What does reality look like?
What would "reality" look like outside the brain?:
Variations in Perception and their Significance
Ever had a conversation with a friend that goes something like, "How can you eat that?," you ask as she piles ketchup and mustard on her french fries, “How can you not? It tastes great!” she replies. Or, ever wonder why people look disgusted when you claim to actually LIKE eating something like, say, brussel sprouts? Ever have an argument with someone over whether two colors match or not? Do people compliment you on your abilities to paint a realistic picture of a sunset?
The more we understand about the nervous system the more these type of exchanges make sense. We experience and make sense of the world via our nervous system. Our nervous systems differ from one another—differences that may be due to a lot of things, including genetics, experience, random events. Because our brains are different, we therefore experience the world differently.
Let’s look at a few cases where differences in perception can be directly related to nervous system differences among people. Then let’s talk about how we might generalize from these and what it all implies about the notion of “reality”.
Seeing: Color Vision, or Is color in the world or in the brain?
What is light? Light is electromagnetic radiation. It is emitted from the sun (pure sunlight is called "white light"). White light is a mixture of waves of varying wavelengths. When it hits an object, what object absorbs some of the lightwaves and reflects the rest. The light that is reflected is what our eyes detect.
The retina on the back of each eye contains neurons (photoreceptors) that respond (via electrical signals) to light. Among the types of photoreceptors are rods and cones. Cone cells are the first step in the nervous system that gives rise to the experience of color (phototopic vision).
There are three types of cone cells in the eye, each of which is tuned to respond most strongly to a particular wavelength: short-, medium-, and long-wavelength cones (S-cones, M-cones, L-cones, respectively).
S-cones respond to light around 400-550 nm in wavelength, with the highest sensitivity around 445 nm. M-cones respond to light around 400-675 nm, maximally at around 535. Finally, L-cones respond at around 450-700 nm, maximally at 575 nm.
The important things to note are that the absorption range of each type overlaps with the others so most wavelengths of light activate not one but two or more, and that all a single cone essentially does is capture light and report something about its relative wavelength. A single cone does not tell you anything about color. So where does color come from then?
The experience of color comes first from the combined activation of all three types of cones. A wave of a particular length will activate a unique ratio of short:medium:long cones. For example, light of wavelength 535 will yield a maxium response from medium wavelength cones; however, both short and long wavelength cones will still respond, just not as intensely.
People experience colors differently, whether only slightly or drastically, due to variations in their nervous systems. One way that this can arise is differences from one person to another in the absorption ranges and maximum peaks of wavelengths that cone cells respond to. That is, a light wave of length x will yield a different ratio of responses from short-, medium-, and long-wavelength cones.
In the illustration above, the same lightwave (579 nm) is reaching the woman’s and man's eyes. However, due to differences in their cone cells, they may experience different colors. The woman might say "I see a bright green color", while the man might say "I see a green color tinted with blue".
Is someone who is color blind, really color blind? No, because color is experienced by the brain. Color is not a property of the material world. Wavelength is, but color is not. People who are red-green color blind, for example, simply experience the same wavelengths differently.
It might seem that trichromats (normally sighted) are superior to dichromats (red-green color blind, among other types). When shown a color photograph, trichromats may be able to more easily discern certain objects. In a black and white photo, or to dichromats, certain objects may be difficult to discern if an object's luminance is similar to the background or if the illumination casts random shadows. In this case, normally sighted individuals are advantaged. However, there are certain cases where being a dichromat may actually be advantegous. Colorblind individuals have been thought by some to be superior at penetrating camouflage, whether in military combat or in the natural world. The first study that empirically tested the idea that colorblind individuals may be more advantaged in certain ways found that dichromats were superior to trichromats at detecting texture and shape than a normally sighted group.
We all have food preferences, food we like to eat and food we don't. But is this a matter of preference or do foods actually taste different to different people? It seems that at least part of our preference actually has to do with different taste sensations and resulting from differences in the nervous system. But how are these preferences influenced by our own unique experience of taste? Research on tasting has revealed that taste is more varied than once thought. Scientists have designated three categories based on subjective reports of taste sensation as well structural differences in peripheral anatomy: non-tasters (25% of the population), tasters (50%), and supertasters (25%).
The perception of taste begins in the tongue. Our tongues contain hundreds of bump-like structures called fungiform papillae. Within these are our tastebuds, stuctures that contain gustatory receptor cells. These receptor cells transduce signals and send information to peripheral neurons. Each receptor cell has a hair-like structure that protrudes from the taste pore and binds molecules in the saliva. When a food molecule comes in contact with a hair, the receptor cell signals information (via neurotransmitters) to neurons leading to the central nervous system and into the cortex.
The term supertaster doesn't imply that food necessarily tastes better (or super), rather it means that supertasters seem to experience more intense and nuanced sensations in response to particular compounds (or flavors) in food. Put another way, they have a heightened sensitivity to taste relative to others in the population. Researchers have found a correlation among supertasters and the reported sensitivity to a compound called propylthiouracil (PROP). PROP is frequently used as a test for supertastering. It is flavorless or mildly bitter but still tolerable to most people (non-tasters and tasters) but is perceived as very bitter and intolerable (think gag reflex) to supertasters.
A few of the common foods that supertasters find aversive are coffee, broccoli, brussel sprouts, and dark chocolate. One super-taster writes:
I am not a freak. I am not picky. I am not hard to please, inflexible, or timid. I am… a supertaster. Foods like coffee and mustard literally make me gag... I am always willing to try new foods, and I eat all sorts of strange things (snails, calamari, oysters, pop tarts, kipper snacks). I love different ethnic foods (Chinese, Italian, Lebanese, Greece-y) and am not a restaurant snob. However, there have always been certain foods that I cannot eat. Not "will not" eat... cannot eat, at least not without having to control the gag reflex... [T]here is a list of foods that I cannot eat. I regularly revisit this list, just to see if things have changed, and they never do.
Supertasters have been shown to have a higher density of fungiform papillae their tongue, and hence tastebuds, which are located within the papillae. Taste, bitterness, sweetness, and so forth, then, is not an inherent property of compounds that elicit such sensations, rather taste sensations are made up by the brain. Differences among individuals (the number of tastebuds being only one example) lead to differences in taste perception.
Touch: Insensitivity to Pain
Would it be reasonable to think that people also experience differences in touch? Yes, in fact a well-documented case is that of insensitivty to pain. The most common and studied case is congenital insenitivity to pain with anhidrosis (CIPA). This arises when an individual inherits from both parents a mutated gene that is involved in nerve growth and survival. The insensitivity to pain is accompianed by a conscious insensitivity to temperature, as well as an unconscious one which leaves the body unable to regulate its temperature. Receptors in the skin include mechanoreceptors (being hit, pinched), thermal receptors (feeling something that is hot or cold), chemoreceptors (itch, acidity) and finally noicioreceptors. Nocioreceptors are the receptors that respond to "noxious stimuli", feelings that the brain consciously perceives “painful”—aversive and damaging to the body. In a particular case of CIPA, invidiuals are lacking these receptor cells. Thus, no peripheral neurons to detect changes to the skin means no sensation of pain in the brain.
Other variations in experience
Color vision, tasting, and pain perception are two examples of obvious differences among individuals for which there are well-described and correlated variations in the nervous system. There are many other ways individuals seem to experience the world differently, and we can imagine that they too are in some way a result of differences between nervous systems. With research into these areas it is likely that such differences will turn up.
People experience differences in hearing, for example. As we age, we become less able to detect higher frequency (pitched) sounds. There are also clear differences between people in how sounds are perceived. Oliver Sacks writes in his book Musicophilia:
Sir Frederick Ouseloy, a former professor of music at Oxford, for example, "was all his life remarkable for his sense of absolute pitch. At five he was able to remark, 'Only think, Papa blows his nose in G.' He would say that it thundered in G or that the wind was whistling in D, or that the clock (with a two-note chime) struck in B minor, and when the assertion was tested it would invariably he found correct." For most of us, such an ability to recognize an exact pitch seems uncanny, almost like another sense, a sense we can never hope to possess, such as infrared or X-ray vision; but for those who are born with absolute pitch, it seems perfectly normal.
Despite what you may have learned in school, there are other ways to experience the world than through the five senses of seeing, hearing, smelling, tasting, and touching (see Perception: From Five Senses Through Synesthesia and Beyond). Proprioception is an example of another way we experience the world, and in particular, ourselves. Proprioception is what allows us to balance ourselves when we stand up, walk, and run. Propioception also allows us to sense where our body is. If you close your eyes, you still know how your body is positioned. This body sense arises from a number of sensory parts, including the vestibular system (the vestibular appartus in the inner ear), mechanoreceptors, and even your eyes. The vestibular apparatus gives a feeling of "up" and "down" (relative to the earth) because it senses the pull of gravity. Thus, you know if you are upside-down or right-side up. It also produces the sensation of movement and the spatial orientation of the head. Mechanoreceptors in joints and muscles respond to pressure and distortion or angle of the joint or muscle, and allows you to know how your body is positioned.
You may be wondering, how could people possibly differ with respect to proprioception? Have you ever gotten car sick? Or maybe you've never experienced motion sickness? Car sickness may occur in some people particularly when they are reading. As the car is moving, the inner ear detects that your body is in motion. However, your eyes, fixated on the book, register the book as not moving. This conflict of sensory input to the brain is likely what causes the feeling of uneasiness. What is interestng of course is that some people get car sick and others do not. Do you know someone who is very clumsy? Uncoordinated? What about someone who is very adept at physical activities, like gymnastics or pole vaulting? Can you imagine that these differences are at least somewhat traceable to varities in parts of the sensory nervous system contributing to proprioception?
A phenomenon that occurs among astronauts is space sickness. If you were in orbit you might feel disoriented because the vestiublar system senses the pull of gravity, but in orbit there is no gravity. Therefore, your brain isn't getting any information about your body's position. When asked to close their eyes, astronauts cannot say which way is up and which is down because they then have neither input from the visual system nor the vestibular system. Even under extreme circumstances like being in space, differences exist between individuals. Some astronauts experience intense sickness including vertigo and violent vomitting, others experience only mild headaches, and still a small percentage are apparently immune to space sickness (see Mixed Up in Space).
Thus far, we've discussed how people differ with respect to a particular sense. That is, while one person may experience a color as "more blue", someone else might experience it as "more purple". What if someone said they experienced it as both blue and salty? You might be thinking “Huh?”. But for some people the notion of experiencing a single stimulus in more than one sensory modality makes perfect sense. Synesthesia is "the mixing of the senses" and occurs when a stimulus (light, for example) involuntarily elicits a sensation in another sensory modality (sound, for example). A synesthete might see the color orange in his or her field of view when in pain. Another synesthete might taste chicken as pointy. The neurobiological underpinnings of synesthesia haven't yet been fully described, but comparing synesthetes demonstrates how much variation there can be among people.
Reality outside the brain?
All perception and experience is a function of the brain and the rest of the nervous system. Since nervous systems differ among people, people perceive and experience things in different ways. My “reality” is much different than your “reality”, whether in subtle or extreme ways.
But is there a way to know what “reality” is really like? What would the physical world be like if perceived outside of the framework of the brain? That is, how would things look (taste, sound, feel like) if our brains did not construct our experience? Since color is a construction of the brain, would the world look colorless? Without a brain to construct our worlds, would reality be “a bloomin’ buzzin’ confusion”? Or perhaps noisy?
|Colorless?||A bloomin' buzzin' confusion?||Noisy?|
There isn’t any way we could get outside our own brain and view the world, but maybe some perceptions more accurate or truer than others? Maybe some better than others?
There is much more to the physical world than what we as humans experience. Consider other species and their nervous systems. Some fish and other aquatic animals have evolved to sense electric fields, some for prey detection and others for finding mates. Some animals, such as sea turtles, bats, and lobsters, sense magnetic fields. Because we as humans do not detect electric fields or magnetic fields does not, however, make them any less a property of the physical world or one sense better than another. Different senses have evolved due to both random chance as well as how much a particular sense has allowed an animal to thrive in it’s own environment. As an example, the fact that salt water is a better conductor than air may have influenced the evolution of electrosensitivity in some fish and other aquatic organisms.
One might be tempted to consider color vision better than blindness, maybe because color blindness is much less common than color vision. Does a trichromat have a more accurate perception of reality than a dichromat? Maybe the concept of “reality” should be done away with because all that “there really is” is the physical, material world. A trichromat’s experience of light is not any truer or more accurate than a dichromat’s experience because color is not out in the world but rather in the brain.
There many properties of the outside world that we don’t understand or we're not aware of simply because the sensory systems to sense them have not evolved. Indeed, there are an infinite number of ways to sense, experience, and explore the world that have not (or not yet) evolved.
What is reality like? Is one person’s experience more real or better?
Maybe these questions are meaningless. The only way in which we can know the world is through our personal experience, which is a function of our own, unique brain and nervous system. Other organisms get along with brains and their perceived worlds, which are all different from each other. This implies that the same is true of ourselves–the worlds which we construct differ, sometimes radically and sometimes subtely, from the world constructed by others. There is not in principle a correct or superior way to perceive and experience the world.
Imagine that we could experience the world outside of the brain. Perhaps what we would find wouldn’t be very interesting. Maybe it would just be a bunch of noise, and noise wouldn’t be interesting because it inherently has no meaning. It is the brain that makes meaning out of noise and everything else. And what is meaningful thus depends on one’s unique brain and nervous system.
The bottom line?…
And even our conceptions of what the world, or “reality”, would be like are themselves in the brain.
Continuing research into variations between nervous systems
Variations in Perception of Bitter Go Way Back (New York Times)
Posted by Laura Cyckowski and Paul Grobstein, Jul 8 2009.