Alex Hansen

Prof. Paul Grobstein

Neurobiology and Behavior

April 14, 2007

The Color of Vision

Five essential senses of perception, classified by ancient peoples, exist for the human race. The defining terms include touch, taste, hearing, smell, and sight. Despite the lack of consensus that these five senses are the sole physiological methods that exist, generally, each is eternally exhibited throughout the universe. However, there is no guarantee that every individual will possess all five senses, or that every individual will maintain senses that function with perfect accuracy and without deficiencies. Vision is a primal example of one of the five senses that does not remain homogenous across humans, or across all living organisms. Upon looking at a single image, what one sees may or may not be what another is envisioning. Moreover, the individual may be blind and may be thought to not be able to see at all, yet that person may still appear to retain some internal form of vision that may be unknown to those not diagnosed which such blindness. Such differences in vision arise from a variety of causes including genetics, specific life events, as well as evolution. It is through the development of organisms and evolution that the current classifications of vision have been established. While some types of vision are advantageous for particular animals, such might create detrimental effects for a different species. Thus, although sight is a universal term used for one of the five physiological senses, vision is often specific to varying organisms. With such, according to evolution there often exist biological similarities across different species, and thus there must also exist similarities in the vision of these comparable species as well. Through using these evolutionary differences and similarities as a basis, one can examine this physiological classification of sight across different animals. One particular aspect of vision which appears to demonstrate the heterogeneous quality across species, as well as connect the genetic resemblances within such organisms to possible evolutionary explanations, is color. To the eyes of different animals, color has the ability to vary and change, or could even be lacking due to an abnormality in the animals color vision, or due to a type of development specific to that animal. The developed color vision will often provide advantages to that species, as evolution is a process which occurs to allow for the survival of what is considered favorable. As evolution continues forward to the future, current types of vision will be able to change as certain attributes may develop to become more conducive to success.

It is one thing to be told that much of behavior reflects unconscious processing -it is another to actually have that message proven with an actual experience. The breadth and power of the unconscious eluded me until I saw how this level of processing relates to my life. It was demonstration in class involving a checkerboard where differing levels of gray created the illusion of different colors (1) that convinced me unconscious processing affects the way we process the world.
    We had been discussing visual processing for more than a week in the class and thought I understood. I knew that the brain could only interpret certain signals and filled in the rest, I was conscious of it. However during that demonstration, my Unconscious finally kicked in as well and I really understood. The conscious (me knowing what was going on ‘up there’ was working without the unconscious (me actually seeing the effect of the way visual processing works). In my case it took the activation of my unconscious to complete my experience. Although I was not fully convinced of this phenomenon until recently, others have been exploiting it for years, whether consciously or not.

Our understanding of memory is one of the things that make us intrinsically human. Many organisms have memory processes, they learn, they adapt o their surroundings, but humans have the ability to change those functions, to control them. We can choose what we learn and what we don't, we can memorize information and in certain cases force ourselves to omit things from our memory. Our lives are completely based around this function - adults work in a job doing things they have learned to do, children learn in school about things from our past, stories of our past are passed down from generation to generation by memories. Even the basic processes of our bodies utilize systems that have their own type of memory - our bodies, even down to the smallest molecules, "know" what their purpose is (2). This stasis enables us to function at the high level that we do - all parts of the body working together to produce a living, breathing, functioning, and above all remembering organism. Our memory grounds each and every one of us, makes us unique. Every person has different experiences that make their self. It seems that in this sense our selves are dictated by what surrounds us, what inputs come in and how those inputs are automatically dealt with. The problem, it seems, is when the reality of memory can be altered, when memory seems to have a mind of its own.

      In his autobiography, Speak Memory, Vladimir Nabokov describes a rather curious experience: “I present a fine case of colored hearing” he writes. “Perhaps ‘hearing’ is not quite accurate, since the color sensation seems to be produced by the very act of my orally forming a given letter while I imagine its outline” [1] (Nabokov, 381) The  synesthetic experience described by the famed novelist, although unusual, is by no means unique. The phenomena was once thought to be quite rare and was often brushed aside by the scientific community who attributed it to hallucinations and drug use. Recently however, synesthesia has become the subject of much research among neurobiologists. Recent studies have shown that far from being a freak occurrence,  approximately one in twenty people have experienced one of the many different kinds of synesthesia [2][5] .

             In order to be diagnosed with anorexia nervosa, a person must meet the DSM-IV criteria for the disorder. This includes a body weight less than 85% of that expected, a preoccupation with food or feelings of becoming fat, a disturbance in self-image, and the absence of a menstrual cycle in females.  An estimated .5-3.7% of females will meet these criteria—will suffer from anorexia nervosa—in their lifetime (6). Though these prevalence numbers are not as high as many other disorders, anorexia nervosa (AN) remains a serious concern; it has one of the highest mortality rates of any psychiatric disorder (5). But what causes AN? Many studies, and much media attention, have focused on environmental and cultural factors that play a role in the development of AN. But in addition to these factors, newer research suggests that there is also a biological basis that makes certain individuals more vulnerable to the disorder.

Imagine a world in which you had a song playing non-stop in your head and there was no way to stop it. Your brain was constantly in listening mode and the music in your head was always on full volume. This is what it would be like to suffer from music hallucinations. It is normal to hear an occasional song in your head, but generally it eventually goes away because the brain is bombarded with numerous other signals and stimuli that we are able to focus on instead. Music hallucinations occur when a set of neurons in the brain begin to misfire and patients feel as though they are always hearing music, even though in reality there is nothing playing. There is no other symptom of music hallucination and studies have shown that music hallucination tends to be the only psychosis problem in patients, the main concern being that these hallucinations are very annoying.

It’s unlikely that pheromones will ever be used in a pick-up line; however, scientific research has shown that pheromones could play a part in human sexual attraction.  Since the 1980s, when pheromones were discovered to exist in humans, numerous perfume companies have launched marketing ploys to sell people “magic” scents to improve their sex lives.  There is much debate about the potency of pheromones in human relationships, but pheromone research has lead scientists to question our independence in mate selection.  It has also spurred questions about the difference between consciousness and unconsciousness.  How much can we actually control?  That is the question.

A recent study found that the Alzheimer’s disease rate in Asian Indians is only 25% of the rate in the developed world.  While more than 10%  of Americans over the age of sixty five suffer from Alzheimer’s Disease, only 1% of their North Indian peers suffer from the same disease (1).  This finding prompted researchers to dig deeper into understanding why such a disparity exists between the two nations.  Understanding the disproportion of incidents is not a simple task, for the underlying causes and mechanisms of Alzheimer’s disease are not fully understood.

The emergence of species within evolution provides for ecology where differentiation is valued. Species branch off, isolating and defining themselves as different from their predecessors. This is not only true for species in biology. It is a process visible in culture, and in academia. Each field of academia is a self contained species, with individuals sharing a common biology and society of existence. Each species and culture must coexist. Exclusivity between subjects is not possible or even viable. Symbiosis is a mutually beneficial existence; all species exist within an ecosystem. Species exist in a web of interconnectivity which sustains them and the whole. Abandoning connections with others leaves a species, or academic field, dangerously isolated. Interaction, and therefore intercommunication, is essential for the different species to successful survive.

Modern life in the twenty-first century might be defined by the state of sensory overload.  Cell phones and iPods, Blackberrys and computer screens, fast food and designer perfume put our ears, eyes, nose, tongue and skin into overdrive.  What saves us from falling into a tangled web of sensory data might lie in our ability to classify these sensations into distinct categories.  In other words, I might be listening to Fergie while eating a peach while watching Entourage while scratching my leg, but I am comforted by the cognitive awareness that each sensation, although simultaneous, is separate.  Then what of the synesthete, those rare individuals who experience the neurological phenomenon of two or more sensory perceptions from a single stimulus <a href="/exchange/#1">(1)</a>?  Is their condition of synesthesia a burden or an inspiration in this world of overwhelming sensory stimulation? 

    Scientists first documented synesthesia in the 1880’s, when Francis Galton observed that certain otherwise physically normal people experienced specific colors upon hearing specific sounds or seeing specific numbers <a href="/exchange/#2">(2)</a>. Interest in synesthesia then waned as research in psychology focused on behavior rather than cognition, but synesthesia has recently reemerged as both a legitimate and exciting topic of research linking neuroscience, psychology and genetics <a href="/exchange/#3">(3)</a>.  A pioneer in the modern study of synesthesia is Richard  Cytowic, whose research in the 1980’s proposed that synesthetes experience this condition involuntarily, project the experience beyond “the mind’s eye”, maintain their intersensory experiences consistently throughout their lives and are more common in women and non-righthanded individuals <a href="/exchange/#1">(1)</a>.  Cytowic links the cause of synesthesia to a decrease in blood flow and oxygen delivery within the left hemisphere of the neocortex <a href="/exchange/#1">(1)</a>. Also during the 1980’s, Simon Baron-Cohen and his colleagues at Cambridge University proposed that Neonatal Synesthesia (NS), a condition in which humans up to four months in age experience sensory input without differentiating the source of stimulation, is a normal phase of human development.  According to Baron-Cohen, adult synesthesia results from neurological abnormalities that do not reduce the sensory connections of the neonate stage <a href="/exchange/#4">(4)</a>. Indeed, this neurological “abnormality” is estimated to occur in 1 out of 200 people and can manifest in over 100 different types of synesthesia.  Nevertheless, synesthesia is typically an additive sensory condition experienced in one direction: while a synesthete might always perceive the number seven as yellow, the color yellow will not trigger the perception of the number seven <a href="/exchange/#5">(5)</a>.

Among the most exciting recent research on synesthesia have been conducted by Vilayanur Ramachandran and Edward Hubbard of the Center for Brain and Cognition at the University of California at San Diego, who have contributed new neurological evidence to explain the synesthetic experience.  Their research provides further insights into the evolution of thought, language, and human consciousness, and their approach sheds light on the neurological process of cross-modal perception in separate areas of the brain <a href="/exchange/#3">(3)</a>.  They have explored two possible causes: 1) the tendency of bordering brain regions to inhibit mutual activity: when a chemical imbalance blocks the inhibitory neurotransmitter or fails to produce an inhibitor, cross-linking occurs; 2) a genetic component mutates connections between typically segregated brain areas <a href="/exchange/#3">(3)</a>.

 Ramachandran and Hubbard have used the technology of Functional Magnetic Resonance Imaging (FMRI) to compare the brain activity of synesthetes with those of normal perception.  Their lab has traced neural signals traveling by optic radiation from the retina to the area of the brain labeled “17”, an area in the occipital lobe linked to the perception of color, form, motion, and depth.  From “17”, the neural signals travel to an area labeled “V4”, which they propose is the site for cross-linking between color and numbers.  They demonstrate that this “V4” area was highly active in synesthete subjects that perceived white colored numbers against gray backgrounds, while remaining inactive in subjects with normal perception.  They hypothesize that the perception of colors travel to a “higher” area near the junction of the temporal, parietal and occipital (TPO) lobes that is similar to the neurological site of numerical computation <a href="/exchange/#3">(3)</a>.  However, Ramachandran and Hubbard also argue that there are synesthetic subjects that associate certain colors with the visual appearance of the number rather than with the mathematical concept of that number.  That is, these synesthetic subjects did not perceive colors when Roman numeral equivalents were substituted for Arabic numerals that typically triggered colors.  These findings suggest that grapheme-color synesthesia occurs within the fusiform gyrus that is involved with analyzing visual forms rather than abstract concepts.  Yet for synesthetes, in which the abstract concept of numbers triggers colors, the cross-linking occurs between the angular gyrus near the TPO lobes. 

This brief summary of recent research on synesthesia demonstrates that our knowledge of this condition is constantly expanding, and the only safe conclusion that can be made at this time is that gene mutation causes the ever-expanding variations of synesthetic experience.  However, the connection between synesthesia and genetics raise several important questions for future research.  Which gene is linked to synesthesia?  Can synesthesia be cultivated?  And can synesthesia shed light on the profound questions of human experience related to consciousness, language and abstraction?  “Given the right questions, the right experiments and the right patients, the study of synesthesia might illuminate the very questions that have remained in the domain of philosophers” <a href="/exchange/#6">(6)</a>.

Web Resources

1. <a name="1"> )</a><a href=" http://psyche.csse.monash.edu.au/v2/psyche-2-10-cytowic.html ">; </a>; Synesthesia: Phenomenology and Neuropsychology, A Review of Current Knowledge</a>

2. <a name="2"> )</a><a href=" http://www.bbc.co.uk/radio4/reith2003/lecture4.shtml ">; </a>; BBC Reith Lectures 2003, The Emerging Mind</a>

3. <a name="3"> )</a><a href=" http://psy.ucsd.edu/chip/pdf/SciAm_2003.pdf ">; </a>; Scientific American, May 2003</a>

4. <a name="4"> )</a><a href=" http://psyche.csse.monash.edu.au/v2/psyche-2-10-cytowic.html ">; </a>

5. <a name="5"> )</a><a href=" http://psyche.csse.monash.edu.au/v2/psyche-2-27-baron_cohen.html ">; </a>; Is There a Normal Phase of Development, Departments of Experimental Psychology and Psychiatry at The University of Cambridge</a>

6. <a name="6"> )</a><a href=" http://www.neurologyreviews.com/jul02/nr_jul02_mindseye.html ">; </a>;; The Neurology Reviews</a>