Biology 202 Neurobiology and Behavior Spring 2001

Lateral inhibition, the brightness/color distinction, and color processing itself all lead to some important conclusions about "perception" (the "picture in your head") and about how it is achieved by the nervous system. Among them is a possible answer to the old question "if a tree falls in a forest and no one is around, does it make a sound?". The answer, it was suggested in class, is "no". What do you think of the logic (observations and interpretations) used to reach this answer? about its implications?

Lateral inhibition, the brightness/color distinction, and color processing itself all lead to some important conclusions about "perception" (the "picture in your head") and about how it is achieved by the nervous system. Among them is a possible answer to the old question "if a tree falls in a forest and no one is around, does it make a sound?". The answer, it was suggested in class, is "no". What do you think of the logic (observations and interpretations) used to reach this answer? about its implications?

Actually, as I write this now, it seems even less convincing than when I read it, so I'm probably missing something important. Churchland raised some good counter-arguments to it, but I don't think I fully understood them on a first pass. It seems to me, though, that there's some fundamental problem with the analogy. For one, of course, the images created by the flight simulator are not in the computer; they're in our heads, so they can't be to the computer what perception is to us. We've already seen other reasons why current computers are bad analogies for the nervous system: passive current flow versus digital information, for example.

Anyway, this is just another interesting way to look at questions we've already looked at and continue to look at. It definitely relates to the tree question, too. Of course it makes no sense to investigate a flight simulating program by looking at the wiring of a computer, but it may still make sense to understand the images by looking at our wiring, just as it may not make sense to question the reality of sound, but it may still make sense - even more sense, in fact - to understand the sound in neural terms.

I was also looking at an interesting study (published in Development) that focused on the development of lateral inhibition from primary neurogenesis in zebrafish. The study found that competitive lateral inhibition was a way to explain how primary neurons emerge from early proneural cells of the zebrafish. This seemed interesting to me, because it shows that lateral inhibition (and associated genes) play a strong role in the development of complex nervous tissue.

The last thing I wanted to talk about was the issue of a tree falling in the woods. I don't know if I believe that it doesn't make a sound if noone is around. The air molecules are still disturbed and noise is created. I don't understand why there has to be someone present to "hear" the noise. Just because we are not around to experience, does that mean it doesn't happen.

A tree falls and makes a sound because the molecules in the air vibrate. When they vibrate they knock into one another and that is what sound is. The reason we hear it is that the molecules vibrate into our ear are magnified on the timpanic membrane (ear drum) and move on to the cochlea. In the cochlea, the hair cells are moved by the liquid that surround them which itself moves as a result of the vibration of the membrane. When a hair cell moves enough it creates an action potential on the auditory nerve. That goes into the brain and we percieve sound. So all that is really going on is that a bunch of molecules are vibrating when the tree falls. I don't see how one can say that the brain makes up the perception of sound unless I am totally off base on auditory conduction. (It has been 2 years since I studied this stuff.)

Now back to the tree falling... whether someone is there to hear it or not the molecules still vibrate and so they still make a sound. So I say the answer to the question is yes the tree still makes a sound. The only question is does it vibrate the molecules near your ear, not does it vibrate the molecules.

So the tree falls in the forest and it bumps into things on the way and finally crashes against the ground. Sound waves are produced aplenty and race off in all directions. As you stand there watching this, those waves ricochet off your eardrums etc. etc. (for more detailed description, see Elizabeth Gilbert’s entry) and you hear sounds. Sound to us, is in fact, those waves of molecules as they bounce into each other, traveling from the source of the disturbance to our auditory sensors. It is a perception. Two things are needed to experience the sound, the waves themselves and something that can translate those waves. So without the auditory sensors, will we have sound at all? I tried to envision this. In my mind, I tried to sneak up on a falling unsuspecting tree in the empty forest. To my dismay, I could hear the cracking and snapping every time, the waves are there and the auditory sensors are there and when the two come together I hear sounds. To try to prove or disprove this query is impossible because we experience sound the moment we look in on the falling tree in the forest. And if we don’t look in, how will we know?

But that isn’t important you say, the sound waves are still being produced where we are there or not. So what if we don’t experience the sound, mechanically, it is still there. Well, mechanically, the waves are there, but sound to us is what we make of those waves. Without something that can translate, or even sense those waves, we don’t hear sounds. So does that mean in the forest devoid of witnesses (human or animal), the tree only makes the potential for sounds but not a sound? I enter the forest of the falling tree, this time I am deaf. The tree falls and I hear nothing, though I know the waves are there, I just can’t pick them up. Maybe there is no sound when there is no one to perceive it, after all. If there is nothing to sense the waves that would be sound, the waves won’t be sound.

The answer to this, one of the greatest philosophical questions, depsends on how one perceives reality. If reality is independent of perception, then the tree in the forest will make a sound regardless of whether someone is there to hear it or not.

However, when considering reality to be determined by one's perception, then the tree did not make a sound when no one was present in the forest to hear it. Hence, the way we perceive sound is just like the way we perceive color, both are functions of the brain.

When a tree falls in the forest, sound waves will always be created. If we aren't there to witness the tree falling, then the sound waves are just waves and will not be translated into sound. It is interesting to think that sound depends on us. If we are not there, then sound (or noise) will not exist. What about animals- does a different type of sound exist for them? Animals must then perceive a different type of reality than we do. But then whose perception of reality is more accurate?

I guess the same arguements that are made for sound and color can also be made for silence. Silence must also then not really exist, it must just be a clarification for us of what we cannot perceive.

So what happens when no one is around? Does it really matter? If you or anyone is not there to witness it, does it really have any effect? Isn't this what perception is all about? You have to be there and experience it for it to carry any meaning. If you aren't there, then whatever sound it makes while moving the molecules of the air and those that compose the tree is of little consequence.

It seems that most people see perception in terms of all the senses. We are dependent on touch, taste, sight, sound, and smell to understand the world around us. Whether this reality is independent of our perceptions (existing outside of us, not just "the picture in our brain") is still debatable in some of our minds. In talking about the tree falling in the woods question several people brought up the possibility of a deaf individual being present when the tree fell and the implications of this. Such a situation got me thinking about The Who's rock opera "Tommy." In it, the main character, Tommy, witnesses a traumatic event which renders him deaf, mute, and blind. He is a lost cause for his family until one day his cousin places him in front of a pinball machine and low and behold, he's amazing at it.

So, rock music and fantasy aside, what does "Tommy" have to do with anything we're talking about? Tommy is left with touch, taste, and smell... senses that would not seem to be good for pinball playing, a game that utilizes hand-eye coordination. Tommy's perception of the world around him does not include the blinking lights or the flippers of the pinball machine. And, as with the tree falling, do these things exist if he cannot experience them? As the song goes, "he's a pinball wizard; there's got to be a twist!" But maybe not. Maybe perception is as much about what isn't there as what is... Tommy's other senses can compensate for what he has lost. He can "see and hear" the machine, probably better in fact, without his eyes and ears. I don't think perception is always about what's in front of you. It's also about the gaps that you have to fill in. If a tree falls and no one hears it, it doesn't make a sound. If a tree falls and a deaf person doesn't hear it, it doesn't make a sound. In the second case,the absence of sound perception doesn't matter. A deaf person could feel the wind, vibrating ground, etc. created by a falling tree. The question is not does the tree make a sound, but does the tree fall at all.

Thinking about my interactions with every person I?ve met has reminded me of my recent struggle to identify and define a soul. As I?ve pursued my interest in neurobiology and behavior (a pursuit triggered by conventional ?soul-searching,? although the interest was already there), I?ve become increasingly convinced that there is nothing ethereal that determines my behavior or my emotions and nothing internal to Me that will survive my death, the two definitions that I think are most usually used for the soul. Yet I continue to have an emotional need to believe that there is something immortal [a need that seems to be shared by others in Bio 202], that a soul does exist, but that its definition needs to change. My current vision is that if the ?soul? does not exist internally, it must exist externally; and if it?s not specific to Me, it must be shared ? a common soul, if you will. I conceive of the soul now not as something that exists in a person, but as something that exists in the interactions among people. I?m not saying that interacting with people feeds my soul, restores my soul, or has any other platitudinous effect on my soul; I?m saying that the interaction among people is the soul. Moreover, to speak of ?my soul? is, in this construct, no more accurate than to speak of ?my sunlight? or ?my sound;? the soul is simply another input that affects my behavior, just as seeing light or hearing sound affects my behavior. In turn, my behavior also affects the soul, and thus how others respond to the soul, just as clapping my hands or lighting a candle can affect how others respond to sound and light. The effect of my behavior on the soul ? that is, my interactions with other people ? radiates not only through space, but also through time; in this way, it?s as immortal as humanity. My behavior in interacting with people ripples through generations of the soul as a stone ripples a pond. (I think I?m borrowing that imagery from some poorly written, made-for-TV movie I saw once, but it works for the time being. And I didn?t promise great writing here, either.) Individuality is preserved even in this concept of a communal soul because the effect any single person has on the soul and his or her response to the soul may be as unique as hair color, musical preference, or favorite pizza toppings. True, the effect of this soul on any person?s behavior is mediated by neural activity, but its effect seems as real as any other input ? visual, auditory, tactile ? that determines behavior. That?s how I see it now, though it?s likely to change. One of my most firmly held beliefs is that beliefs should be constantly re-evaluated in the face of new information. I should also note that I?ve never formally studied philosophy or religion, so if it seems that I?m passing someone else?s ideas off as my own, it?s only because I didn?t know someone else had these ideas first.

Another issue with the lateral inhibition network is the effect is has upon our perception. It kind of disturbs me that my eyes control so much of what I see. Also, my brain creates the rest of the image. This implies that my brain will imagine a scene I want to see. So the world could be completely different than what I am seeing. What would happen if my lateral inhibition network were changed? Could placing another person's eyes in my head make me see a "new" world?

A lot of questions were raised in my mind this week. I don't know if any of them can be answered, but they do interest me.

In class last week we talked about the blind spot in the eye. The blind spot is something we cannot see unless we do specific exercises. On a conscious level, we do not even realize we have the blind spot because our brains fill in the blind spot with relevant information. Other animals have this blind spot, but only humans are capable of understanding why we have the blind spot. Human brains function at a higher level than other animal's brains--this is why our frontal cortex is so big in comparison to other animals. Because of this high level of functioning humans are able to make sense of, talk about and question the blind spot and other processes that occur in our body and the outside world.

Humans are able to make sense of their actions. Humans can think and communicate. This is how I understand the I-function. It is necessary because it helps in understanding our actions, our interactions, the outside world, and ourselves. Yes, there are things are bodies do, such as the blind spot and the brain making up for it, that are not part of the I-function. But, without the I-function we would not be human.

Do individual differences exist in this making of reality? Does everyone see things a tiny bit differently but the differences are so small that they don't seem to matter at all. How can people vary so much in so many different dimensions yet we all seem to have an implicit feel for what is red and what color grass is? I feel like this discussion lends itself to thinking about creativity. Are those who are creative those who tend to see the world a tiny bit differently, those who vary a little from what our nervous systems have decided upon as reality? Maybe so.

It seems that the ability for humans to recognize faces, even after people have aged and changes, is an argument for hierarchical processing. That is, there is still a pattern of lines and relative light and dark spots that initiates the same sequence of firing which would lead to the same end result—activation of the cells responsible for identifying the face of that individual. However, the speed at which we are able to accomplish this place such serial processing into question. Perhaps more relevant to the present discussion is the question of how the products of lateral inhibition, namely lines and edges, come together to compose images so smoothly? Would an insult to the brain site responsible for this task result in reading/visual processing disorders?

While I was thinking about our difficulties seeing at night because of the lack of cones at the fovea, I began wondering about how night-vision goggles work. I think that they are based on contrasts (so that you can see outlines of objects). How exactly does that work?

And about the tree falling in the woods . . . We said that color is a function of the brain and not a physical reality. Then we are said that sound is only a physical reality when there is an apparatus to interpret sound waves (an ear). So is light (and not just color) itself not a reality if there is no eye for it to enter? This is hard for me to understand. Is something only “real” if our I function is aware of it? For example, if we have an X-ray, there are X-rays travelling through our body, even though we are not aware of them (ie, we cannot sense them moving through our bodies). Does that mean they are not “real”?

To clarify the question of the falling tree, I had discussed the issue with a philosophy major. Philosophically, there is no true answer to the question, "If a tree falls in a forest and no one is around, does it make a sound?". A constructionist believes that individual perception is reality. In order to perceive that the tree made a sound, the individual has to have experienced the sound at the moment the tree had fallen. Contrarily, a realist believes that the acknowledgement of a falling tree making a sound is reality. The fact that sound waves are produced as the tree hits the ground and our experience of knowing that a falling tree creates sound sufficiently explains that there falling tree produces sound. What if a tree falls next to a deaf person? Would he/she hear the falling tree since he/she could at least feel the tree falling?

Sound by definition is heard. Thus, I am not sure what I believe but the ideas are definitely fascinating to me.

The answer could be very philosophical indeed. As we have learned in empiricist texts, we believe that the sound would continue without our presence because we have this feeling of EXPECTATION due to our past observances. We walk out of a room with the radio on, and enter 10 minutes later, expecting the radio to still be playing sounds. This is only because we must believe in the continuity of things, in order to make much sense of the world and to make the world seem less random. It all comes down to pyschology and how our brain functions. It always comes back to the brain.

So, in regards to the tree falling in the forest: my take on the situation is that when no one is there, the tree does not fall at all. There is no tree. Reality is perception, without that, nothing exists to us.

I'm way out on a limb here. I am prepared for the limb to break and the tree to fall.

Somebody else suggested that this tree is perhaps of little consequence if we are not actively perceiving its activity. Why have this headache over rustling branches if they are not crashing through our living room windows? But don't things happen every day, every minute, that affect us without the immediacy of direct perception? And it still seems strange to claim that people determine reality in any manner that could be deemed objective. The only solution I can see right now is to allow for several different planes of "reality," some of which depend on an organism's sense as an mediating variable.

I think the topic of the tree falling in the woods is extremely interesting. And I'm not sure which side I lean towards. However, the example of a deaf friend being with you and how that could skew our answers is hard to see... because actually, the deaf friend has other ways of perceiving it as falling (sight, the wind brushing against him/her when it fell, etc.) However, I'd like to draw another parallel.

in the middle of class, we talked about how there are portions of the world that we don't percieve because we don't have cells to perceive them. Well, there has always been the debate of paranormal phenomenon. What if some people have the senses, to see and hear things like that. Most of us don't, and we consider ghost stories (etc.) to be totally untrue. Could this be simply another version of the tree in the forest? What if we don't know of this whole other layer of reality. We already debate whether its real or not... same thing.

That was just a weird parallel that came to me. Just a thought.

What is really interesting to me is the idea that reality is in a sense now, completely subjective. If reality as I know it is only my brain's interpretation of reality, then this leads to some interesting questions about things like, I dunno, drugs. We've all heard stoned people say that they experience reality differently while they're high. Is their reality not real simply because it is caused by a reaction of their brains to the drug? I mean, everybody's brain functions differently anyway right? What is percieved as reality by my brain when it functions normally is very different than that which is percieved on a normal basis by say an autistic person, or a blind person, or a person who routinely suffers from hallucinations, or someone under the influence of drugs. Who's to say that my brain got it better than the autistic kid's or the blind person's or the stoner's? I know I'm probably wrong here, but it's possible then to think that a reality experienced under the influence of drugs may be no less valid (no more off from the truth) than the "reality" we experience every day.

Even though lateral inhibition of our visual system making reality defined by the edges, it doesn't mean that this view is wrong or skewed. Our brain is capable of taking these factors into account and matching them up with reality. Lateral inhibition shows that the nervous system has a certain set of assumptions it works with. But, the example of the glasses shows that this is elastic if the nature of 'reality' changes.

The notion of a tree falling in a forest with no one around is really a question about the nature of perception. Is sound really only defined by some hearing it? Is it just sound waves then? It depends on the definition of those terms. Yes, what each person hears may be interpreted slightly differently, but the basic cause is still the same reality. And, if the sound heard does not correlate to reality then your nervous system corrects for it or it shows up as a defect. I'm not sure if I accept the definition of things like sound and color as subjective to our individual biases dependent on our perception. These things exist outside us, and our convention of referring to them doesn't mean that is the only way they exist. If the word 'dog' had no reality associated with it then dog would have no meaning. Thus, dog is tied with reality, just as our associations are. Calling them our associations does not make the reality any different without the name.

A similar thought experiment I have heard is, imagine there is someone who sees every color as its opposite--that is, green as red, yellow as blue (are those opposites?), etc. She has learned to call the grass "green" even though she sees the color the rest of us think of as red, because for her red has always been called "green." So the question is, would she have any way of knowing the difference or having it explained to her? Would we? Is it possible that half of us really see green as red? Does it matter? An interesting idea, i think....

Hmmm...i'm still churning that idea in my mind, wondering what other conclusions this will lead me to

To me the answer is yes---somehow, I feel that it would be entirely too self-centered of a view to be of the opinion that the tree waits to fall until just before I approach it to sense its falling. I know that this statement sounds a little extreme, but how else can you explain my perception of the a tree that has fallen that has been upright the last time I had seen it? Obviously, I must think to myself that something must have occurred between my two viewings of the tree to have caused it to fall-- does that mean that I think that it only happened at the point wheen I could perceive it?? NO. It could have happened anytime. Along with this conclusion comes the implication that it is possible for "stimuli" such as light, sound, smell, etc. to occur with or without the presence of a human being to receive them.

Maybe I'm way off here, but it seems relatively logical to me....

With bilateral damage not only is the person now void of perceiving colors but also unable to remember or imagine colors. The memory of colors is gone. The experience of color is no longer a part of the "I" function, the consciousness.

This leads me to think of the "I" function as--not only a box but something with tentacles throughout the nervous system.

What if this were particularly true for sound (since it's so variable). What if people don't hear the actual same thing as everyone else heres. We would Think that we do, but we'd never really know. Perhaps this is why some sounds are totally unpleasant to some individuals and peaceful to others. Perhaps its not taste, just science.

Say then that the tree falls, and it causes air compressions (and anything else we might not be aware of), sends some kind of signal. The observer walks by, his/her capacity to perceive is able to pick up part of this signal and interpret it, and s/he calls it 'sound.'

Then, what about this one? Yes, the tree makes a 'sound' as it falls, but it really makes so much more because who knows what else is in that signal. If the point in Flatland observes another 'point'which is really a line, then if the observing point is not there to observe the 'point,' the 'point' becomes a line. So there's an argument that the tree doesn't make a 'sound' when without the observer.

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