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The Blind Spot and the Giant Hand

The blind spot is a well-known psychological phenomenon that is a direct correlate of an anatomical structure in the eye. The eye communicates with the brain by virtue of the fact that specific neurons in the eye project their axons out of the eye to the brain. Where this bundle of axons exits the eye is called the optic nerve head, and it turns out that the axons themselves actually crowd out the light sensors of eye, the photoreceptors, so that the light that falls onto the optic nerve head during formation of an image is lost. We are literally blind to this spot in the visual world. Unless you are specifically looking for it you don’t even notice it, because the blind spot for the opposite eye is in a different location with respect to the visual world. If you have never found your blind spot before I highly recommend you visit Eric Chudler’s website at the University of Washington(http://faculty.washington.edu/chudler/chvision.html) showing not only how to find your blind spot, but also to demonstrate that your brain can fill in the missing information even in the absence of information from the other eye. Today I am going to discuss blind spots in a more metaphorical sense in the context of the Oedipal Blind Spot.

While Katy Schimert’s sculpture, Oedipal Blind Spot, is indeed a map of Greece, it is designed to simultaneously represent the visual system, and specifically the connection between the eyes the brain. You can see we are looking down from the top of the head as the left eye is above and the right below. How we see is that the visual input i.e. light emitted or reflected off of the outside world enters the eye and this information is communicated on to the brain through what are called axons. In all vertebrate species, these axons cross each other in what is called the optic chiasm, or chiasmus here, just before entering the brain proper. In animals with frontal eyes, where both eyes are seeing much the same thing, the axons actually intermingle here at the chiasm, and approximately half of the axons from each eye goes to each half of the brain, so you have left eye and right eye inputs intermixed on both the left and right sides of the brain. If you were to take this connectivity literally in the context of this sculpture you would see that they left eye axons are represented by red thread, possibly signifying life or the blood line, and the right eye axons are represented by black thread, signifying death or darkness.

Consistent with this idea, you notice that the red thread begins with Oedipus’ childhood or adoptive home, Corinth, and that the black thread is associated with Athens where his is said to have gone into self-exile and died. You will also note that the pathway to the carrion birds of Theiresias, which represent the brain of intuition and mystery, are not intermixed, as the visual projection would be, but entirely black. Furthermore, the pathway back to Thebes is entirely red, indicative of his tie to his birth parents Laius and Jocasta. This failure of the paths to properly intermingle may be the first indication of the blind spot that governs Oedipus’ tragic life. Oedipus was simply unable to integrate the intuitive, perhaps the riddle of the Oracle, with the concrete, which was the identity of his parents.

 

This inability to properly integrate information from different modalities seems to us to be somewhat naïve. You might even say, “well Oedipus is a Greek tragedy – that could never happen to me,” but you would be wrong. Integration of information happens at many levels, such that sensory information becomes increasingly processed and therefore sophisticated along the pathway that it travels to the brain. Take for example the relatively simple – and well understood – organization of the visual system. There are several layers of cells in the eye that process the information from the visual world. Light first enters the eye hitting the detector cells, which we call rods and cones. Rods and cones communicate this information to one or more cells in the next layer, which send the information along to one or more cells in the next layer that then project to the brain. In the brain, the retinal axons communicate to one or more cells in a brain structure called the thalumus. The thalamus then sends projections on to the visual cortex, which is in the back of the brain.

This is the first place where information from two eyes begin to converge, as you can see inputs conveying information from both eyes on single neurons in layer IV of the visual cortex. From there, the cells project to cells in different layers of the primary visual cortex and from the visual cortex on to the secondary visual cortex, and from there to other centers. At each step of this pathway the coding of the information becomes increasingly sophisticated. In the eye, a rod or cone only knows one thing: how many photons collided with it. An individual thalamus cell receives the necessary inputs to determine whether there is a light spot on a dark background or a dark spot on a light background at a particular point in space. A cell in the primary visual cortex interprets information about edges or lines, many can even tell if those lines are moving. Beyond that is such sophisticated processing that we don’t even really understand it, but it seems that our encoding is sophisticated enough even that we have individual cells that can interpret whether or not we are seeing a face.

The point of all of this is that every level of processing is an opportunity for error. Some of the best known errors are agnosias, where an individual is unable to recognize or process a particular modality, such as word agnosia experienced by dyslexics or prosopagnosia the inability to recognize faces. Another type of error is synesthesia which should be familiar to anyone who has read Oliver Sack’s book The Man Who Mistook His Wife for a Hat. In synesthesias, individuals confuse one sensory modality with another such as tasting shapes or associating numbers with colors, which you may have read about in the latest ScientEphic magazine. However, I would like to draw your attention to a completely different sort of misinterpretation of sensory experience and that is of vestibular illusions. Our vestibular sense, or our sense of where we are in space, is conveyed to us through three sensory modalities, proprioception, vision, and sensory input to the inner ear. The advantage of this is that these three modalities can be functionally redundant such that loss of one can be compensated for by the other two. The disadvantage is that any time the input from one of the three disagrees with the input from the others, it can results in vertigo and motion sickness. When the problem is chronic it can be debilitating and even intolerable, and suicide rates among people with chronic vestibular problems is significantly higher than that of the general population. We know quite a lot about vestibular illusions from the experiences of fighter pilots because they fly often in the dark, in the clouds, or in other ways without sufficient direct visual input, and it turns out that vestibular illusions almost exclusively occur in the absence of visual input.

One example is that of the Giant Hand Phenomenon, where a pilot flying a plane begins to very slowly turn in one direction, intentionally or not, which causes the plane to begin to descend because of the reduced lift on the wings. If the turn is of sufficient duration and sufficiently shallow, the sensation (again in the absence of visual input) is one of flying completely level. Because of the overwhelming tendency of the brain to assume the familiar, the pilot sometimes assumes that their instruments are reading incorrectly even if they are not. What is more common is that the pilot recognizes his or her own error and attempts to return the plane to a neutral angle using the control stick. However, in the process of doing so, there is an overwhelming sensation that the attempt to right the plane has resulted, not in righting of the plane, but in banking it in the other direction, which results in the overwhelming reflex to return the plan to its original banked position. Pilots who have experienced this have said that it required an immense effort to try to control the plane because it was as if a giant hand were pressing down on the wing (on the side of the original turn).

There are several other examples of vestibular illusions, but I think this one most nicely illustrates the tension between subconscious and conscious. Even knowing the right answer is not always enough to solve the problem, or in the case of Oedipus, to avoid fulfilling the prediction of the Oracle.

I would like to add here that one of the only ways known to overcome the Giant Hand Phenomenon is for the pilot to let go of the controls of the airplane for a few seconds. When a pilot does so and returns their hands to the controls it is generally much easier to right the ship. When you think about it, the similarity to Oedipus’ condition is striking, given that when he finally discovers his tragic error he relinquishes control of his final days to his daughter Antigone. We have reason to believe that Katy Schimert may identify with Antigone, and this piece may be an attempt to suggest that the resolution of the problems associated with the blind spot may simply be to relinquish control, perhaps to the next generation.

- Lara Hutson, Assistant Professor of Biology

Above images: Katy Schimert’s Oedipal Blind Spot, 1997 (2010); aluminum tape, conte crayon, pastel, graphite, thread, pins. Exhibition copy from the Ursula Hauser Collection, Switzerland; Courtesy the artist and David Zwirner, New York.

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