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Transcript
Philip Buss Page 1 Philip Buss 12-9-06 Fletcher Scientific Study of Consciousness Term Paper Consciousness: What Good is it? In recent years, a strong emphasis has been put on discovering the origins of humans through the study of evolution. People are intrigued by the idea that their extremely complicated bodies evolved from lower life forms through a completely natural process. Now, this idea is being applied to the human mind in the form of evolutionary psychology. How was our consciousness created through natural selection? A more fundamental question is “Why was it created?” The theory of natural selection says that our bodies were designed for optimal functionality. Therefore it is only reasonable to say the same of our minds. This subject, however, is much harder to study; there are no fossil records directly indicating the evolution of the mind. This paper will examine some possible explanations for how and why the mind was created, focusing on neurobiological evidence as well as the role of social developments on the creation of the modern mind. The study of brain processes has given scientists some useful insights into how and why the mind evolved. Multiple lesion studies of the human visual system have revealed an extremely intriguing fact; as stated by Cristof Koch, “there are two – at least two – visual systems in your head…One is for conscious seeing, and one is for doing visual-motor actions” (Moffett, 2006, p. 81). An example of this is the phenomenon Philip Buss Page 2 known as blind-sight. Blind-sight is the unofficial term for people who are technically blind and yet show signs of some visual capacities. The neuroscientists Milner and Goodale have done extensive research on patients with different types of brain damage which have altered their visual systems. (Milner, Goodale, 2004). The first patient, named Dee Fletcher, received brain damage from carbon monoxide asphyxiation. Dee is unable to recognize objects, even though she is able to “see” color and texture. This form of blindness is called visual agnosia. Despite her being incapable of identifying (perceiving) objects, her motor responses to visual stimuli are perfectly normal. She is able to navigate around objects when walking, accurately pick up objects, and post her hand through a rotatable slot (Milner, Goodale, 2004, p. 18-20). Another patient, studied by neurologist Rudolph Bálint in 1909, suffered brain damage due to a massive stroke (Milner, Goodale, 2004, p. 32-33). This man’s disorder, called optic ataxia, is fundamentally opposite Dee’s. He has perfect perception, in that he can see objects and accurately describe them as well as their orientation in space. In other words, his visuospatial skills are intact. However, when told to pick up an object in front of him, he shows complete incompetence. He gropes “blindly” toward an object which he can see perfectly. His visuomotor abilities are completely impaired. A very interesting discovery was made in a recent experiment performed on a patient with optic ataxia. When the patient was asked to point to spots of light flashed on a screen, she was very inaccurate, as expected. However, when asked to wait for five seconds after the flash had come and gone, she was much more accurate (Milner, Goodale, 2004, 80-81). This remarkable result demonstrates that this patient’s motor abilities are only restricted when asked for an immediate, reflexive response. When asked to wait and consciously Philip Buss Page 3 plan it out, she didn’t seem to be impaired. The act of planning and internally visualizing where the spot had been must have used separate brain processes than the ones normally used in quickly responding to visual stimuli. These two case studies reveal that there are indeed (at least) two visual systems in the brain. The first is the one responsible for conscious perception (which was absent in Dee Fletcher) and the second is responsible for motor responses to visual stimuli (absent in Bálint’s patient). Using fMRI scans, scientists were able to determine that the processes in the brain which lead to conscious perception are located in what is called the ventral stream, while the processes leading to motor responses are in the dorsal stream. The dorsal stream leads from the occipital cortex up over the top of the brain to the motor strip, which controls body movements. The dorsal stream has been called a “zombie system,” meaning it leads to motor responses without needing any conscious perception. The ventral stream, however, is conscious, because it leads to more complex representations (conscious perception and awareness). The ventral stream, which runs from the occipital cortex along the bottom of the brain, goes through more complicated, specialized brain structures such as the fusiform gyrus (responsible for facial recognition) and the amygdala (responsible for raw emotions) and eventually connects to the temporal lobe, where memories can be formed. The ventral stream appears to be more sophisticated than the dorsal stream, and seems to contain many of the elements of consciousness. Why then is it necessary (or useful) to have two separate systems? Neuroscientist Umberto Castiello found in his experiments on reaction time that the dorsal stream acts much faster than the ventral stream (Blackmore, 2004, p. 39-40). Philip Buss Page 4 Reflexive actions occur well before any perception occurs. According to Cristof Koch and Francis Crick, “It is a good evolutionary strategy…to have some fast, stereotyped reactions and processes in addition to a slower, integrative function like consciousness. With such a schema, consciousness can react to new and evolutionarily unanticipated circumstances while not having to dirty its hands with the mundane work of survival, which it can leave to the zombie modes” (Moffett, 2006, p. 81). In this interpretation, the dorsal steam developed first and was responsible for simple reflexes like running away from a predator or avoiding an object while walking. The ventral stream evolved later, and is capable of overriding the hardwired dorsal reactions in special circumstances. In most instances, the visuomotor reaction is good enough to handle the situation. However, more complicated scenarios may necessitate the use of conscious thought. Animals with such abilities would have been better able to survive, thus selecting for the possession of these two visual systems. Still, why should we have a conscious and an unconscious system? Why not just have a single, more capable conscious one? Neurobiologist John Allman relates this dilemma to a power plant he visited in the 1970s. He was surprised to find that the plant was controlled not by a single, modern computer system, but by multiple systems, including outdated technology run on vacuum tubes. He asked if it wouldn’t be more efficient to have a single, more advanced system (the answer is undoubtedly yes). However, he was answered “that the demand for power had always been too great for the plant ever to be shut down” (Milner, Goodale, 2004, p. Philip Buss Page 5 47). Due to the high demand for power, there was never any time to shut down and redesign the whole system. This is very similar to the two systems in the brain. Originally, there was only the dorsal stream. Then, due to the evolutionary benefits of having conscious perception, the ventral stream was added on top of it. There was never any time to “overhaul” the whole system; simply more hardware was added. This is why we still have an unconscious aspect of vision. The next question we must ask is, “If consciousness is such a useful invention, then why are its capabilities so limited?” Even though consciousness has many valuable uses, it is limited to “one-thing-ata-time.” Bernard Baars, a proponent of the Global Workspace Theory of consciousness, asks us why the brain, which is capable of such complex processes, can only consciously handle one thing at a time. Baars answers that a human cannot have two conscious representations at the same time because consciousness is a global message to the entire nervous system, and only one such message can be present at a time (Baars, 1988, p. 348, 350). This is similar to what Antonio Damasio has termed the “movie-in-the-brain.” “This ‘movie’ is a metaphor for the integrated and unified composite of diverse sensory images…that constitutes the multimedia show we call mind” (Damasio, 2002, p. 7). Our consciousness is undeniably “seamless” in its depiction of the world around us. We cannot really be aware of two things at once. Crick and Koch believe that “it may be more efficient for the brain to have ‘one single explicit representation,’ once and for all, rather than sending information, in tacit form, to many different parts of the brain” (Blackmore, 2004, p. 246-247). The reasons for having a single unified conscious experience are strictly functional. It is important for a person to have one complete representation of the world rather than multiple fragmented ones. Otherwise, it would be Philip Buss Page 6 very difficult to make a coherent picture of one’s surroundings. So far, only the neurobiological aspects of conscious development have been discussed. Now we will move on to the social aspects of this. It is easy to see the benefits of unconscious brain processes. As put by Steven Pinker, “You don’t need an evolutionary biologist to tell you that depth perception keeps an animal from falling off cliffs” (Pinker, 2002, p. 52). It is trickier, however, to see the purpose of consciousness: “But with other aspects of our mental life, particularly in the social realm, the function of a faculty is not so easy to guess. Natural selection favors organisms that are good at reproducing in some environment. When the environment consists of rocks, grass, and snakes, it’s fairly obvious which strategies work and which ones don’t. But when the relevant environment consists of other members of the species evolving their own strategies, it is not so obvious” (Pinker, 2002, p. 52). Social developments complicate natural selection – the actions of one organism affect the life of another. The basis of natural selection is the passing on of successful genes from one generation to the next. If all organisms are devoted only to themselves and their families (similar genes), how is it that complicated social interactions such as cooperation evolve? The simplest answer is that cooperation must aid the individuals in passing on their genes. There is no “greater good” - this is only an illusion. Any ecosystem consists of a bunch of independent organisms trying to procreate. All social developments such as cooperation, non-violence, and monogamous relationships must somehow benefit each organism involved. Furthermore, these developments require the ability to perceive and Philip Buss Page 7 understand other organisms (conscious perception) and then to use that ability for personal gain. The advent of social interactions likely created a large demand for new, more integrated and more flexible processes, which eventually materialized as consciousness. In an ecosystem filled with competing organisms, the ability to understand this environment is extremely beneficial. According to Pinker, another reason why consciousness must be useful is that conscious organisms have it from birth. Consciousness is not “learned” or “formed”. There obviously has to be a survival benefit to possessing consciousness, for “[i]f our minds were truly malleable they would be easily manipulated by our rivals, who could mold or condition us into serving their needs rather than our own” (Pinker, 2002, p. 5455). Therefore consciousness must have some inherently useful properties which are present from birth. Despite the benefits of having consciousness, it is possible for simple organisms to live perfectly well with nothing but zombie processes. Why is it then that humans are so dependent on consciousness for survival? Daniel Dennett claims that simple organisms have “no need for consciousness” (Moffett, 2006, p. 214). However, “once creatures started to move around and interact with each other, creating more complicated problems for themselves and one another, Mother Nature (‘otherwise known as the process of evolution by natural selection’)…began to come up with more complicated solutions to give her offspring a leg up in the fight for survival” (Moffett, 2006, p. 214). In other words, the advent of social interactions necessitated the ability to anticipate, sense, and plan, all of which are constituents of consciousness. While zombie processes Philip Buss Page 8 work well enough for the survival of a single organism by itself, the complications arising from interactions with other organisms require something more. Now that we have seen some reasons for consciousness, let’s look at when it may have evolved. Surely there must be some point at which animals first attained conscious thought. Unfortunately, this is sort of like the “chicken or egg” predicament. Daniel Dennett “doesn’t think there’s a clear place where you can draw a line above which everything is conscious and below which everything isn’t” (Moffett, 2006, 214-215). Since we can’t come up with a clear distinction, let’s try a broader perspective. William Calvin is confident that the human mind was shaped into what it is today during the short periods between ice ages. According to Calvin “climate is fickle; ‘sudden-death playoffs’ can happen within a matter of a decade or so. Abrupt climate change makes versatility, often a virtue, a necessity” (Calvin, 1991, p. xiv). As we saw with the ventral stream in visual processing, versatility is one of the main benefits of consciousness. Calvin points out that somewhere in the period of shifting ice ages, hominids turned into humans. His theory is that it was during the short “boom times” in between ice ages that humans developed large brains (and subsequently consciousness.) In this essay, we explored various reasons for having consciousness, as well as how it might have come into being. Studies of the visual system have shown us the usefulness of conscious perception as well as why we have two separate processing streams for visual stimuli. We have also seen why the brain strives to create a single, unified experience (movie in the brain) – it allows a coherent representation of the environment to form. We then looked at how the advent of social interactions sparked the beginnings of consciousness. Finally, we put it in perspective by giving a theory on Philip Buss Page 9 when this emergence took place. Consciousness is perhaps the last great biological mystery. Despite its deep involvement in our lives, its function is still largely mysterious. One philosophy, known as mysterianism, says that complete understanding of the human mind is unattainable. I, however, feel that with enough people dedicated to studying it, the mysteries of consciousness may one day be revealed. Philip Buss Page 10 Bibliography Baars, Bernard. A Cognitive Theory of Consciousness. New York: Cambridge University Press, 1988. Blackmore, Susan. Consciousness an Introduction. Oxford: Oxford University Press, 2004. Calvin, William. The Ascent of Mind. Bantom Books, 1991. Damasio, Antonio. “How the Brain Creates the Mind”. Scientific American. 2002: 4-9. Goodale, Melvyn; Milner, David. Sight Unseen. Oxford: Oxford University Press, 2004. Moffett, Shannon. The Three-Pound Enigma. New York: Algonquin Books, 2006. Pinker, Steven. The Blank Slate. New York: Penguin Group, 2002.