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Neurobiology and Behavior, Week 10

Paul Grobstein's picture

Welcome to the on-line forum associated with the Biology 202 at Bryn Mawr College. Its a way to keep conversations going between course meetings, and to do so in a way that makes our conversations available to other who may in turn have interesting thoughts to contribute to them. Leave whatever thoughts in progress you think might be useful to others, see what other people are thinking, and add thoughts that that in turn generates in you.

As always, you're free to write about whatever thoughts you add this week. But if you need something to get you going, we've started looking at the nervous system from the input side, discovered again that perception is not independent of output (eye movements, focus control) and that what we see is an "informed guess" about what's out there.  Thoughts about either or both of those sets of observations/conclusions?

aybala50's picture

seeing vs. perceiving

When something is reflected on the retina, the image that appears there is not the image that we perceive in our brain. This got me thinking about perception in general. I already knew that perception is a complicated process for humans that requires a lot of work on the brain's part. What determines how human's perceive things differently? Is it experience? Some kind of difference in the brain? 
drichard's picture

My questions deal with the

My questions deal with the idea of pattern continuation and the brain's ability to construct. We know that we have a blind spot. We know that the brain fills in this blind spot with outputs rather than inputs. It seems that our "perception" of reality is informed by the brain enough to call it a function of the brain. It seems that Dickinson is winning the argument. What does this mean for humanity that we realize that "perception" is a very individual, even subjective phenomenon? What does it mean for science? Science, as we have defined it, is a summary of observations constantly informing itself through new observations. What does it mean that these observations are subjective? What if a variety of constructions can fill one blind spot? Which one is correct? It seems that developments in neurobiology may be problematic to science as something sterile and calculable.
Paul Grobstein's picture

Science exposing science

Would it be a bad thing for science to be revealed as something other than "sterile and calculable"?  For science?  For humanity? See The Brain as a Learner/Inquirer/Creator
nafisam's picture

I also found the McGurk

I also found the McGurk effect to be a great example of how our senses are interconnected and interdependent on one another. It definitely has changed my thoughts about our senses, and shows that they are not compartmentalized into separate areas. However there are still gaps in my understanding of how senses influence each other. For example, when one has stuffed up nose, and can't smell anything, one's sense of taste is also diminished. However I have heard that blind individuals can experience a heightening of the senses. I am curious to know if blind individuals, or individuals missing one sense for an extended period of time, actually experience a heightening of senses, or if they learn how to use the other senses more effectively. How does the nervous system control these adjustments?
hlee01's picture

week 10

Retina is a thin layer of tissues with bunch of neuroreceptors that send messages to the brain. Light goes in through the pupil and is absorbed by retina. Therefore, the pupil is black becaue no light comes out. However, when too much light is given off, light is reflected back out of the pupil. Considering all of this, why is there a tendency for people with lighter-colored eyes tend to give off light more often than people with darker-colored eyes? Also, why can people with lighter-colored eyes see better in the dark?

In another note, I think one of the reasons why the picture in our heads doesn't match up with the real picture has to do with saving energy and putting that saved energy to better use for survival.

bpyenson's picture

Teliological View of the Brain's Perception

Although I was really fascinated by the lectures about perception/vision last week, I was most intrigued by the statements on evolution of perception.

In particular, I was intrigued by the lateral inhibition network of perception that stated that what we perceive (by sensory neurons) is quite different than the unconscious construction our brain puts forth to understand the inputs.  When in development does this filtering and construction by the brain develop?  How does this relate to perception development in similar organisms?

Also, it seems that with this notion of brain evolution, one tends to think of the human brain as the most advanced/complex.  Although evidence from the neocortex would suggest this (see my first paper), perhaps perception does not?  Could it be that other 'less complex' organisms in fact have more complex perception systems?  How should we evaluate which species has the most advanced/complex visual/perception system?

BeccaB-C's picture

I want to address your

I want to address your query about when the brain begins to make constructions and adjustments to sensory visual information, and to question it further. Critical periods exist for the development of many cognitive and neural behaviors.

Landmark research examined newborn kittens, placed in environments which limited their experience to a few of many visual elements, and examined their sensitivity to visual elements that were not within their environments until a certain point in development ( It turns out that critical periods exist for many aspects of vision, which leads me to consider the constructions of the mind (and adjustments in what is physically recieved by sensory systems of the brain, prior to a signal's travel to BA V4 (the visual system in the occipital lobe).

It is clear from the kitten research that it is physically possible to recieve horizontal input and not produce any sort of "horizontal output" in the form of conscious awareness/perception of horizontal line. How, then, do these constructions, such as the perception of horizontal lines, manifest themselves in terms of critical periods for more holistic processing? What about squares? They include horizontal lines--are they percieved once the critical period has passed without recieving input? Does the brain fill them in despite never having experienced them (in which case the plastic areas of the brain which recieve input and produce output for horizontal lines may not yet have atrophied)?

ddl's picture

Visual 'Blind Spots'

Last week in class, we discussed how there are “blind spots” in our vision that need to be filled by the brain speculating and then projecting what it thinks should be perceived in those areas.  This raised the question for me of why evolutionarily human beings have developed these blind spots?  It seems pretty apparent that it would make more sense to have developed a means of visually perceiving the outside world in which no blind spots are found.  So then why is it the case that such spots exist?
Percival52's picture

Behavior and Senses

Earlier in the week we breifly mentioned the possibility that someone's behavior isn't necessarily voluntary. To me this means that someone placed into a particular situation will react in the way that is most natural and fluid. However we all know that this is not the case because we have all showed restraint in various situations. The difference to how we may behave may be to due to the invovlement of the I function. The I function may regulate how our behavior is expressed but just like when we are dieting using the I function to supress out hunger, the I function can't outlast the set point. This is probably the case when someone says they just "snapped". The couldn't control themselves anymore, the I function was exhausted and couldn't contain the behavior that was most natural to them at that time. Since the I function learns through reafferent loops and our senses, when someone goes "crazy" does that mean that the I function is no longer working. We established that we have more then 5 senses and all inform each other equally behaving as a check and balance system. Does that mean we should be able to talk someone out of their "crazyness" by reminding them of their other senses, to convince them what is real and what is not?
Olufemi.Nazsira's picture

Visualizing sans Photo Receptors

Quickly, this notion that the brain constructs images independent of the I-Function brings a whole new meaning to the saying "Caught red handed" and "I saw it with my own two eyes."   On another note, Recently I was having dinner with a friend and he began telling me about "The Secret: The Law of Attraction." Essentially the premise of this theory is that in life you can have whatever you want: if you call out to the universe, it, in due time, will respond-it always does, every single time. Now one of the key properties is visualization. In order to make the call out to the universe to get this desire fulfilled, one must visualize and truly see in their minds what it is that they want and focus intently on that. As I am still rather unfamiliar with this theory, I wonder just how much it aligns with or relates to our most recent class discussion about images being constructions of the brain? I mean clearly these visualizations do in fact involve the I-Function as they are intentional and premeditated, but how does the nervous system's own conjuring function, especially as this is a matter of seeing without literally using the eye of its photo receptors? For instance, I suppose that if one decides s/he wants Mr./Mrs. Right to come along, s/he must visualize a person whose face they know nothing of, in which case I imagine the brain kicks in to fill in the gaps. This is tricky because it's often easier to list the qualities and characteristics in a mate as opposed to physical features, but I imagine that it that would be precisely the area that there nervous system would be concerned with.

Bo-Rin Kim's picture

filling in gaps and edges

I remember learning in previous biopsych classes that our eyes do not fully perceive the visual world and that our brains "fill in the gaps" to give us the picture that we "see" when we look at the world. This concept of "filling in the gaps" has always been mind-boggling to me as it is so fascinating how all humans seem to fill in the gaps in the exact same way. We learned in class that our brains picks up information about edges and is able to fill in what goes between those edges. I believe it is the ganglion cells that are responsible for this ability as they are able to compare a particular visual point to its surroundings. However, in one of the blind spot tests that we did where our brains "filled in" a yellow dot that was in our blind spot with a red dot (the yellow dot was surrounded by other red dots), it seems as if the brain not only fills in edges but is also able to create edges. This concept is interesting because it shows that our brains don't just simple "fill in" gaps but can create new boundaries within those gaps. So how does our brain do this? How does it know where to create new edges and not just fill in the existing ones?

Moreover, I understand that each of our eyes has a blind spot where the optic nerve endings are. But, in all of the blind spot tests that we did, we had to close one eye to get the "blind spot effect". So doesn't one eye see what is in the blind spot of the other eye (as each eye's blind spot is in a different location, creating a complete visual picture that doesn't need any mental "filling in"? I believe this question was raised during class, but I forgot how it was addressed. Since most people can see with both eyes, when is this mental filling in of the visual picture necessary? 

redmink's picture


I am interested in the organ, eye.  And I am so glad that we talk about vision and its relationship with out brain.  Last week, I was surprised to know how our brain only recognizes the edge of the object and fills the blind spot with continous pattern.  I agree with Leah's notion that the reason why we humans go for only the edge is that otherwise, it would be too much information for us. 

To add onto that, I think our brain is very busy with relating the newly accepted information with many other things.  To make an analogy, we earlier learned that out of the three types of neurons(sensory, inter, and motor), inter neurons takes up the most part of our nervous system.  In the case of the edge and the brain, if our brain was to get all the information including the gaps within the edge, it would reduce its ability to think, interpret, and proceed.  In other words, we would be too overwhelmed and would lose our autonomy. 

So, i think it's for our benefit in which with the minimal amount of information that we need to get, we fully utilize it to connect with other stuffs such as making plan for the future, reflecting on the past experience, and creating curiosity about the object even further. 

I think most of the human history is made within our brain by great thoughts or interpretation, not by the actual facts or objects that are out there.  I think such leeway to differentiate or personalize the objectivity of the world makes this world more diverse, creative, unexpected, and beautiful. 

That's why there are great pianists, or other artists who play the song written by a single composer in their own ways with different emotions, etc. I like how our brain is always like a factory to create various stuffs based on the minimal information given.  Credit for interneurons.

I further want to know more about what and where in our body actually controls how much information we should receive. 

I also want to know if there is any disease in which a person cannot control the reception of limited information we need.  What if the brain fails to see only the edge.. is there such a disease?

ilja's picture

mysteries remain

We learned that the brain makes informed guesses (it makes up things), and that it uses many different structures and factors (past experiences, output, inputs, environment etc.) in order to interpret the world around us. I find it interesting that as I’m starting to understand the brain better, and its function as well as the link to behavior, the mysteries of the brain is not decreasing. There are still many questions left, many gaps, many problems in explaining our behavior. It seems like the actual answers will never be there, not only because of the summary of observation model that we use but also because of the brain itself. We can never know which of the many many factors influencing our behavior was most important, we can know which parts of the brain were important but we cannot account for everything. Knowledge about the brain will help us understand each individual better (make an informed guess about the brain) but it seems like we will never be able to fully explain everything.  

jwiltsee's picture

Dreams-predicting the future

This week in class we learned our vision and hearing depends on a combination of inputs other than just our eyes or our ears.  And that we can sometime "sense" when things are going to happen without a direct stimuli.  I'm trying to make a connection here to dreams in which in the future you think to yourself that you had dreamed that a certain situation would occur.  Is the mind able to create dreams that predict the future?  Since the mind is able to "sense" things, is it able to sense the future without any direct inputs of what the future has in store?  And then how is it able to piece together images that your have never seen before to create the future situation in the present? 

Sam Beebout's picture

I have been trying to

I have been trying to connect the edges metaphor to other sensory perceptions. Since its all about difference, its easy to see how it applies. The things we "feel" are only the things we are made aware of. We are never tuned into how our entire body is feeling. Similarly, with taste and smell we are probably differentiating between the basics (sour, sweet, bitter) and filling in a lot of it.

Thinking about taste and smell added another layer to our conversation about filling in things we see. I started to think about how smell is the strongest taste tied to memory. A significant part of the "filling in" process must also have to do with memory. When I ate chocolate cake tonight, I was expecting it to taste a certain way. 

It got me thinking more about a quote I heard that we only ever see something once. The same thing must be true for our other sensory perceptions. The first piece of chocolate cake I ate has probably influenced every other piece of chocolate cake since. I am probably filling in more from memory than what I am actually tasting at that moment.

Sarah Tabi's picture

Are we making the same "informed guess"?

Since what we see may be an "informed guess", does that signify that human beings in general are making the same guess in their minds?  In our blind spots, all of our brains make up for what's not there.  We all agree on what a particular color looks like (e.g. yellow is bright, black is dark).  Humans definitely perceive their surroundings differently than a cat or a snake.  So are we basically saying that since we have the same equipment, we are making the same "informed guess"? 
Lisa B.'s picture

Week 10

I thought that the best demonstration of speech perception was the McGurk effect.  Is he saying "ba ba" or "da da"? During the YouTube demonstration I heard "ba ba" when my eyes were closed and "da da" when they were not closed. This was exactly what McGurk and MacDonald described in their paper, that hearing and vision involved more than one sensory modality. Furthermore, now that I know that senses function from the brain and not body I am better able to understand other topics in neurobiology. For example, dreams are a construction of the brain and may be a combination of more than one sensory modality. Also, I would like to further explore our social sense in relation to the construction of the brain. 
BMCsoccer01's picture

Something that Catches the Eye

I agree with Crystal in that many things (objects, people, etc.) that people "see" are constructions of the brain. And, I'm sure we can all relate to the expereince of sitting up in your dorm room doing homework and while reading, something catches your attention out of the corner of your eye. You could swear that something was either in the corner or ran across the floor. Now, whether your first reaction is: "oh god, please don't be a mouse! or hmmmm, that's interesting," is irrelevant. The interesting thing about hallucinations & things catching one's eye is how does one's brain know that the object/thing/person is not really there?

We have all heard the expression: "it's your mind playing tricks on you." But, where do these tricks come from & why does the brain allow one's eyes to do this? There is a big difference between thinking that you saw something & "knowing" that you actually did in fact see something, so how does the brain differentiate, if it does?


Leah Bonnell's picture

Why edges?

During class I wondered by human vision would evolve to process by edges. Initially, this seemed liked a pretty arbitrary method with the possibility of error or the brain misleading you. The idea of the brain filling in gaps does make me a little nervous. People usually think of what we see as fact, when a lot of it is made up by the brain. 

But for why we evolved to see by edges, I think this method is the simplest. If we had to process everything we saw, I feel like it would be too much information. In class we mentioned that edges are important to understanding biology. In terms are learning, we look at the edges to see how things are different. For example, if we were studying biomes are wanted to know were different biomes were, we would only look at the edges. The same method hold true for vision; we only need the edges.  

bbaum's picture

I still can’t rap my mind

I still can’t rap my mind around the fact that the onlything that we don’t actually see the objects in the world, but we only see theedges of objects. I had never thought about the world as simply changes in theintensity of light, but if I think about it now, it makes a lot of sense.


I also find it interesting that the brain is able to convert2-D images on the retina into the 3-D images that we perceive in our minds. Idon’t understand what process is going on and where this process is occurringthat is allowing the switch in dimensions. Is the image that is broadcastedonto the retina the image that is sent to the parts of the brain that deal withvision and then converted, or does this process occur in another area? Could itbe possible that the area of the brain that is involved with converting the 2-Dimage to the 3-D image is also connected to our sense of touch? We are able totouch and explore objects and understand that they do not exist in 2-D, so ourvisual cortex and the areas of the brain involved with touch communicate tocreate a more realistic picture of the world. If this is true, it would beinteresting to understand how newborns actually see the world without knowinghow the world is supposed to look.


Another interesting topic related to vision is blindsight.Blindsight occurs when an individual is able to recognize objects even if theyare unable to receive visual signals in a certain area. For instance, a man maynot be able to see anything in his right field of vision, but if a greencolored object is held on his right side, he will still be able to correctlyidentify the color of the object. To me, this phenomenon seems to be related tothe existence of the blind spot that all humans have. It may be possible thatthe brain is simply filling in the parts of the visual field that the man isunable to see because of damage to his eye, optic nerve, etc. Blindsight maywork by the same mechanisms that control the blind spot, only on a largerscale.


hamsterjacky's picture


This may take a philosophical turn to what we are learning, but what is perception? Yes, they are inputs to our brains which gives us an idea of what out environment is. But why is it that we are taught some certain things, such as colors. Why is red, red and not green instead? Why have we been taught what some things are. And how can one define pain? I've learned that it is just action potentials traveling at a hig frequency which causes unease, but why does out body react certain ways? is it that evolution favored it? Such as, when we are in pain, why do we scream sometimes but at other instances?

For example, let us consider severely sore muscles. Sometimes a massafe helps but it hurts during the process. At the same time, it feels good - some people describe this is a "sweet" pain. is this because the body instinctively knows that although it hurts now, later on it will feel much, much better?

I know, a lot of questions - but isn't that the point?

SandraGandarez's picture

Today in class we discussed

Today in class we discussed that there are many differences between the picture reflected on the retina and the picture we have in our heads. I think this is odd just because when you think you are seeing something, it becomes a quickly altering image before it is transferred to you mind. This brings to question how everyone perceives images they view, or even how the image can be changed/ distorted by the time it reaches our conscious thought. Is this the same reason peoples eyes play tricks on them? Like if I am thinking of someone and I think I see them is this because picturing them in my mind gets mixed up with visualizing them at that moment. Just like many times my mother swears that she saw her keys on the table, is it because she has seen them there before and that becomes confused with current images? How exactly do mental images and physical images differ in our nervous system functions?
jlustick's picture

Vision, Dreaming, Hallucination

I'm wondering how our discussion of vision this week relates to dreams. We talked about how what we see is made up in part by our brains; our brain essentially fills in the gaps to make up for the holes in our vision. Vision in dreams is entirely a product of our brains, given that we are not receiving any visual input. Is the part of the brain that pieces together images in dreams the same part that fills in the gaps when we are awake? Do the visions in dreams have to come from somewhere? Is each image buried somewhere in our memory bank? For example, maybe an unfamiliar face in a dream is one that we saw in a magazine photo or television commercial long ago. Can the brain actually formulate new images and how might this affect our conception of visual art?

I am also curious as to whether the part of the brain responsible for images in dreams is the same as that which produces hallucinations. What is the real difference between the two? Is it simply being asleep versus awake? In other words, is dreaming simply hallucinating while sleeping? Why do must people not hallucinate?

eglaser's picture

Seeing color

When thinking of seeing I first think of color rather then shape in my environment. I was surprised to learn that color vision came relatively late in our evolutionary tieline. We had grasping hands and forward facing eyes before we had the ability to see in color. No one is entirely certain why we developed the ability to see in color, some think that it aids in depth perception, others think that it was a way to distinguish between fruit that is underdeveloped and ripe. One professor even hazarded the guess that it had something to do with flowers.

In any event we still see primarily in line and black and white, we notice the outline of things first then fill in the colors in a somewhat haphazard fashion. what does color ad to our world now? What would it be like to be color blind or to have never developed the ability to see color in the first place? How does color change the way we feel, think and interact with our environment?

jrlewis's picture

remembering my biochemistry...

The biochemistry of eyes and vision is primary signal transduction, the process of converting information from receptors into chemical change in the cell.  Light is focused by the lens onto the retina.  Rods and cone are the photosensory neurons that form synapses with interconnecting neurons in the eyes.  Then the signals from many neurons are integrated by the ganglion neurons and later transmitted to the optic nerve. 

Light causes a cascade of chemical reactions that result in the hyperpolarization of the cell.  When light interacts with the rods and cones, 11-cis-retinal, a component of the integral protein rhodopsin, is converted into all trans retinal.  This induces a change in the conformation of rhodopsin and results in rhodopsin catalyzing the replacement of GDP to GTP bound to the protein transducin.  The protein transducin dissociates into two subunits, one bound to GTP, the other bound to two molecules of GDP.  The complex of transducin bound to GTP activates the cGMP phosphodiesterase enzyme (PDE).  PDE changes biologically active cGMP to biologically inactive 5’-GMP; this causes a massive decrease in the concentration of cGMP.  As a result of the low concentration of cGMP, the cGMP-gated ion channels close and the cell becomes hyperpolarized. 

The process by which the cell returns to the resting potential is also interesting.  Remember the transducin protein? It hydrolyzes its bound GTP to GDP and reassociates with its other subunit.  This causes the inhibitory subunit of PDE to bind and deactivate it.  The concentration of calcium ions in the cell is low enough to allow guanylyl cyclase to synthesize cGMP.  When the concentration of cGMP is high enough, the ion channels will open, sodium ions will enter, and the cell will return to its resting potential. 

There are several properties of this process that are relevant to our study of the sense of sight.  Signal transduction significantly amplifies the original signal.  According to my biochemistry textbook (Lehninger Principles of Biochemistry), one photon of light closes about 1000 ion channels and changes the cell’s membrane potential by 1 mV.  It is also important to recognize the time scale for this process, it takes time on the order of seconds to minutes to prepare rhodopsin for excitation again.  All the trans-retinal in the rhodopsin molecule must be replaced with 11-cis-retinal.  While there are a lot of biochemical details to get lost in, it is important to remember the end result; information is transferred from photosensory neurons to other neurons to the brain by electrochemical changes in cell membrane polarity.  

Brie Stark's picture

When we were discussing is

When we were discussing is the idea that the senses give our mind a picture, either a visual picture, an auditory picture, or one made up of information from other senses, like olfactory, taste, or tactile.   Your mind doesn’t have its own private pair of eyes, however. Therefore, the mind can’t be looking at the "picture" that the senses give.   So, it’s that all of our perception is driven/colored/guided by our own interests, needs, aims, and sometimes even biases--which is why we all perceive different things.

I wonder, then--and I'm not very educated in this subject at all--how this could be applied to things such as the No Child Left Behind Act, where every student is held to a new, higher level of accountability.  Isn't the perception of our brains, which is so different and varies from individual to individual, a bit contradictory to the entire purpose of this act?  It seems to me that education would fare better if it took into account the difference of perception that we learned from regarding how vision and brain work together.

Crystal Leonard's picture

ghosts - constructions of the mind

Many things that people "see" are really constructions of the brain. This idea got me thinking about ghosts. I personally don't believe in ghosts. However, several people that I know, including my sister and my aunt have "seen" ghosts. I know that they aren't lying; they truly believe they have seen/heard/spoken to ghosts. In my opinion these experiences are constructions of their brains, similar to a hallucination. My question is then can a perfectly healthy individual's brain repetedly construct a very specific event out of nothing? And if so, why?