Reading Activity Week #4 (Due Monday)

I thought the section in the book about aliasing was interesting. Aliasing is the misperception of grating due to under sampling. The Diagram in the book demonstrated that if the photoreceptors overlapped on the stripes that the result will be more grey but if they did not overlap you would be able to perceive the stripes. I think this is interesting because people always think they can see exactly what is there, but we can’t. This is something I would like to learn more about in class.
I also thought the part in the chapter that explained what 20/20 vision meant when pertaining to the Snellen test was interesting because it was something that I didn’t know. The Snellen test is that vision chart they use in schools, and eye doctor’s offices to see how well you can see. The top half of the fraction is the distance at which a person can identify the letters, the bottom half of the fraction is the distance at which a person with “normal’ vision can identify the letters. So the number on top is usually the one that changes to fit your particular eye sight. I like the little things like that in which you don’t think of and when you read about them you go, oh yeah that makes sense.
Another thing I found interesting in the book was that when you are asleep even if your eyes are open you are not actually able to see through them. I found this interesting because one of my friends sleeps with her eyes half open most of the time. It is really creepy and we always wonder if she can see us, or if she would be dreaming about us because her eyes are kinda open. Anyways, this answered our question, no she can not. So the Lateral geniculate nucleus (LGN) is part of the thalamus. When you go to sleep the thalamus sleeps too. So the information will go through your retinas and to your LGN but not any farther.
One thing I didn’t find that interesting was the simple vs complex cells. A simple cell is a cortical neuron with clearly defined excitatory and inhibitory regions. A complex cell is a neuron whose receptive field characteristics cannot be easily predicted by mapping with spots of light. I think I didn’t find that part as interesting because I wasn’t really clear on what was going on with the diagram, or what they were talking about. I think more information on this process would be good for class.
The thing in the chapter I think is going to be most useful in understanding sensation and perception is the part of the chapter that went thought how the image got from your retina to your striate cortex. This is something I would like to learn more about.
Terms: Aliasing, photoreceptors, Snellen test, Lateral geniculate nucleus (LGN), thalamus, retina, simple cell, complex vell, striate cortex

One thing that I found to be interesting was the physiology of the visual neurons. How the left LGN organized only the stimuli from the left of the blind spot (the right visual field) and visa versa. Also how this ordered neural pathways follow a specific path to the primary visual cortex. More specifically, how the areas closer to the fovea were given more brain area for processing (cortical magnification).
One area that I found interesting, and also found a little confusing, was the properties of the receptive-field neurons. There are millions of individual cells in the visual cortex, but each one responds to specific orientation, size, or length. This is absolutely remarkable, but it seems somewhat inefficient.
Another area that fascinated me was the orientation maps in the visual cortex. This picture given in the book may make it seem like the layout is complete chaos, but in about every 1mm square area is an even amount of cells with specific orientations. These hypercolumns are given enough cells to completely take in all stimuli (for a small region of the eye).
One are that didn't interest me as much as the other sections was the selective adaptation section. This was a very interesting concept to learn, but most of this section was committed to showing that the previous research (Hubel and Wiesel) could also pertain to humans. While this is important for research purposes, it wasn't necessarily important for understanding the concepts of spatial vision.
I think the most important information that was learned in this chapter was the overarching information processing in the visual cortex. Not only does this area take in all the visual information, but this is where sensation meets perception.
I would like to understand more about the visual cortex and how it communicates the information it has gathered with the rest of the brain.

Terms: lateral geniculate nucleus, primary visual cortex, fovea, receptive-field, hypercolumns, selective adaptation, spatial vision

After reading chapter 3, I found many things interesting but I found a few concepts particularly enjoyable to read about. One concept I enjoyed reading about was visual resolution acuity. Acuity is the smallest spatial detail that can be resolved. Optometrists refer to this acuity in terms like 20/20. Visual scientists use different terminology; they talk about the smallest visual angle of a cycle of the grating that a person can perceive. In regards to a grating, a cycle is a pair consisting of one dark bar and one bright bar. It’s a repetition of a black and a white stripe. A visual angle is formed by lines going from the top and bottom, or left and right, of a cycle through the center of your lens, and then to the retina. I enjoyed reading about this because I never fully understood what the optometrist was talking about, or how they got the measurements, for my vision strength. When you visit the optometrist, you read a series of letters decreasing in size until you start making several mistakes in identifying the letters. Your doctor will tell you your vision acuity is 20/30 if you need glasses, 20/20 if your vision was good or 20/10 if you could read all the letters on the chart. This method was invented by Herman Snellen in 1862. He defined the visual acuity of a patient being tested as “the distance at which the patient can just identify the letters divided by the distance at which a person with ‘normal’ vision can just identify the letters.” Later on, the test was changed to set the patient at a constant 20 feet distance, and the letter size was altered instead of the patient’s position. Thus, normal vision was defined as 20/20, but most healthy young people have a 20/15 acuity level. I on the other hand cannot see anything beyond 3 inches from my face without my glasses or contacts.

Another concept I found interesting were columns and hypercolumns, because I think it is cool how millions of neurons respond to different stimuli (stripes, edges, gratings, etc). Hubel and Weisel found early on that various receptive-field properties weren’t scattered haphazardly around the striate cortex. They discovered what each cell was looking for (stripes, spots, etc) and then found if they pushed a recording electrode down through the layers of the cortex in a perpendicular direction from the cortical surface, all the cells they encountered showed similar orientation preferences. If they moved the electrode a short distance over, the cells now responded to a slightly different orientation. Hubel and Weisel concluded that neurons with similar orientation preferences were arranged in columns that extended vertically through the cortex. When they inserted the electrode in a parallel orientation to the cortical surface, they found a progressive change in preferred orientation. Almost all the orientations were encountered at a distance of about .5 millimeters, and this has been confirmed using other physiological techniques. Hubel and Weisel proposed that a 1 mm block of striate cortex contained “all the machinery necessary to look after everything the visual cortex is responsible for, in a cettain small part of the visual world.” Each of these sections of cortex is called a hypercolumn. It contains at least two sets of columns, each covering every possible orientation. One set prefers input from the left eye, and one set prefers input from the right eye.

I also enjoyed reading about strabismus, because I like learning about maladies, and correcting this condition later in life will have little effect. Hubel, Weisel and many others, showed that there is a critical period of early visual development when normal binocular visual stimulation is required for normal cortical development. In humans, this time period is the first three to eight years of life. During this period cortical neurons are being wired to their inputs from the two eyes. If one eye isn’t getting normal stimulation, the neurons that should respond to that eye don’t become properly connected. Some evidence shows that these neurons are actually co-opted by inputs from the other (normally functioning) eye. If cataracts or strabismus are left untreated during the critical period, the misplaced cortical connections can never be repaired. Strabismus is a misalignment of the two eyes so that a single object in space is imaged on the fovea of one eye, and on a nonfoveal area of the other (turned) eye. Unfortunately, correcting this condition later in life will have little effect because the information from the newly-functioning eye can never be properly conveyed to or processed by the cortex.

I found the concept of simple and complex cells the least interesting because it seems like we have already discussed this concept in other classes. Simple cells are cortical neurons with clearly defined excitatory and inhibitory regions. Other neurons show responses that cannot be simply predicted from their responses to stationary bars of light. Hubel and Weisel called these complex cells, these will respond regardless of where the stripe is presented, as long as it is somewhere within the cell’s receptive field. They cannot be easily predicted by mapping with spots of light. Simple cells are “phase-sensitive” and complex cells are “phase-insensitive.”

I think the concept of how information is transformed from the circular receptive fields of the retinal ganglion cells to the elongated receptive fields of the cortex is very important to understanding Sensation and Perception, and will be helpful for future readings and discussions because it’s another building block of how the world around us is perceived by our body.

I would like more information about columns and hypercolumns because I thought it was interesting to read about. I would also like more information about the lateral geniculate nucleus, because I don’t think I fully understood it from reading the chapter.

Terms: visual resolution acuity, acuity, visual angle, cycle, grating, acuity level, columns, hypercolumns, receptive-field properties, striate cortex, cortex, cortical surface, strabismus, binocular visual stimulation, cortical development, cortical neurons, cataracts, fovea, simple and complex cells, lateral geniculate nucleus

After reading chapter 3, I found a couple of terms/topics that were of interest to me. Lateral geniculate nucleus was a term that was of interest to me. It was defined as a structure in the thalamus, part of the mid brain that receives input and output connections to the visual cortex. The LGN’s act as a relay station from the retina to the cortex. It’s made up of a six-layered structure with the first 4 layers on top responding to stationary targets and the bottom two layers for fast moving objects. The top four layers are called parvocellar layers and the bottom two are magnocellular layers. I found LGN’s interesting because they have a map of our complete visual field. Each layer has a number that corresponds to a side of the vision field. The right side of the LGN responds to 1, 4, and the 6 layers of the left part of the LGN and the left side responds to 2, 3 and 5 of the right side. I found it this interesting because this is how we are able to see the same thing with both our eyes. They help each other out to create a full picture.
Another topic I found of interest was simple and complex cells. Simple cells are cortical neurons with clearly defined excitatory and inhibitory regions. Complex cells are neurons whose receptive field characteristics cannot be easily predicted by mapping with spots of light. I liked that fact that simple cells help us determine light on one side or the other, or light with a specific width. Complex cells differ from simple cells in the fact that it will respond to the light source regardless of where it is located.
One last thing I found interesting was spatial-frequency channel. Spatial-frequency channel is a pattern analyzer, implemented by an ensemble of cortical neurons, in which each set of neurons is tuned to a limited range of spatial frequencies. There are two main frequencies that I found cool. High-frequencies are used to determine fine detail in a picture and low frequencies are used to determine broad outlines of a picture. I found it interesting that when you put the two frequencies together, that you got full picture.
The thing I found least interesting was spatial frequency. I didn’t really understand the whole part about the visual angles of objects and the cycles per degree of dark and bright bars.
Lateral geniculate nucleus was probably the most insightful in the process of learning sensation and perception for me. I never really understood how we are able to take both our eyes and combine what they see into one complete picture. I think that’s really important to understand when we look at our vision as a whole.
Two topics I would like more information about would be spatial frequency and contrast threshold.
Terms: Lateral geniculate nucleus, spatial frequency, cycles per degree, contrast threshold, simple cells, complex cells, neurons, spatial-frequency channel, parvocellar layers, magnocellular layers, retina, cortex.

I found the idea of special frequency and retinal ganglion cells to be interesting. I found this to be interesting because only at medium frequency and when special frequency is just right can our cells have a good response. Our cells respond well to gratings of just the right size (if the stripes are just the right size and distance apart our cells will have a high response). So if there is low frequency our cells will have a weak response. We will also have this response if the frequency is too high.

Along with finding special frequency and retinal ganglion cells to be interesting, I found special frequency and pattern analyzers to be interesting. This was interesting because the example in the chapter is relatable. It gives us reasons why low frequency and high frequency is important in our vision. When we see different information we use different degrees of special frequency. To determine the boarders and the edges of an image we need low frequency and to determine fine details in an image we need high frequency. So in order for us to determine a pattern we need both high and low frequency.

I also found it interesting when we don’t have normal visual experiences we will not have normal visual developments. This development is critical in the ages between 3 and 8 in humans. If one eye sees something and the other does not see that same thing it can cause a loss of special vision. I found this to be interesting because it is abnormal, if visual neurons are not treated between the ages of 3 and 8 or right away it can cause amblyopia, which is reduced spatial vision in eyes that could have had normal spatial vision.

I found the information about the lateral geniculate nucleus to be uninteresting. This was uninteresting to me because it was a lot of information to take in and it was confusing. I found it hard to understand how the information is processed to the brain.

In this chapter I thought the information about selective adaptation was most useful in sensation and perception. This is useful because it gives us information about how the human visual system works, and how our neurons adapt to different stimuli.

I would like to know more about amblyopia and the development of spatial vision. For the development of spatial vision I would like to know more about how early it develops in infants and why infants prefer more complex images.

Terms: special frequency, retinal ganglion cells, medium frequency, gratings, pattern analyzers, low frequency, high frequency, amblyopia, lateral geniculate nucleus, neurons, selective adaptation

One interesting part of this chapter finally made me understand what my eyesight means. Eye doctors have always told me that I have 20/15 vision, and that my vision was better than normal, but I was never aware of what this actually meant. 20/15 vision means I have excellent vision and that what a normal person can read at 15 feet, I can read at 20. This eye test was developed by Herman Snellen back in the 1862. Although I have great vision now, it will likely deteriorate over the course of my life due to presbyopia. This has happened to both of my parents who now wear bifocals. My moms vision is something like 20/500. The discoveries of Hubel and Wiesel are another thing that I found interesting. Orientation tuning is where neurons do not fire as fast for certain orientations of objects as they do for other orientations of the same object. This happens in the striate cortex which is the area in the brain which processes visual information. Another property in the striate cortex is that some cortical cells respond differently to moving lines, bars, edges, and gratings and that their response times are different depending on how fast they are moving. Another thing that I thought was interesting was that babies have a pretty developed visual system. I thought this was interesting because you usually think of babies as being pretty helpless.

I still have trouble understanding the different parts of the eye and how they are interconnected.

Terms: presbyopia, bifocals, orientation tuning, striate cortex,

I found a lot of the material quite interesting in this week's chapter. I think Hubel and Weisel's work studying the receptive fields of retinal ganglion cells is very fascinating, if only for the fact that the method behind their techniques was so nuts-and-boltsy. Discovering the orientation tuning of neurons in the striate cortex could only be accomplishing through a great deal of trial and error. It is interesting to know that not only are lines themselves important to our visual system, but also that there is a gradation of perceptual interest based upon the positioning of these lines!
A related section that I enjoyed was the part about spatial frequency channels. Each of these channels is thought to be tuned to a different range of spatial frequencies, which allows us to more effectively analyze patterns in our environment. It is cool that we detect these variations in patterns independently, even when combined. This is also why we can shift our perception from broad, rudimentary features to finer levels of detail.

Cortical topography and magnification was also quite fascinating because it elaborated on how the size and topographical location of objects is mapped onto the visual cortex. Objects viewed at an angle closer to the fovea are much more highly magnified than those at angles as you move further outward. This is because the more densely packed photoreceptors are located in this area, and there is not enough room or visuocortical resources for a larger area to be devoted to higher-resolution vision. I found the section on simple and complex cells to be the least interesting, if only because it seemed to be fairly intuitive. As you might expect, complex cells have a higher receptive range than a complex cell and provide increased firing rates. In class, I would like to learn more about columns and hypercolumns and spatial-frequency channels.

Terms: receptive field, retinal ganglion cells, orientation tuning, striate cortex, cortical topography, cortical magnification, visual cortex, fovea, complex cell, simple cell, column, hypercolumn

Three things I found interesting in this chapter was, first was contrast threshold, which is, the smallest amount of contrast required to detect a pattern. I guess I really don’t know why I thought it was interesting, but it just reminded me how you can look at a TV screen, or a computer screen that’s in sleep mode and tell its still on because it’s a darker shade of black on the screen when its off, and this showed the science of the slight contrast in color. The second thing I found interesting was the tilt aftereffect. Tilt aftereffect, according to the text, is the perceptual illusion of tilt, produced by adaption to a pattern of a given orientation. The reason I thought it was interesting was because of that test that you can try out in figure 3.26. I just thought it was neat how your eyes can play tricks on you like that just by looking back and forth between two pictures like that. Another thing I found interesting was spatial vision. Spatial vision is vision in large block shaped colors with varying contrast. I just thought it was interesting how they talked about the assumed similarities of infant vision to spatial vision.

The thing I found least interesting was the section about columns and hypercolumns. I found this section really hard to follow and caught myself drifting off while reading it. The thing from this chapter that I think will be most useful in understanding sensation and perception is the first part of this chapter where they describe parts of the eye and what they do. I feel that understanding that would be one of the most important things for you to know to be able to fully grasp what sensation and perception is.

I would like to know more about spatial vision, and contrast threshold.

Terms used- contrast threshold, tilt aftereffect, spatial vision

I personally enjoyed reading the material covered on eye tests. Eye testing was created by Dr. Snellen where he created a formula to find the distance that a person can identify letters. I found it rather interesting to learn more about how the measurements are taken and that visual acuity in the average healthy adult is 20/15. There is also a lot of information that deals with work done by Otto Schade. He studied what It took to detect gratings referring to the term spatial frequency. Spatial frequency is the number of times a certain pattern repeats in a unit of space. Schade was also an important historical figure for his findings on the contrast sensitivity function. This can be more readily demonstrated with the inverted U shape that helps show humans contrast threshold. In regards to contrast sensitivity function, another thing from the text I found interesting included the information on what can be referred to as spatial-frequency channels. Since there is a falloff on the inverted U shape of contrast sensitivity with low spatial frequency, findings suggest this may be due to less neurons within low spatial frequency. Low frequency images show a more broad outlines, such as the face pictured in figure 3.30, where high frequency shows much more finer details, such as the wrinkles in the face. Another image that demonstrates spatial frequency is seen in figure 3.31 where high spatial frequency disguises low spatial frequency. Studying spatial skills and vision is much harder in infants as well. This is very interesting information that we are still able to detect how the visual system in young children looks based on VEP’s. I believe this will be useful in understanding sensation and perception, because of how crucial the visual system actually plays from an early onset age. A Condition called strabismus, or turned eye, is a diagnostic condition of misalignment of the eyes, an image on the fovea in one eye while the other image is on the nonfoveal in the other. This often may lead to amblyopia, which is defined as reduced special vision, or more commonly known as lazy eye. These concepts help me to understand spatial perception from an early onset that can have potentially serious effects on our visual system. If noticed at an early onset of its course, vision can be corrected. But with abnormal conditions comes a greater risk of losing normal spatial skills. One concept I had some trouble grasping was selective adaption and the section of selective adaptation for spatial frequencies. Two terms I would like to gather more information on are columns and hypercolumns. I think finding out the insight to what Hubel and Wiesel found would give me a greater understanding of the receptive-field properties and how they relate with cells to produce neuron signals and messages.
Terms: spatial frequency, contrast sensitivity function, contrast threshold, spatial frequency channels, strabismus, amblyopia.

I found the explanation of what 20/20 vision means was really interesting because I really didn't know what it meant when I went to the eye doctor. I simply just thought it was the best, so I enjoyed knowing that I was. I now enjoy knowing why! I was actually disappointed when I learned that 20/30 is better than 20/20. I thought it really interesting that the reason we are put at 20 ft. is because that is simply what the researchers had come up with at the time of the study. We could have picked other distances, but I guess 20 was the best! I found it interesting that they could actually say that there is "normal" vision. I have always thought vision might be a little different for everyone, in that so many people have glasses and different things going on in their eye. But I am slowly learning that our eyes work in basically the same way.
Secondly, I found topographical mapping very interesting. I was always very confused that our vision was perceived through our eyes, and processed through the opposite side of our brain. I learned that the two lateral geniculate nuclei (LGNs) are the reason why. LGN's are structures in our thalamus that receive info from our ganglion cells and gives input and output connections to the visual cortex. Basically the thing that helps perceive what we are looking at. Almost like a messenger. The book describes the LGNs as a layer of pancakes. The two bottom layers are the magnocellular layers. I found them interesting because they are actually specialized to respond to large, fast-moving objects. It's crazy that we have one thing in our body that is paying attention just to this alone. As well as the top four layers of the LGNs are the parvocellular layers. They are specific to respond to processing details of stationary targets. Awesome.
The third thing I found interesting about chapter three was the story about the girl who almost couldn't see stripes. I mainly thought this was interesting because it brought all of the hub-a-loo of the scientific talk into a story, which makes it more fun and interesting for me to comprehend. The story said the girl had 20/1200 vision! This means that the vision of a person with "normal" vision see's what she saw at 20 ft. at 1200 ft.! Crazy!
The part I didn't really enjoy about chapter three was the tilt aftereffect and selective adaptation. I was frustrated because I didn't understand it and would have liked to. The pictures look interesting, and I wanted to test what it was saying in the book, but I simply just didn't understand.
Gosh, it's hard to pin point one topic that is the most useful in understanding sensation and perception in this chapter. I would have to say that all of it is really important in understanding it. Some things more interesting than others, but we already went over that.
One thing I would like to learn more about is adaptation and tilt aftereffect. I just need to research them more to understand them. I also would like to research more cases on lazy eye. It was very interesting to me to hear about people dealing with it and how they got over it. Especially in third world countries.

Terms: topographical mapping, lateral geniculate nucleus (LGNs), magnocellular layer, parvocellular layer, adaptation, tilt aftereffect.

Chapter 3 for this week is entitled Spatial Vison.

I enjoyed learning about columns and hypercolumns. It was one of the only subjects I actually understood in this chapter. A column is just defined by a bunch of neurons arranged together and a hypercolumn is a building block of columns together to form a large neuron block. I found it interesting that hypercolumns can be made up of neuronic material for both the left eye and the right eye. This information isn't separated. These hypercolumns receive input from the right or left eye in order to function the brain.

Second, I enjoyed the part of the chapter about selective adaptation. It was slightly confusing, but basically, the eyes are able to adapt to what they are looking at by making a reduction in their responses. This can alter vision and also make the subject have an altered perception as to what they are looking at. With this adaptation, there is a tilt aftereffect that is defined as an illusion (or perception) of a tilt which has been altered through selective adaptation in the eye. This shows one of the reasons why different neurons only respond to certain orientations in the eye. I still don't fully understand this concept, which is why I would like to learn more about it!

Third, I enjoyed reading about a disorder called strabismus. This is when one eye is tilted and never sees anything in a "normal" light. The whole time I was reading about this, I was thinking about Mad-Eye Moody in Harry Potter because he has a tilted eye. I don't really know how strabismus works which is why I will be doing my topical blog on this subject. I liked learning that people with this disorder don't technically see things "wrong", they just have a different view of the world.

I don't really think this chapter is that important or connected to other chapters because it talks about a specific functioning of the eye. If it did though, I would think that understanding spatial functioning and its relationship to vision would be very important!

I was so confused about what Sine Wave Gratings. I did not understand this concept at all and I got very frustrated looking at it. I have heard of spatial frequency in other classes before and understood it, but putting it into the concept of sine wave gratings confused me. Even the books definition is different from what I thought I knew before that. I feel like I need to look more into this topic in order to understand it more.

Sine wave gratings, Spatial frequency, column, hypercolumn, adaptation, tilt aftereffect, strabismus