reflected by an object and captured by the retina, could retrace its path to infinity. Retina has no way of knowing which object in this endless path bounced the photon. But mind does not search all infinity to know the position of the object. It zeroes on to the position instantly. Mind uses some assumptions to ascertain depth. Distant objects appear smaller. Parallel lines converge in distance. A gradual change in texture and colour of surfaces is caused by perspective. A bit of object ‘A’ bitten off by the object ‘B’, implies ‘A’ is behind ‘B’. In a moving picture, objects that are further move at a slower speed than the ones nearer. Painters utilise these rules of perspective to realistically capture the landscape on a canvas. A scene painted well conveys the sense of depth. But mind effortlessly knows it to be a painting and not the reality.

Stereograms, the three-dimensional (3D) pictures, offer a clue to the mechanism of 3D vision. Though an intuitive belief, nature did not evolve two eyes to maintain symmetrical layout of the body or as a back-up for an essential sensory organ. Eyes are situated about two and a half inches apart in the skull. Image of an object projected on two retinae do not occupy symmetrical location in each globe. Nearer objects form images that are further apart on two retinae, i.e., nearer the temples. Images projected by farther objects are nearer to each other, i.e., crowded in the nasal halves of the retinae. A simple rule of trigonometry can tell one the distance of the object from the eyes. Brain with its trillions of synapsing neurons does these calculations unconsciously, instantly, and continuously as one gazes at the world. This is the stereoscopic vision, stereo in short. Brain merges the two images of the object generated in each eye into a composite 3D image – the Cyclopean image.

Binocular Vision and Depth Perception

Stereograms utilise the principles of stereo vision to generate 3D image from a 2D source. Each eye is fed the image meant only for it. This is achieved by using different coloured images for each eye, e.g., red for left and green for right. Viewer wears different coloured glasses for the two eyes. Image of each eye can also be split by using differently polarised lights or by liquid-crystal displays. is fooled into believing that two different images are being generated by the same object and fuses them to produce one 3D image. Stereograms require use of some viewing apparatus. Autostereograms are viewed by a naked eye. They use repeated pattern of multiple images to create the illusion of 3D perspective.

Autostereogram

Mind is a terrific computer. It could have stored the model of all the objects in the world, within itself. But graphics need tremendous space. Even mind’s hardware, the brain with its hundred billion neurons and more than hundred trillion synapses, would be grossly inadequate for this task. Nature hit upon an ingenious solution in vision. It lets the world store all the information about the objects in it. Mind is equipped with a capability to read this information utilising principles of optics and trigonometry – laws that were discovered by us millions of years after nature incorporated these in the vision apparatus.

Shape recognition is another intriguing property of mind. Mind is capable of recognising millions of shapes. These are not discreetly labelled and stored in brain. It is now believed that brain has about twenty to forty basic shapes- known as geons – stored in the shape-recognition area. Description of millions of objects can be generated by combination of these geons in various ways: one upon another, end to end, end to middle, larger than next, etc. Geons are like words of a language. Rules of syntax of the language are hardwired in human brain. Combination of words according to these rules generates infinite sentences – a unique attribute of language.

Some geons (left) and their combinatorial power to describe shape

Face recognition, a singular facility of mind works differently from shape perception. A collection of neurons in the temporal lobe of brain, the fusiform face area, is dedicated for this. But like shapes, brain does not store all the features of the thousands of faces a person can recognise. Only the salient traits of a face that distinguish it from others are stored. When these are noted in a face, mind instantly recognises it. Cartoonists have exploited this trait in drawing caricatures of famous people: the long nose of Indira Gandhi, prominent pout of Narsimhan Rao, the cherubic face of Rajiv Gandhi, the spherical body and face of Jayalalitha.

Face recognition

Eyes merely form an image of the object on retina. This image is not vision. Vision is the description of this image. Brain achieves this. Five rectangles standing upright on a flat rectangle, announces the eye. Five books stacked on the bookshelf; brain interprets. Eyes notice a squiggle of small scribblings. Mind reads the fascinating story being told by these words. Eyes view a tall figure approaching you with open arms at the airport. Mind recognises a beaming friend you are seeing after many years.

Mind sees what eyes look at. To look is defined as turning one’s eyes towards any object, i.e., a physical movement. To See is to perceive something. Perception is the process of recognition or relating. Mind is as vital to vision as are eyes. Dysfunction of the visual neurons in brain lead to a peculiar form of blindness known as visual agnosia. Agnosia is the loss or diminution of the ability to recognise familiar objects or stimuli. In visual agnosia, victim can see the shapes of the objects, but cannot decipher what they stand for.

Oliver Sacks, a neurophysician and a popular writer of books on strange afflictions of mind, presents stories of some of his patients who suffered various forms of visual agnosia, in his absorbing book, The Mind’s Eye. Lilian, a professional pianist, came to Sacks because she realised in the middle of a concert that she couldn’t read the score, although she saw the individual notes quite clearly. She suffered from posterior cortical atrophy, a degenerative disease of the neurons in visual area of brain. Patricia became aphasic after a stroke. She could recognise people but could not understand their speech nor speak her mind. But she was a doughty, lively woman ‘who had a passion to communicate…and talked twenty-four hours a day’. In a few years she learned to accurately read peoples’ faces as they spoke to her and could communicate through gestures. She again led a vibrant social life from her wheel chair. Such compensation for a lost ability, by an extraordinary growth and development of a contiguous brain area, is known in neurosciences. Howard Engel, a Canadian writer, suddenly discovered one morning that he could not read the headlines in the newspaper lying on the floor. He learned that he could still write easily, but could not read what he had written. Charles Scribner, Jr., also a man of letters, owner of a publishing house, developed similar affliction when he was sixty. This is one form of visual agnosia, alexia. Scribner compensated for his disability by switching to audiobooks and dictation. Howard couldn’t give up reading which was his life. He painstakingly and very gradually learned to read slowly by vocalising words as he read, rolling them repeatedly if they failed to make sense, till he learned their meaning. Oliver Sacks also wrote in the book about his lifelong difficulty in recognising faces, a disorder known as prosopagnosia. Prosopagnosics can recognise the person by their voice, gait, or gestures. But faces leave them bewildered. He also talked about his other affliction, topographical agnosia – agnosia for salient topographical features such as streets, houses, roads. Hence, also known as landmark agnosia. And I discovered the name of my disability.

 

Field of vision is large. I have focussed my attention on a very limited area. For the rest, I've been content to merely articulate my overawed admiration of nature's fathomless power of creation, eschewing any explanation of the mechanisms involved. Writeup is bursting at its seams, and fear of adding to verbosity - that may offend a stray reader of this blog - dissuades me from going any further. I read about vision in many books. I have mentioned a few. Steven Pinker’s How Mind Works, has an excellent essay on vision. It is demanding, but understanding as it dawns, leaves you spellbound.

Mapping of the mechanism of vision, through investigation of the specific visual defects in various brain disorders and through analysis of optical illusions, is a supreme example of the rigour and triumph of science. It also illustrates how simple laws of nature, in their millions of years of slow, relentless grind, have given rise to stunningly complex and marvellously endowed living machines. To attribute these to the design of an imaginary omnipotent being is nothing but extreme intellectual sloth.

‘There is grandeur in this view of life…whilst this planet has gone cycling on…from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.’ Wrote Darwin, lyrically and movingly, in the last paragraph of The Origin of Species. Science enhances this sense of wonder in the beauty of nature while mythological beliefs in divine creation threaten to dull the euphoria of this discovery.