Final Blog Entry

 

 

 

 

The real world vs. the perceptual world; in which do we want to reside?

 

            One of the things I found enlightening and at times surprising about this perception class was that most of what we experience is in fact not really what is out there in the real world.  This was shocking to me simply because of the heavy emphasis we currently give sensual experiences.  We use these senses for diagnosing patients, judging the edibility of food items, making life or death decisions and much more, when in fact we are only working with a very limited snapshot of what is really out in the world.  Although the other senses have their own faults, I would like to focus on vision just because it is one of the senses we mainly rely on.

            Vision is by far the most relied on of all the senses because it tells us so much about our environment and allows us to interact effectively with said surroundings. Ernst & Bülthoff (2004) would argue that all senses are of equal importance to our perceptual experience noting that the information from one sense organ is not reliable enough and we must integrate the information coming from all the sense organs to get a clearer picture of the world.  However, they also note that if for some reason integration is not complete then the information we perceive falls prey to illusions like that of the Necker cube mentioned in their paper as well as other misidentifications.  In these examples they clearly use vision to show their point virtually noting the importance of vision in relation to all the other senses.   Nevertheless the point of this blog is not to prove which of the senses is more important, but rather to show the faults of one of the most relied upon of the senses.

            Visual perception is an alteration of what we should see visually due to the accommodation our brain makes so as not to be overloaded with too much information.  Ernst & Bülthoff (2004) give a good example when they mention the illusion one experiences when sitting on a train and the ambiguous information from another train across the tracks gives the illusion that one is moving when in fact it is the other train that is in motion.  Synesthesia is another support for the case of living in a perceptual world.  This is because this particular condition deals with a certain aspect of vision that is exclusively left for the visual sense and the perceptual world.  This of course is color perception.  Color as mentioned by a previous post is a perceptual factor in that all kinds of light including pure ones[1]have no color in them but simply wavelengths that we assign different colors to.  This means the very colorful world that we see is all an alteration of the real world that has been changed by our visual system.  Moreover, the world we see is probably not the same world another person might see because the wavelength set for them to think of the color green may be very different from the one we use for the same color.  All this coupled with the fact that various conditions like the background or the luminance of an object can change the perceived color (say change yellow to green when the wavelength being received is one we usually use for green) is more evident of the fact that we live in a perceptual world—at least visually.  

                To conclude I again would like to bring up the condition synesthesia just because it really is fascinating.  Ramachandran & Hubbard (2001) try to expose some of the false beliefs about synesthetes noting the subconscious experience of synesthesia, and that the condition seems to runs in families.  They also mentioned something really interesting that caught my attention. This was that synesthetes are able to identify letters or numbers when shown on the periphery due to its characteristic color.  They are unable to see the letter or number but make a guess (that is usually correct) because of its color.  “I can’t see that middle letter but it must be an “O” because it looks blue.” (Ramachandran & Hubbard, 2001)  This highlights the fact that a condition that seems so real and vivid to these individuals must be another perceptual trick.  There are no cones in the periphery so there should be no color information, but yet that is not the case.  Or perhaps cones and rods do not really matter and we have just used them as an explanation as to why we hardly see any color in the dark or in the periphery.  Who really knows enough to tell us what is real and what is perceptual.  Do we live in the perceptual or real world?  Well I say perceptual, because that is the one I live in, I could not tell you a thing about what the real world looks like.

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[1] Pure light is sunlight passed through a prism and then filters to only have one wavelength that we may call pure blue light, or red light e.t.c.

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Response to what is the aperture problem?

The aperture problem arises from the limited scope of view that each neuron in the visual system has when looking at the entire visual field.  Similar to how the each eye has a limited view of the entire visual field, the individual neurons also have a limited view of the entire visual field.  Additionally, all these neurons do not respond to motion the exact same way.  Some neuron respond to vertical motion while others to horizontal motion and in many cases all these directional selective (DS) neurons are right next to each other. In the case of the aperture problem we see through an object moving through a small window or aperture that represents a cluster of receptive fields ( see Figure) in the visual system.  What happens then is if an object then begins to move in this aperture the actual direction of the object becomes ambiguous.  So for instance if in this small window we perceive an object to be moving to the left the object could actually be moving up-ward diagonally left, straight left or down-ward diagonally left.  All these would be perceived as left because the entire picture of the object is not shown through this aperture. (Click for a demo, can you tell with 100% accuracy which direction the object in the aperture is moving).

            This phenomenon sheds some light as to the amount of guess work that our senses have to make about the events that occur in the world.  Far from all the information that is in the environment gets to the cortex (photoreceptor and ganglion ratio) and even the information that does get to cortex could be interpreted inaccurately depending on the position of neurons and their directional selectivity.

Response to question; what does the condition of synesthesia tell us about “normal” sensory processing? What do you imagine it is like to have this condition?

 

Well one of the interesting things about our visual system, and all our other senses for that matter, is that our perceptual experience do not always correlate with what is in the environment.  After Newton’s prism experiment, it has become wildly known that most objects do not have particular colors and that the colors we perceive stems mostly from our internal systems.  In this case an apple is not really red but a mixture of lightness contrast that results in a particular hue (to us) when in the presence of light.  What this all means is that the perception of color is heavily determined not by the outside environment (which is really all ‘white’ composite light) but by the internal sense system (that pick up the reflection of particular wavelengths and translate these wavelength into specific colors).  This may seem really strange to most people but the presence of synesthetes gives credibility to this position.

            A synesthete can read the above words and see different colors (see above Fig) for each letter or particular words.  If color was heavily based on the outside world then this phenomenon would be impossible.  Simply because words that were not colored could not suddenly have color appearance.  Color is then a very internal experience that has us converting white light into different wavelengths which we in turn describe as different colors.

            I would imagine that having this condition would make things confusing at first but I think it would eventually get pretty fun.  I mean one of the things I really liked was the ability to tell pain by color that was described by a synesthete, Carol.  If this ability was applied to all different emotions then it would surly make my days more interesting; as I would be able to tell when I am angry (red I suspect) or jealous (green) or even in love (would this be red again…I wonder?).  I imagine it would also open up a whole new way of perceptual experience that is rich and vibrant and more interesting than that of the normal perceptual experience.  I wrote in one of my earlier blogs on the experience of the smell sense being heightened, and the increased perception of colors that came with the episode.  I also speculated that this person was experiencing a fuller world than most experience.  In the case of a synesthete they experience the world using an more of their sensory and perceptual powers (than most).  I wonder then what would happen if a synesthete were to be exposed to a world where smell also heightened their color perception…would it be a nightmare of flooded information or a truly enlightened state?  

Response to: What is cortical magnification and is it a good or bad thing?

          Cortical magnification refers to the disproportionate number of neurons located in the visual cortex that are reserved for high acuity fovea vision.  In other words most of the visual cortex is reserved for the fovea while only significantly lesser portion is reserved for peripheral vision.  This is a strange occurrence because there are more photoreceptor cells and ganglion projection for the periphery.  The reason this occurs is because the fovea is responsible for high acuity vision and the cells pay more attention to this particular type of vision to ensure objects seen with the fovea are perceived with the greatest clarity.  Furthermore, with the ability of the superior colliculus to orient eye movement towards novel stimulus the chances of information falling on the fovea are greatly increased.  The periphery is not paid that much attention because all it needs to do is detect a stimulus and alert the superior colliculus to turn the eyes towards the novel stimulus.

            With all the information above it would seem that having this cortical magnification is a great phenomenon but I believe it can also be a bad thing depending on who you are and what’s important to you.  Take for example a caterpillar. (see Fig)  The caterpillar does not have just two eyes like many mammals instead it has an array of light sensitive receptors lined around its sides that it uses to see.  An organism like this has no need for cortical magnification, and if it did, the reverse would probably be more beneficial.  The caterpillar needs to be able to see all around it to efficiently notice if a predator is approaching so it can run away.  High acuity would be useless because as the caterpillar cannot very well turn its head to the new stimulus, it may not be able to clearly see an attack until it is too late.  With superb peripheral vision the caterpillar would be able to notice any predator coming regardless of what side the attack was coming from and solely with that information be able to make the necessary response.                 

Response to: What is an OFF-center ganglion cell receptive field (GCRF)? Why is it organized they way it is?

The first time I heard about the on-center, off-surround, on-surround, off-center phenomenon I have to admit I was completely lost and it took me awhile to finally grasp the concept.  Unfortunately, however, it seems I still do not understand it fully because I often shy away from question regarding this particular topic.  Well I have decided to face my fears and try to answer the ganglion cell receptive field topic for this week’s post.  For the sake of the examples I am going to be using, I will be talking about both on-center and off-center.

  The on- center GCRF consist of a cluster of ganglion cells that are arranged in a pattern where a particular spot in the middle of the cluster of cells is receptive to light and depolarizes, hence causing more action potential, to its connected neurons (see Fig 1a).  This is the same phenomena that is present in the off- center GCRF except reversed.  So in this case the clusters of cells are seen once again to have a region in the center and a complementary surrounding region. However, unlike the on center, the off-center is receptive to light only on the surrounding cells (see figure 1e).

            Furthermore, the surround of the on-center and the center of the off-center have unique qualities of their own in that they are receptive to non-light (or dark).  In the case of the off center, when the surround is stimulated by light the cells will fire action potentials at its highest frequency.  Additionally, if the center of the same off-center has non-light the cells will also fire at their highest frequency.  So a fully activated GCRF for an off-center cell will have both the surround stimulated by light and the center stimulated by non-light (or darkness) (This can be seen in both figure 1e).  

            The second part of the question that asks why the ganglion receptive fields are organized this way can be answered by first looking at Hermann’s grid.  The bizarre effect seen where the space between the squares seem gray but turn back white when looking directly at them can be explained by the phenomenon called lateral inhibition.  In this case (still using the off-center situation) the portions of light and non-light all fall on both the center and surround of the GCRF.  This competition between the activation of the off center, by light on the surround and non-light on the center, may seem counter productive but provide cells with an easy but highly selective way of detecting stimulus, (either light or dark or both) and allows them to respond efficiently and accurately to that stimulus, by corresponding action potentials.  

Sources: http://www.nku.edu/~issues/illusions/LateralInhibition.htm

Response to how do contact lenses work:

Contact lenses work to correct vision by applying the needed additional bending, in a particular direction, to incoming light passing through the cornea and lens. In the case of hyperopia where the eye is too short and lens too thin light is bent in a way that projects the image beyond the retina. The corrective lens used here is a convex lens. This lens works by forcing the light to converge earlier than it would and hence form an image on the retina instead of beyond the retina. In the case of myopia (I am slightly myopic) the eye is too long and the cornea and lens (perhaps too thick) bend light in a way that converges too soon projecting the image before the retina. The corrective lens for this is a concave lens that allows the light to diverge a little bit more until the image can be projected correctly on the retina. Note that these conditions of hyperopia and myopia can be fixed temporarily by moving closer (myopia) or farther away from the object (hyperopia). This temporary fix results from the bending of the lens as one moves closer or farther away from the object of interest.

I can hear me now…!

       Recently, I have been battling a stubborn head cold and tonight it allowed
for an interesting effect that I would like to share.  I usually do not
like feeling stuffed up when fighting a cold so I am always in the habit
of blowing my nose frequently to clear my head.  However, after the second
week into the cold I started experiencing an interesting effect where
anytime I blew my nose my ears would get significantly blocked up.  I was
frightened at first because when it initially happened I got a little
dizzy and even though I tried yawning or swallowing to depressurize my
middle ear I could not shake the blocked feeling. The sensation was akin
to my ears being blocked with water after swimming.  Apprehensive, I
resigned to blowing my nose less frequently or with less force than I
usually do to reduce the occurrence of this strange sensation (it still
happened many other times regardless of these precautions).
        Today was to be a good day because I had not blown my nose for awhile or
felt my head being stuffed. However, when I went to a party I started
experiencing something completely bizarre.  I was sitting next to a
window when I began perceiving sounds differently from one ear.  I began
hearing echoes from my left ear even noticeable in my own voice.  And
most sounds became piercing and painful (even voices of friends).  I was
forced to leave the party due to the shear discomfort of the experience.
The sensation has now reduced after blowing my nose again (resulting in a
stuffed head sensation), but I still have a troubling feeling in my left
ear.  It feels almost like the ear is now receiving less auditory stimuli
than the right ear.  I hope it is nothing serious and perhaps the strange
occurrence was just my ear being stuffed up all day without my knowledge
and depressurizing at that moment bringing in a flood of quality sounds
that became unpleasant.

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Smell is often described as the “fallen angel” of the senses. Why is that?

     I believe this is because we tend to take our sense of smell for granted
and only think of it when we perceive unpleasant odors.  We do not focus
too much on it for our everyday activity which I believe is a grave
mistake because it is so integral to everyday social experiences. Many of
the things we enjoy in life, whether it is sitting by the boardwalk as the
ocean breeze blows by, or salivating at the smell of food in the kitchen
or even savoring the taste of food that we eat can be associated with the
sense of smell.  In fact all our perceptual experience may be tied to
smell in some shape or form as was hinted at in the story The Dog beneath
the Skin in Sacks “The Man who mistook his Wife for a Hat.”  In this story
we see a young medical student who experiments with various amphetamines
like PCP and cocaine and consequently experiences a dream where he is a
dog.   In his dream he is able to appreciate the smells of various object
unlike he had ever done before.
      The bizarre part about this is that when he awakes he finds that his nose
is still overtly sensitive to smells. He describes his experience not only
referring to the additional powers that the sense gives him like being
able to smell his way around New York by the distinct smells of shops
(this is no easy feat as I am from New York and can attest to the shear
amount of different smell that can occupy just even the smallest of areas
let alone an entire neighborhood), but also describes an overall increase
in his sense of visual perception (noting the vibrant quality to color
hues) and his emotional sense detector.  He could smell a person’s
emotion—whether fearful or content.  He could also smell and recognize
people before he walked into a room and be 100% correct in his
identification.  What’s more interesting is that he did not feel as if
this was some new ability rather he postulated that it was simply himself
being more awake.  That is, in other words, in our every day life we are
constantly living half awake, half alive and using our powerful sense of
smell to only a portion of its true abilities.  I think we need to start
looking for a way to give this angel back its wings, although I do not
think using amphetamines is the way to go.

Jan 27 post

I found the brief mention of unilateral neglect to be particularly interesting because it dealt with a topic I had recently covered in one of my other classes. I had just read Oliver Sacks “The man who mistook his wife for a Hat.” And I was particularly interested in the case of the man who fell out of bed. The case was about Dr. P, a man who was described in the book as feeling perfectly fine the day he came into the hospital with complaints of paralysis and laziness in one of his leg and then after going to sleep at night woke up to find what he believed was a strange leg in his bed. He decides to throw the leg away thinking a nurse had played a New Years joke on him but found himself flying out of the bed with the leg.
Furthermore, he began striking at the leg and trying to rip it off as he now realized the strange leg was attached to him. Using the books (Perception fifth edition) definition to account for Dr. P’s case it would seem he lost communication between his visual and somatosensory regions in the parietal lobes that what he saw and felt were so completely different that he could not recognize his own limb. However, I found this to be even more bizarre than the case mentioned in the book (Perception) because this seemed to have happened so suddenly. I mean he was fine in the morning, so how can such a disconnect have happened so rapidly that even when questioned about the location of his leg, if the leg currently attached was not his own, he still could not even rationalize that that must have been his leg. I think there may have been more than neglect going on in this particular case.