Please read chapter 6. After reading chapter 6, please respond to the following questions:
What were two things from the chapter that you found interesting? Why were they interesting to you? Which two things did you find the least interesting? Why? What did you read in the chapter that you think will be most useful to in understanding the history of psychology? Finally indicate two topics or concepts that you would like me to cover in more depth in class.
Include a list of the terms and concepts you used in your post. (example - Terms: positive reinforcer, extinction, reinforcer, discriminative stimulus...)
Let me know if you have any questions,
--Dr. M
I thought the very first few paragraphs on space perception and binocular vision were interesting. First of all, realism is a philosophical position arguing that there is a real world in which we sense. Positivists, who argue that all we have to go on is evidence of senses. This perspective points out that the world just might be nothing more than a hallucination. A very interesting concept I thought was Euclidean. This is named after the Greek geometer Euclid. This concept means that parallel lines stay parallel as they are extended in space. Also, objects remain the same size and shape as the move around in the spaces as well. For example, the angles of a triangle always add up to 180 degrees no matter in what space. another geometry is non-Euclidean when the three dimensional world is projected on the 2 dimensional retina. The retinal aread occupied by a certain object gets smaller as the object moves away from the eye. Therefore, parallel lines don't necessarily remain parallel and these triangles don't always add up to 180. The experiment with the finger (holding your left index finger up and holding the right one to the left of it, then closing the left eye and then the right) showed that the retinas are in slightly different places.
The next topic that i thought was interesting was the next topic. This topic is again about different topics in our visual field. The book states that our visual field is limited to around 190 degrees from left to right, and 110 degrees of that is covered by both eyes. Vertically, however, is only about 60 degrees up from the center and 80 degrees down from the center. Our visual field as well as others' visual fields help to spot fast moving objects in front of them that may help gathering food and prey (this may be part of evolution as well). Binocular summation is the combination of signals from each eye which make performance better with both eyes rather than just one eye. Binocular dispartiy, however, is the differences between to retinal images of the same scene or same world. THe book states that disparity is the basis for stereopsis, which is a vivid perception of the three-dimensional aspect of the world that's not available with monocular vision, or one-eyed vision. When we close one eye, we notice that our vision is somewhat limited. This is also worse in examples like mine where I have an astigmatism that cannot always stay focused. This makes me very glad to have two eyes that can in a way feed off each other and correct those areas of my vision that aren't exactly stable. Without two eyes, we wouldn't be able to perceive the world in the same way we do now. Along with this topic comes depth cues, which are information about the third dimension (or depth) of visual space. Monocular depth cues are available even when the world is seen with only one eye whereas binocular depth cues rely on information from both eyes.
A topic I found not so interesting was the topic of occlusion. Occlusion is a cue to relative order in which one object obstructs the view of part of another object. This is related to finding edges as well. It gives information about the relative position of objects. It is present in most visual scenes since objects we see are always blocking something else. The only time this isn't true is with accidental viewpoints. Also, occlusion is a nonmetrical depth cue, which provides information about the depth order (relative depth) but not depth magnitude (the example used was that his nose is in front of his face). Metrical depth cue provides quantative information about distance in the third dimension. That was a little difficult to understand for me which is why I thought it wasn't quite as interesting.
Size and position cues were also not quite as interesting to me, but it kind of goes alone with the first topic discussed in the book. Projective geometry is what describes the transformations that occur when the three-dimensional world is projected onto a two dimensional surface. Relative size is a comparison of size between items without knowing the absolute size of either one. For example, in figure 6.6 in the book. the balls are in an arc shape and appear to have different depth planes because they are larger and then smaller. The next term is texture gradient which is a depth cue based on the geometric fact that items of the same size form smaller image when they are father away. A variety of items that change in size across the picture will appear to form different depths. Also, relative height is also a depth cue, which is the observation that objects at different distances from the viewer on the ground plane will form pictures at different heights in the retinal image. Objects that are father away will be higher in the picture as well. This concept was easy to understand but I guess I found it kind of obvious so it was a little more uninteresting to me.
I think everything that was discussed about two eyes and evolution was the most useful in understanding the history of psychology. I'd like to talk about The different perspectives such as aerial perspective (a depth cue based on the implicit understanding that light is scattered by the atmosphere) and linear perspective (based on the fact that lines that are parallel in the three-dimensional world will appear to converge in a two-dimensional world). I'd also just like to talk about all the different cues in general as well.
Terms: binocular summation and disparity, monocular, stereopsis, depth cues, occlusion, nonmetrical depth cue, metrical depth cue, projective geometry, relative size, texture gradient, relative height, aerial and linear perspective.
In your first paragraph you talk about the non-Euclidean when the three dimensional world is projected on the 2 dimensional retina. The retinal area occupied by a certain object gets smaller as the object moves away from the eye.
It reminds me of when Dr. M had the picture of the pin-wheel up and it appeared 2 dimensional. He then brought it into 3 dimensional view. It was awesome and reminds me of your blog.
Two things that I found interesting in this chapter are: binocular summation and free fusion.
Binocular summation is the combination of signals from each eye in ways that make performance on many tasks better with both eyes than either eye alone. The author gives an example of rabbit's vision comparing to human's vision. Rabbit's visual field extends a full 360 degrees where our visual field is limited to about 90 degrees from left to right, 110 of which is covered by both ye. About 60 degrees up from the center and 80 degrees down.
Binocular visual fields give better chance to spot small, fast moving objects in front of them. Yet, from binocular summation we do not get much benefit because the 50% to 75% benefits assumes two completely independent person.
Another subjects I would like to mention is free fusion. It is the technique of converging or diverging the eyes in order to view a stereogram without a stereoscope. John Frisby called this technique " the poor man's stereoscope" In the textbook there is an example and figure of two squares that have in each of it a smaller ones that when we cross our eyes hard, we should see four sets of squares and see that the little ones are not equal and that in the left one the small squares are moved more to the right and in the right one, moved more to the left. Thus, crosssing your eyes automatically leads your ciliary muscle to make your lenses more spherical.
The least interesting things were the section of physiological basis of stereopsis; lots of complicated graphs and topic of pictorial depth and pictures. ( the apparent point at which parallel lines receding in depth converge).
I would like to cover more in class topic about stereoscopes and stereograms - when we see different image to one eye and different image to the other eye. And topic about abnormal visual experience could be interesting to talk in more details about it.
binocular summation
free fusion
stereogram
stereopsis
Two things I found interesting in chapter 6 were anamorphosis and free fusion. Anamorphosis is using linear perspective to create a distorted image that only looks correct when seen from a certain angle. There were some examples in the book that looked really cool. I think it’s amazing how an artist can create an image like that. This relates to our visual system because of what causes us to see an anamorphic image: the pictorial depth cue. The pictorial depth cue is a cue produced by the projection of a three-dimensional image onto a two-dimensional surface of the retina.
The other thing I found interesting is the concept of free fusion. Free fusion is “the technique of converging/diverging the yes in order to view a stereogram without a stereoscope”. A stereoscope is a device created that presents one image to one eye and another image to the other eye. The stereoscope was used as entertainment to be able to see three-dimensional images of places all over the world. Free fusion was discovered by John Frisby as a way to look at images three-dimensionally by crossing your eyes instead of using a stereoscope. To free-fuse, you look at two images side by side and cross your eyes until you see the image three times. I think this is interesting because it’s a simple technique but it explains a lot about our visual system and especially depth.
Two things I found least interesting were Bayesian Approach and Euclidean. Euclidean is the geometry of the world named after the Greek geometer, Euclid. I don’t think this is interesting because I dislike geometry and although it refers to our world, it doesn’t help me to understand anything about our visual system. The Bayesian Approach is a statistical model created after Reverend Thomas Bayes realized that prior knowledge influences our guess of the probability of a current event. I think this is uninteresting because I don’t see how it directly relates to the chapter except that we use prior knowledge to help understand or figure out what we see.
Although every concept has a history, I don’t think there was much information that helped me understand the history of psychology. Learning about the stereoscope was useful because it was created in the 1830s and led to free fusion which was discovered in the 1980s. As I talked about for chapter 5, knowing these theories can help you understand how psychology came to be as it is today, although I think there are way too many people and concepts involved that make it difficult to know everything.
Some topics I’d like to cover in class are horopter and Vieth-Muller circle. Another concept I couldn’t quite grasp was that of disparity.
Terms: horopter, Vieth-Muller circle, disparity, stereoscope, Bayesian approach, Euclidean, free fusion, convergine/diverging, depth, anamorphosis, linear perspective, pictorial depth cue, retina
Anamorphis cool, I agree. We always talk about how in lower and mid level vision the image is analyzed through its lines, to the extent that we have cells in the LGN and striate cortex that are tuned specifically to increase fire when stimulated by lines at different orientations. The principles that govern our sense of sight are largely based on the concept of the line and continuation of lines is something that our brain likes to see happen. Our brain perceives lines that appear to be continuous and from that specific angle that is the most probable assumption to make, but when we see from a slightly different angle we are able to tell that the lines are not continuous at all and we recognize the illusion. That is why motion cues are also incorporated with pictorial cues, because motion parallax allows our brain to process images from several different angles, assessing more information than just a static stimulus.
One topic that I found interesting in this chapter was size and position cues. Size and position cues are things that our eyes use to help us rapidly process the information gathered through our eyes. One aspect of size and position cues is projective geometry this describes the transformations that occur when the three dimensional world is projected onto a two dimensional surface. Another cue is relative size, or a comparison of size between items without knowing the absolute size of either one. However this cue can sometimes be thrown off, if you have ever seen two images that appear to be two different sizes, but they are actually the same size. Another cue is texture gradient; this cue is basted on the fact that items of the same size form smaller images when they are father away. Another cue is relative height or the observation that objects at different distances from the viewer will form images at different heights with objects farther away being seen as higher. Another type of cue is referred to as familiar size, this is a depth cue that is based on knowledge of the typical size of objects. This cue is used all the time, for an example you use this cue when you pick out an apple you know generally how big apples are. The final cues are relative metrical depth cue, which specify how far away something is without any information about the actual distance and absolute metrical depth cue with is a cue the provides absolute information about the distance in the third dimension. Another topic that I found interesting was Aerial perspective. At the heart of aerial perspective is the idea that more light is scatter when we look through the atmosphere, so the more distant the objects are subject to more scatter and appear fainter, bluer and less distance. An add on to this principle is that short wavelengths are scattered more than medium and long wavelengths this is why the object appears bluer. One topic that I didn’t find very interesting was stereoscopic correspondence, I didn’t find this very interesting because I found the topic difficult to read about and understand. Another topic that I didn’t find very interesting was abnormal visual experience can disrupt binocular vision. I found this section to be fairly short and difficult to understand. The two topics I would like to learn about further in class are binocular vision and stereopsis, as well as steroscopes and sterograms.
Terms
Projective Geo
Relative Size
Texture gradient
Relative height
Familiar size
Relative and Absolute metrical depth cue
Aerial perspective
Chapter 6 begins by explaining two opposing philosophical positions. Realism is a position that argues that there is an objective real world to sensation. Positivism says we go through life based on only evidence from our senses so that reality might not be anything more than an elaborate hallucination. The objective real world is called Euclidean because parallel lines remain parallel and objects remain the same size as they move around in space.
The chapter also describes the importance of binocular vision. It is noted that a three dimensional world can be created out of only one eye, but our visual field is very wide so stereopsis(the use of both eyes) helps us cue depth. The separate images from each eye are combined through binocular summation to improve our visual sensation.
The 3 dimensions that we perceive are constructed by both binocular depth cues and other depth cues that can also be picked up with only one eye. One such cue can be caused by occlusion, this is when an object obstructs the view of another that indicated their position in depth. Relative size and projective geometry also indicate where things belong in space. The chapter has many illustrations that show that our perception is based largely on objects relative to others. We don't measure everything we see so we take cues from objects around something we are looking at. Many interesting pictures are done by artists using anamorphic projection. This is when the rules of linear perspective make a 2 dimensional image so distorted that it only looks correct from a specific angle.
The portion of the chapter that I would like to be explained further is the latter portion of the chapter that describes the geometry of the eyes and how they focus on a particular object.
realism, positivism, euclidian, binocular vision, stereopsis, binocular summation, anamorphic projection.
The topics in Ch. 6 I found interesting was the discussion of monocular cues. A monocular depth cue is available even when the world is viewed with one eye alone. Although our world is three-dimensional our retinas only allow for a two-dimensional projection onto the surface of the retinas. For this reason our visual system needs depth cues from the visual scene to make inferences about the 3D world. Occlusion is a nonmetrical depth cue which provides information about the depth order but not the depth magnitude when objects occlude one another. A metrical depth cue on the other hand provides quantitative information about distance in 3D. Projective geometry is yet another monocular depth cue that our visual system implicitly understands and is related to the size and position of objects. Projective geometry occurs when a 3D world is projected onto a 2D surface (retinas). An example given is that in basic geometry parallel lines do not converge, however in projective geometry they do (linear perspective). The point at which the lines appear to converge is called a vanishing point.
Relative size refers to the comparison of size between items without knowing the absolute size of either one; the visual system assumes they are the same but if some are smaller they are considered to be further away. Texture gradient is when items of the same size form smaller images when they are farther away. Relative height, states that objects at different distances will form different heights at the retinal image. Familiar size is a depth cue based on preexisting knowledge of the size of objects and provides some metrical information. Relative metrical depth cues provide information of relative distance but not absolute distance two objects have from each other. Absolute metrical depth cue provides absolute distance information in 3D.
The visual system also implicitly understands information of the atmosphere. An aerial perspective, haze, is a depth cue with the understanding that light is scattered in the atmosphere and the more atmosphere looked through the more the light scatters, this results in more distant objects looking fainter, bluer or less distinct such as mountain peaks. Motion cues are important in our perception of the 3D world. One important motion depth cue is the motion parallax. Parallax occurs when your eye moves objects that are closer to you shift position more than those that are further away. A motion parallax is geometric information obtained from an eye in two different positions at two different positions in the head at the same time.
The topics I did not find as interesting was the discussion of binocular vision and stereopsis. Binocular cues make it easier for us to perform tasks, than with just one eye (binocular summation). Binocular disparity refers to the differences between the two retinal images of the same scene and is the basis for stereopsis, allowing us to use disparity as a depth cue, which is not available with monocular vision. If an image is formed at the same distance from the foveas this is called corresponding retinal points. Binocular neurons will respond better with these. The Vieth-Muller circle is an imaginary circle used to determine the location of objects which fall on corresponding points in the retinas. A horopter would be a Vieth-Muller circle with a surface of zero disparity which depends on the convergence of the eyes. Objects that are closer or farther away from the surface of zero disparity fall in noncorresponding points resulting in diplopia, double vision. In the area just in front of and behind the horopter objects will still be seen as one object. This is called Panum’s fusion area and allows for binocular single vision. At the age of 4 months old stereopsis appears suddenly. Stereoacuity, measure of the smallest binocular disparity that can generate a sense of depth, increases rapidly to adult levels by 6 months. Basic acuity on the other hand takes years to develop to adult levels.
I think the most important thing to help understand the visual system is how we combine the various depth cues to determine depth. The Bayesian approach, a statistical model that states prior knowledge could influence our estimates of the probability of a current event. Basically we take our variety of depth cues and determine the probability of the interpretations we can make from each cue.
Topics I would like to discuss more in class are: stereoscopes (device for presenting one image to one eye and another image to the other), stereograms, free fusion (technique of converging or diverging the eyes in order to view a stereogram without a stereoscope), stereoblindness (inability to make use of binocular disparity as a depth cue), and random dot stereograms. I think a further in depth discussion on how these work would help and they are interesting topics.
TERMS: monocular depth cue, nonmetrical depth cue, metrical depth cue, occlusion, projective geometry, linear perspective, vanishing point, relative size, texture gradient, relative height, familiar size, relative metrical depth cues, absolute metrical depth cue, aerial perspective, haze, motion cues, parallax, stereopsis, binocular summation, binocular disparity, corresponding retinal points, Vieth-Muller circle, horopter, diplopia, Panum’s fusion area, stereoacuity, Bayesian approach, stereoscopes, stereograms, free fusion, stereoblindness, and random dot stereograms
The topic that I found interesting in chapter six was the topic of monocular depth cues. Monocular means to view something with only one eye. There are various cues that help us perceive the depth of an object when we are only using one eye. These are referred to as monocular depth cues. Before venturing into the multiple depth cues, I would first like to mention that there are also depth cues that our visual system uses when using both eyes. These are called binocular depth cues. According to the text, Stereopsis (the ability to use binocular disparity as a cue to depth) is the primary example in humans, but convergence and the ability of two eyes to see more of an object than one eye sees are also binocular depth cues. (Binocular disparity, used in stereopsis, is defined as the differences between the two retinal images of the same scene)
There are several different monocular cues. The first one mentioned in the textbook is occlusion. Occlusion is not a new concept to this course. It is defined as a cue to relative depth order when on object obstructs the view of part of another object. The big issue that we can run into with occlusion is that we could experience an accidental viewpoint, which would mean that various odd shape pieces are not really behind or in front of each other but just appear that way due to your viewpoint. Occlusion can provide information that is either metrical or nonmetrical. A nonmetrical depth cue provides information about the depth order but not depth magnitude. Where as a metrical depth cue is one that does provide information about distance in the third dimension. Relative size is another depth cue. this is a comparison of size between items without knowing the absolute size of either one. Normally objects that are closer to us appear larger. This can be understood by the concept of a texture gradient, or an area of items that change in size across the image. Relative height can also be used as a depth cue. This is an observation that objects at different distances from the viewer on the ground plane will form images at different heights in the retinal image.
Familiar size is another depth cue that is based on knowledge of the typical size of objects. Aerial perspective is another depth cue that is based on the implicit understanding that light is scattered by the atmosphere. More light is scattered when you look through more atmosphere. Thus more distant objects are subject to more scatter and appear fainter, bluer, and less distinct. Linear perspective is a depth cue which according to the text is based on the fact that lines that are parallel in the three-dimensional world will appear to converge in a two-dimensional image. Thus far, most of the motion cues are based on a non-moving cue. There are motion cues that we use as depth cues as well. One of these are the motion parallax. According to the text this is based on head movement and occurs when geometric information is obtained from an eye in two different positions at two different times is similar to the information from two eyes in different positions in the head at the same time. The last types of monocular cues that are mentioned in the text are accommodation and convergence. Accommodation is the process by which the eye changes its focus and convergence is the ability of the two eyes to turn inward often used in order to place the two images of a gesture in the world on corresponding locations in the two retinal images. Divergence is the opposite of convergence and the eyes turn outward.
The second thing that I found interesting in this chapter was the short section that discussed the view of a rabbit. It was interesting to learn that they have a very large visual field, 360 degrees to be exact. This allows them to have a better chance of escaping predators.
Something that I didn't find as interesting as the rabits vision or monocular depth cues was the topic of Vieth-Muller circle, Panum's fusional area and the horopter. The Vietho-Muller circle is explaned in the text as the location of objects whose images fall on geometrically corresponding points in the two retinas. The horopter is the location of objects whose images lie on corresponding points, the surface of zero disparity. and the panum's fusional area is the region of space, in front of and behind the horopter, within which binocular single vision is possible. I would like to discuss these topics more in depth in class because I think it would help me better understand why they are important and what they can tell us about the visual system.
I think that knowing about stereoscopes and stereograms are helpful when trying to understand the visual system. Stereoscopes They give you a visual way of seeing how the two eyes see different things but still present on picture of the world you are viewing. stereoscopes were originally intended to help scientists study the eye but caught on to the general public as a way of entertaining. The are devices that present one image to one eye and another image to the other eye thereby creating a single, three-dimensional image.
The main topic that I would like to discuss in further depth in class would be the Bayesan approach. This is a statistical model based on reverend thomas bayes insight that prior knowledge could influence your estimates of the probability of a current event.
Terms: Monocular depth cues, monocular, binocular depth cues, stereopsis, binocular disparity, occlusion, accidental viewpoint, nonmetrical depth cue, metrical depth cue, relative size, texture gradient, relative height, familiar size, aerial perspective, linear perspective, motion parallax, accommodation, convergence, divergence, Vieth-Muller circle, Panum's fusional area, horopter, stereograms, stereoscope, Bayesian approach
Our visual field is limited to about 190 degree from left to right, 110 degrees of which is covered by both eyes. The field is more restricted vertically: about 60 degrees up from the center of gaze and 80 degrees down. Binocular visual fields give predator animals such as humans a better chance to spot small, fast moving objects in front of them that might provide dinner. In vision, this binocular summation principle may have provided the evolutionary pressure that first moved eyes to the front of some mammals and birds faces. Binocular summation is the combination of signals from each eye in ways that make performance on many tasks better with both eyes than with either eye alone. In addition, binocular disparity is the differences between the two retinal images of the same scene. Disparity is the basis for stereopsis, a vivid perception of the 3D if the world that is not available with monocular vision which mean with one eye. Stereopsis is the ability to use binocular disparity as a cue to depth.
What I first found interesting was monocular cues to 3D space. On the basis of the retinal images and an implicit understanding of physics and geometry, each cue provides a hint about the likely structure of the space in front of us and the disposition of objects in that space. Every view of the world provides multiple depth cues. Usually the cues reinforce each other, combining to produce a convincing and reliable representation of the 3D world. In relation to occlusions there is nonmetrical depth cue which provides information about the depth order (relative depth) but not depth magnitude. Also, metrical depth cue which provides quantitative information about distance in the third dimension. When it comes to size and position cues the image on the retina formed by an object out in the world gets smaller as the object gets farther away. Projective geometry describes how the world is projected onto a surface. For example, a shadow is a projection of an object onto a surface. Relative size is a comparison of size between items without knowing the absolute size of either one. In addition texture gradient, shows larger objects in one area and smaller objects in another. Because smaller is interpreted as farther away, this arrangement creates the perception of a ground plane receding into the distance. Texture fields that provide an impression of 3D are really combinations of relative size and relative height cues. Relative height is the observation of an object at different distances from the viewer on the ground plane will form images at different heights in the retinal image. Objects farther away will be seen as higher in the image. There is another depth called familiar size which is based on knowledge of the typical size of objects like humans or pennies. The relative metrical depth cue can specify an object. Relative size and height do not tell us the exact distance to an object or between objects. On the other hand, absolute metrical depth cue provides absolute information about the distance in the third dimension. When it comes to the aerial perspective or haze the more distant objects are to more scatter and appear fainter and less distance. Short wavelengths are scattered more than medium and long wavelengths. The real image gives a stronger sense of depth. When it comes to linear perspective which is based on the fact that lines are parallel in the three dimensional world will appear to converge in a 2D image. The core piece of projective geometry in this case is that lines that are parallel in the 3D world will appear to converge in the 2D image, except when the parallel lines lie in a plane that is parallel to the plane of the 2D image.
The second thing I found interesting was combing depth cues. None of the cues are foolproof, and non work in e very possible situation. For example, relative height produces inconsistent or misleading information if we can’t see the pint at which an object touches the ground. The Bayesian Approach gives insight that prior knowledge could influence our estimates of the probability of a current even. In our experience, all pennies are the same size. This familiar size cue is one source of prior knowledge. The ideal observer gives the best available information and the ability to combine different sources of information in the optimal manner it can be useful to compare human performance to that of an ideal observer. When it comes to illusions and the construction of space there is what is called a Ponzo illusion which is a situation in which we over interpret the depth cues in a 2D image. Ponzo illusion is not a by produce of depth cues at all. It argues that it reflects a more general aspect of the visual system’s response to titled lines and is related to illusions. When it comes to binocular rivalry and suppression objects in the world are often project images on out two retinas that don’t overlap (that is, the images fall on noncorresponding retinal points) and that the visual system is physiologically prepared to deal with these discrepancies via disparity tuned neurons in striate cortex and beyond. The visual system chooses instead to suppress one image and perceive the other. Binocular rivalry is the competition between the two eyes for control of visual perception, which is evident when completely different stimuli are presented to the two eyes. Our visual system will not actually combine perpendicular stripes, but instead will battle between vertically and horizontally striped patches, with regions of dominance growing and shrinking over time.
One thing I found least interesting was binocular vision and stereopsis. Corresponding retinal points state that points on the retina of each eye where the monocular retinal images of a single object are formed are at the same distance from the fovea in each eye. The two foveas are also corresponding points. The location of objects whose images fall on geometrically corresponding points in the two retinas is known as Vieth-Muller circle. Objects that fall on corresponding retinal locations are said to have zero binocular disparity. If the two eyes are looking at one spot such as a red crayon, then there will be a surface of zero disparity running through that spot. That surface is known as the horopter which is the location of objects whose images lie on corresponding points and have surface of zero disparity. Objects placed on the imaginary surface in the world will form images on corresponding retinal locations. Objects that lie on the horopter are seen as single objects when viewed with boy eyes. Objects significantly closer to or farther away from the surface of zero disparity from images on decidedly noncorresponding points in the two eyes, and we see two of each of those objects. This double vision is known as diplopia. Objects that are close to the horopter but not quite on it can still be seen as single objects. This region of space in front of and behind the horopter, within which binocular single vision is possible, is know as Panum’s fusional area. The larger the disparity, the greater the distance in depth of the objects from the horopter. In addition, there is crossed disparity (in front of the horopter) which objects are located in front of the horopter, and appear to be displaced to the left in the right eye and to the right in the left eye. Uncrossed disparity is the opposed and behind the horopter. Moreover, the stereoscope proved that the visual system treats binocular disparity as a depth cue, regardless of whether the disparity is produced by actual or simulated images of a scene. This is a device fro presenting one image to one eye and another image to the other eye. Approximately three to five percent of the population lacks stereoscopic depth perception, a condition known as stereoblindness, which is the inability to make use of binocular disparity as a depth cue. Stereoblind individuals might be able to achieve the perception of three sets of squares, but the little white squares will not pop out in depth. Stereoblindness is usually a secondary effect of childhood visual disorders such as strabismus, in which the two eyes are misaligned. There is such thing called correspondence problem (binocular vision) which the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye. There are two heuristics for achieving correspondence: the uniqueness and continuity constraints. The uniqueness constraint is the reality that a feature in the world is represented exactly once in each retinal image. Working in the opposite direction, the visual system knows that each monocular image feature (i.e., a nose or a dot) showed be paired with exactly one feature in the other image. The continuity constraint holds that, except at the edges of objects, neighboring points in the world lie at similar distances from the viewer. Moreover, the brain can make use of two different types of disparity information: absolute and relative disparity. Absolute disparity is where a difference in the actual retinal coordinates in the left and right eyes of the image of a feature in a visual scene. Relative disparity is the difference in absolute disparities of two elements in a visual scene.
A second thing I found least interesting was the development of binocular vision. The development of stereopsis in infants makes them essentially blind to disparity until about four months of age. Infants are essentially stereoblind before three months, with most infants showing a sudden onset of stereopsis between three and five months. Stereoacuity is a measure of the smallest binocular disparity that can generate a sensation of depth. Once an infant develops stereopsis, stereoacuity increases rapidly to near adult levels. Before four months, babies don’t respond to these stereoscopic stimuli. When it comes to abnormal visual experience possible disrupting binocular vision, there is a critical period. This period of time is when the organism is particularly susceptible to developmental change. During early visual development when normal binocular visual stimulation is required for normal cortical development. During this period, the visual cortex is highly susceptible to any disorder that alters normal binocular visual experience. Furthermore, some humans with two eyes that don’t point at the same spot in the world. This is not a uncommon disorder known as strabismus. In exotropia, one eye is pointed too far toward the nose “cross eyed” and in esotropia, the deviating eye is pointed too far to the side. In addition, exposure to lines tilted to one side of vertical will make vertical lines appear tilted to the other side which is known as the tilt aftereffect. On characteristic of the tilt aftereffect is that it shows interocular transfer (transfer of the effect from one eye to the other.) if we show the adapting lines to one eye, we can measure an aftereffect through the other eye. This result is generally taken to show that the cells responsible for the effect are binocular; they receive input from both eyes. Individuals who exhibited strabismus during the first 18 months of life don’t show normal interocular transfer. The brain suppresses one of two images in strabismus. For example, strabismus greatly reduces the number of binocular neurons in the visual cortex. Cells that would normally be driven by both eyes are dominated by one.
What I think would be useful to understanding the visual system is binocular vision and all the different types of cues that correlate with our space perception. When it comes to accommodation the process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects). This is how the human eye focuses. In addition there is convergence and divergence. Convergence is the ability of the two eyes to turn inward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (typically on the fovea of each eye.) Convergence reduces the disparity of that feature to zero or close to zero. Divergence is the ability of the two eyes to turn outward. The more we have to converge and the more the lens has to bulge in order to focus on the object. Convergence is used more than accommodation. Moreover, these cues are the only ones besides familiar size that can tell us the exact distance to an object. Furthermore, space perception and binocular vision use the geometry of the world known as Euclidean which means that parallel lines remain parallel as they are extended in space, that objects maintain the same size and shape as they move around in the space, that the internal angles of a triangle always add to 180 degrees and so forth. There are three basic cues, depth, monocular and binocular. Depth cues are information about the third dimension of visual space. Depth cues may be monocular or binocular. A monocular depth cue is a depth cue that is available even when the world is viewed with one eye alone. Binocular depth cues rely on information from both eyes. Another cue is occlusion which is relative depth order in which one object obstructs the view of part of another object.
The two topics I would like covered more in depth are motion cues which is an important depth cue that is based on head movement. The geometric information obtained from an eye in two different positions at two different times is similar to the information from two eyes in different positions in the head at the same time. The term parallax refers to the geometric relationship revealed: when your eyes move, objects closer to you shift position more than objects farther away when you change your viewpoint. Motion parallax provides relative metrical information about how far away objects are. Another topic is pictorial depth cues and picture just because I found it interesting. Pictorial depth cue is a cue to distance or depth used by artists to depict 3D depth in 2D picture. A realistic picture or photograph is the result of projecting the 3D world onto the 2D surface of film or canvas. When that image is viewed from the correct position, the retinal image in one eyes at least is formed by the 2D picture that is the same as the retinal image that would have been formed by the 3D world and hence we see depth in the picture. There is a vanishing pint which is an apparent point in which parallel lines recede in depth converge. In addition in anamorphic projection, the rules of linear perspective are pushed to an extreme in which the projection of three dimensions into two create a picture that is recognizable only from an unusual vantage point or sometime a curved mirror.
Key Terms: relative size, projective geometry, nonmetrical depth cue, metrical depth cue, occlusion, binocular depth cue, monocular depth cue, depth cues, binocular summation, binocular disparity, monocular, stereopsis, Euclidean, motion parallax, familiar size, relative metrical depth cue, absolute metrical depth cue, linear perspective, aerial perspective, texture gradient, relative height, pictorial depth cues, vanishing point, anamorphosis, Bayesian approach, ideal observer, binocular rivalry, absolute disparity, relative disparity, stereoacuity, critical period, suppression, exotropia, esotropia, strabismus, corresponding retinal points, Veith-Muller circle, horopter, diplopia, Panum’s fusional area, crossed disparity, uncrossed disparity, stereoscope, stereoblindness, uniqueness constraint, continuity constraint, and correspondence problem.
I found the part about motion parallax very interesting. Motion parallax is based on head movement. It’s the geometric information obtained from an eye in two different positions at two different times that is similar to information from two eyes in different positions in the head at the same time. So for example if you look out the window of a train or car the objects that are closer to you move more quickly than the objects further away. Motion parallax can provide a sense of depth in some situations in which other cues aren’t very effective. The disadvantage of this is that it only works when the head actually move; just, moving your eyes back and forth doesn’t work. I found this interesting because now I have a clearer idea why cats bobble their head before pouncing on their prey.
Another part I thought was interesting was the technique of free fusion which is crossing your eyes to view a stereogram without a stereoscope. And with this there are 3-5% of people who lack stereoscopic depth perception which is called stereo-blindness. This is an inability of binocular disparity as a depth cue. This is not usually for individuals who have lost an eye but for individuals who have sight in both eyes. Stereo-blindness can be a secondary to visual disorder like strabismus. I found this interesting because I was not aware that some people cannot get the full effect of a stereogram.
The subjects I found to be least interesting were that on the Euclidean geometry, which the geometry of the world is (like geometry we took in high school). I also disliked the part on abnormal visual experiences like that of strabismus with esotropia (one eye deviates inward) and exotropia (one eyes deviates outward).
Somethings I would like to see covered more in class would be stereopsis and the correspondence problem.
Terms: motion parallax, free fusion, stereogram, stereoscope, steroblindness, Euclidean geometry, strambismus, estropia, exotropia, stereopsis and correspondence problem.
I found the whole section about monocular cues to three-dimensional space interesting. I also found this information to be the most useful in my understanding of how we see. Depth cues are used to deduce aspects of the 3-dimensional world from our 2-dimensional retinal images. We then use these cues to assume the structure of the space in front of us and the location of objects in the space. There are multiple depth cues that are used. The first one is occlusion. Occlusion gives us hints about the relative position of objects. Occlusion is considered a nonmetrical depth cue, meaning it only gives us information of the order of the objects. The next cue is size and position cues. This section talks about projective geometry which describes how the world is projected onto a surface. When we look at a picture we infer that objects that are smaller are further away. The book shows a picture of a line of red balls. One side the balls are large and as you move down the line they get smaller. Our visual processing assumes that all the red balls are actually the same size so the ones that appear smaller must be further away. This is called relative size. A very similar cue to relative size is texture gradient. The difference between the two is organization. With texture gradient larger objects are in one area and smaller objects are in another. Another cue that is closely related in relative height. This states that "objects at different distances from the viewer on the ground plane will form images at different heights in the retinal image. Objects that are farther away will be seen as higher in the image". Another depth cue uses our knowledge of the normal size of objects to help use infer what we are seeing. This is called familiar size. Besides occlusion, these cues are relative metrical depth cues. With relative metrical depth cues we do not get exact information on the distance to or between objects but we do get a basic idea. With absolute metrical depth cue we can get the exact measurements to or between objects. The only cue that could be considered absolute is familiar. The next cue is aerial perspective (haze). This cue uses our knowledge or how light is scattered by the atmosphere. Objects or scenes that are further away will appear hazy because they are subject to more light scattering. The last cue that I found interesting and understood was linear perspective. This cue is based on the "rules that determine how lines in 3-dimensional space are projected onto a 2-dimensional image". The book gives a couple examples but when ever I've thought about this I think of a road. If you go to highway 20 and stand in the middle in the distance the road will seem to meet at a point in the middle of your visual field. This point is called the vanishing point. We know that 20 doesn't end anywhere near here. In a 3-dimensional world parallel lines will stay parallel and keep going but when it's put into a two-dimensional image the lines converge.
I didn't fully understand the information about pictorial depth cues and pictures. The text states that pictorial depth cues are "a cue to distance or depth used by artists to depict three-dimensional depth in two-dimensional pictures." The reason I brought this up even though I don't fully understand what they are saying is that I found the information about anamorphic (anamorphosis) projection extremely interesting. Artists who use this technique take the rules of linear perspective to create a picture that is only recognizable from one unusual position.
One part of the chapter that I found uninteresting was about accommodation, convergence, and divergence. Accommodations is the process used when the eye is focusing. In accommodation the lens gets fatter as we focus toward nearer objects and thinner as we focus on objects that are farther away. When we focus on objects that are closer our eyes rotate inward which is a process called convergence. When we focus on objects that are farther away our eyes rotate outward which is called divergence.
Another part of the chapter that I found uninteresting was the information on the Bayesian approach. The Bayesian approach was named after the Bayes Theorem of statistics. The approach says that "prior knowledge could influence our estimates of the probability of a current event". From what I gather from reading this section the approach uses prior knowledge and probabilities to determine what is being seen.
A few things I would like to go over in class are the Vieth-Muller circle, horopter, diplopia and Panum's fusional area.
Terms: monocular cues, depth cues, retinal images, occlusion, nonmetrical depth cue, projective geometry, relative size, texture gradient, relative height, familiar size, relative metrical depth cue, absolute metrical depth cue, aerial perspective, linear perspective, vanishing point, pictorial depth cues, anamorphic projection, accommodation, convergence, divergence, Bayesian approach
Loved this chapter. I found myself very interested in how we perceive depth and distance. Our depth perception ability taps into object recognition, motion and direction recognition and even ingrained adaptations to our planet. I had also thought of depth perception as a pretty simple and straightforward process but it seems to be a pretty high order ability needing several parts of the brain to interpret the visual field before depth can be determined and distance assigned. We perceive depth in two ways. We use one eye and harness neurocognitive structures that recognize cues, implying that depth and distance are present. Monocular cues are interpreted from information collected by one eye. This implies that at this point two areas in the brain are processing different information at the same time, one on each side corresponding to each eye, or more likely each half of the visual field. Several principles are theorized to be the fundamental factors upon which our cognitive recognition of depth depend on. The first of these is known as occlusion. This principle holds that we recognize the edges of objects and if objects are overlapping, this implies an ordering based on distance from the viewer. Occlusion is our ability to perceive the edges of subjects in the visual field, well if this is so we must recognize the lines that make up the edges. We know that our receptive fields are particularly sensitive to lines and we know that there are specific cells in the primary visual cortex that are tuned to recognize lines at different orientations and such. Also for occlusion to be valid we must be able to pick objects from the lines, and recognize them as separate rather than one oddly shaped object. This requires higher order processing done in the temporal lobe and inferior gyrus. So occlusion is a principle that taps into many aspects of the visual system that are already occuring. Occlusion is called a non-metrical depth cue because it does not help to determine amount of distance, rather it is just an indicator that depth and distance are likely present. Size and position cues also allow our brain to assume information from just one perspective. The logical principle is instilled somewhere in us that the smaller something appears the further away it is. We recognize not just size as an indicator but the size relative to the position in the visual field. Another logical principle that seems instilled is the recognition of a particular texture gradient, or organization of objects by size. In our visual experience we experience close objects as near the bottom and center of the visual field. As objects get further away they literally move up in direction in our visual field. (if you imagine our visual field as a 2d image which is what our retina sense). We know that the higher in the visual field the further away so we make assumptions about distance based on where an object falls in the field, rather where it begins and ends. Relative height refers to what we perceive when we recognize that an object that seems shorter but is higher in the visual field is further than an object that is lower in the visual field. The book has a figure of some rabbits on page 132 that is illustrative. Aerial perspective refers to the idea that our visual system has adapted to the atmosphere of earth and can recognize distance based on the effects that air commonly has on objects that are further away. Often far objects will appear hazy, especially if they are high in altitude so this information allows our brain to assume distance as well as likelihood of looking at an angle that is increasing in altitude. Linear perspective is recognized by our brains whenever we look down a long road. This principle holds that our brains are aware that parallel lines come to a point when viewed from it's perspective. So if the brain observes lines that come to a point near the middle of the visual field it assumes that distance is likely. Motion, which is happening constantly to almost all the objects we view, yields so much information. Motion parallax is a non-pictorial cue, or a cue that is not based on a static two dimensional image. The principle at work here holds that when we are in motion, objects that are closer to us will shift position more than objects that are further away. If you think of driving in a car and looking out the window, trees in the distance seem to be moving by very slowly and trees close to the side of the road zoom by so we can barely focus on them. When we are in motion we pick up cues from how much subjects in the visual shift position and determine if these cues imply that the subjects are at great distance.
When using both eyes data collected from the fovea of each eye is compared to asses how much distance exists between the subjects in the visual field, as well as how much distance exists between the subject and the eyes themselves. The perception of three dimensionality is created by this process called stereopsis. When we focus on an object, our eyes are organized such that what we are focusing on falls on both fovea. Because this object falls on the same area of the retina of both eyes we say that it falls on corresponding retinal points. Any point of stimulation falling on the imaginary circle that runs through both eyes and the object the eyes are focused on will be represented on corresponding retinal points. This imaginary circle is called the Vieth-Muller circle. Any objects falling on this imaginary circle are represented with corresponding retinal points and are said to have zero binocular disparity. Binocular disparity refers how much difference is perceived in the position of an object when the images from both eyes are cognitively compared. Any object falling on the Vieth-Muller circle has zero binocular disparity and therefore cannot give any information of 3 dimensionality. The book describes the concept horopter, or a surface of zero disparity. It does not do that well maybe something to cover in class. Objects that do not fall on any areas of zero disparity cast their stimulation on non-corresponding retinal points. Each retina is sending different information about an object's position in the visual field, this double sensation of the object is called diplopia. When the two images projected on the retina are processed, the diplopia is analyzed. Objects that fall on non-corresponding retinal points will occupy different positions in each eye's visual field. The greater the difference in position, or the greater the binocular disparity, the more distance the brain assumes lies between that particular object and the point of focus. I will probably blog more on this topic, like I said I love it and binocular depth perception is pretty fricken complicated. I am still fuzzy about it but just would love to hear about it in class!!!!!
Things to cover in class. Binocular depth perception,
I found all the advantages of having two eyes instead of one really interesting. I found this to be interesting because I jumped to the conclusion that the visual process would be exactly the same in the unison with each other. Depth perception is defiantly enhanced by having two eyes. The reason for this is binocular disparities. Binocular disparities are differences between images in each eye. However, small, there are still differences. Binocular disparities can also provide support perception. Other things such as expanding the visual field and binocular summation both are luxuries of having to eyes. I also found it very interesting that the brain uses tricks to try to solve correspondence problems between our two eyes. Correspondence problem is “the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye” (pg. 145). I also found binocular rivalry to be very interesting. Binocular rivalry is a perceptual competition between the right and left eye.
The two things I found least interesting are corresponding retinal points and the physiological basis of stereopsis. First, I didn’t find corresponding retinal pints to be interesting because I am just not into that geometry stuff. Second, I didn’t did not find physiological basis of steropsis to be interesting because it got a little confusing. The disparities really lost me. The chapter overall was a very interesting one to me, therefore it was hard for me to pick what two things were not very interesting to me.
Two things I would like for you to go over in class are random dot stereogram and motion cues. Motion cues seem very interesting, I would love to have a better, and more educated understanding of what that’s all about!
Terms: binocular disparities, support perception, visual field, binocular summation, correspondence problems, binocular rivalry, retina points, physiological basis of stereopsis, random dot stereogram, motion cutes.
The book states having two eyes is important because it allows us to see more of the world, more depth and dimension in our vision. It seems obvious to me to state two eyes are better than one. As the book points out, most animals have been naturally selected to have two eyes and I know personally I cannot see very well when I only have one contract. It is because there is overlap; the eyes work together to perceptive our world.
There are differences between the two retinal images of the same world, or a binocular disparity. Objects that we see to the sides of our eye might not be picked up by the other. The book states that the combining of these the differences of these two images is a main way we are able see depth and dimensions of our 3D world. This is called stereopsis.
Other depth cues that rely on information from one( monocular) or both of our eyes(binocular) that help us order our world. Occlusion is a cue to relative depth when one object blocks the view of another object. You can clearly see that one object is in front of another object. It is a nonmetrical depth cue, so much as it only gives information about the relative ordering of the world, nothing about the exact information about the distance.
Size also gives us information about the geometry of the world. Knowing the familiar size or an idea about objects in our world normal size, gives us information about their position of the world,. We know that smaller is farther away this is a cue of texture gradient. Furthermore, according to relative height things that are farther away tend to sit higher in our field of vision. Thus things that are closer to us, like book next to me at the bottom is bigger, while the books at the end of the table smaller and perceptive to be farer away at the top of my visional field. Familiar size can also tell us about the relationship of things. We know our finger is not the size of a building but from a distance we know that we can block it from our vision.
Lastly, we take cues about depth from motion. Motion parallax is a depth cue that cannot be captured in a picture. The term motion parallax, according to the book, refers the information obtained from when you shift your eyes between two different images, things closer to you shift more. This makes sense because you are more likely to see motion in objects that are closer to you than objects that are far away.
Difference in two retina images or binocular disparity can be measured. If the object hits the same points or spots on each retina, or the same distances from the eye’s fovea than they are on corresponding retinal points. This image will be understood as one object. For example, if a pillar hits the fovea of each eye then it will be perceived as the same object. The more space between the corresponding points of objects will make the differences more apparent. This I found to be the most confusing. The stereoscope was used as the first way that scientist could see how the visual system treats binocular disparity as a depth cue as the images would pop out.
The physiological of depth cues and stereopsis I think is also interesting. The cells do not converge until the striate cortex, where neurons are binocular. Such cells have two similar receptive fields in both eyes focus on matching the two retina images. Some binocular neurons respond best to retinal images are on corresponding points, while others respond best when the disparity between the points is slight.
Monocular vision, also known as one eyed vision. When talking about monocular vision it is not only important but also interesting to talk about monocular depth cues. A monocular depth cue is a depth that is available even if the world is viewed with only one eye. Artist use different cues to make a picture look three dimensional even when it is only two dimensional. Every environment that we are in provides multiple depth cues. This chapter refers back to occlusion when talking about depth cues. The example given of occlusion is the picture of the triangle, square, and circle. The triangle looks like it is in the back, the square looks like it is in the middle, and the circle looks like it is in the front. Our eyes and brain make us think that the things we cannot see are complete. Seeing with only one eye doesn’t mean that you see half of what you do with two eyes. Monocular vision is when each eye is used separately. The field of vision is increased during monocular vision. most birds have monocular vision. If you do have monocular vision there are some steps you would have to take to adjust the way you live. Monocular vision will affect your peripheral vision. Although not a lot, your depth perception will be effected.
The next topic I would like to talk about is binocular vision. Binocular is vision when both eyes are used together. Having binocular vision gives you a larger field of view. The first thing to mention about binocular vision is binocular disparity. Binocular disparity is very interesting to me. Binocular disparity is the difference between images falling into your retina. This is something that I have never thought about before. Stereopsis as described by the book is the popping out in depth. The book says that stereopsis is in somehow related to binocular disparity. The reason for this is because it goes away when you close one eye. Another term involved with binocular vision is corresponding retinal points. A horopter is the location of objects whose images lie on corresponding points. The book states that if life were simple the Vieth-Muller circle wouldn’t exist. Another word for double vision is diplopia. This section of the chapter was a very confusing one but the chapter goes on to talk about disparity. There are two types of disparities, first is crossed disparity. Crossed disparity is crossed disparity means infront of the horopter. Uncrossed disparity is the second. Uncrossed disparity means behind the horopter. I did further research on binocular vision and learned about binocular summation. Binocular summation is the ability to detect objects is greater.