FINAL BLOG ENTRY

One of the most surprising things that I learned this semester in Perception was this concept of adaptation, particularly in the field of vision. We can fatigue certain types of cells which leads to the perception of something different. This leads to illusions, making us think we see more than what is really out there in the world. It’s another piece of evidence that confirms this statement: perception is not just objective.

We first learned about fatigue in vision when we talked about the tilt aftereffect. After fixating on slightly tilted lines, subsequent lines will seem to have a tilt in the other direction. This works if you are looking at vertical or horizontal lines. This illusion works because we have direction specific cells in our visual system. When a specific orientation is presented as a stimuli, the cells that have a preference for that orientation fire rapidly. This is the adaptation process. When we look at another set of lines, they now seem to have a tilt in the other direction. This is because we have fatigued the cells that preferred the first orientation. Now the ones that react strongly are the ones in the opposite direction.

Then we talked about the color after effect. When we look at green for a period of time, looking away causes us to see a red color. This works in reverse; it also works for blue and yellow (you see yellow after looking away from blue). The same concept works for this illusion. We have 2 chromatic channels as part of our visual system: the red-green channel and the blue-yellow channel. When you look at a red stimulus, the cells that prefer to red are being used and will soon be fatigued. Then, because the brain responds to less activity from cells that prefer red as green, we will perceive the color green.

Finally, we talked about the motion aftereffect. After seeing an image of something contracting or expanding, we will see something move in the opposite manner even if that image is static. We experienced this in class with the Buddha image. He seemed to be expanding despite the fact that it is a picture. From class, we learned that perception is mediated by comparisons between the neural responses to motion in opposite directions. So following exposure to one type of direction, we will perceive the opposite direction when we look away. Additionally, according to a study done by Jonathan Winawer, an aftereffect occurs for still photographs depicting motion. The article stated “Three experiments showed that viewing a series of static photographs with implied motion in a particular direction produced motion aftereffects in the opposite direction.” He concludes that the perception of implied motion uses the same direction specific cells that are used in real motion processing.

How cool is that? The fact that we can see things that are not really in reality is amazing. There really is more than meets the eye. When I said the concept of aftereffects was the most surprising thing I learned about this semester, I meant surprising in the sense that I have never thought about this before. I must have experienced these illusions before, but it has never crossed my mind to understand how or why it works. It’s mind boggling how complex our senses really are when it doesn’t take more than us opening our eyes for vision to work. Since it is so automatic, I think we really take our senses for granted.

Akinetopsia

This week, we talked about motion and how we perceive motion. We learned about a woman who had a deficiency in this perceiving ability. It baffled me. Once again, I can’t imagine living life this way. It’s as if she was using a flip book as she walked through life.

Any avid reader of my blog entries will notice that the most interesting topics to me are conditions where there is a deficiency in “normal” perception. I must qualify that statement; to normalize perception is useless because we know that there is a subjective component to perception. However, I mean to say that conditions that result in atypical sensations are very interesting to me.

But I digress. Let’s go back to talking about patient L.M. She suffered a stroke and lost her ability to perceive motion, a condition called akinetopsia. As we learned in class, motion is its own sensation and is not an extrapolation over time or space. Her other visual systems functioned normally. She could identify objects, see colors, etc. Things like crossing the street scared her, as it should. But relatively medial tasks like filling a cup with water or listening to someone talk were nearly impossible without some type of trouble. She could not see when the water level of a cup move so she did not know when to stop pouring. She would get freaked out by hearing someone talk without seeing their lips move.

Because the condition resulted from her stroke, it means that she had normal visual functioning before her stroke. This also means that she experienced something very different than what she was used to which could cause potential mental disturbance. I know if I suddenly developed this condition, I too would be very scared and freaked out by it. I do not even know how I could cope.

What is very unique about this situation is that all her other senses are intact. Like I mentioned before, her hearing was not disturbed so she could hear things that did not match up with what images she saw in her head. What I wonder is whether or not she could still sense biological motion. If she suffered a stroke and only certain areas of the brain were affected, was the superior temporal sulcus, the area associated with biological motion, affected as well? If not, maybe she could still perceive biological motion. These questions will be left unanswered as she was the only documented case with this condition and she is deceased.

Color blindness is a subject near and dear to my heart. No, I am not color blind and I proved that to myself in class! What I mean is that my oldest sister, Karen, has this condition yet fails to acknowledge it! It reinforces the idea that perception has a subjective spin on it. To her, she is right; that blue car is indeed green and everyone else is color blind. What a silly girl.

I always knew my sister was a special gal. She is part of the 0.05% of females in the U.S. population who have some type of color deficiency. Only she has yet to admit it. Being the good sister that I am, I have decided to diagnose her. Of course this is only a very rudimentary evaluation. As I have mentioned before, she has a problem distinguishing between greens and blues. It seems likely that she has tritanomly, the rarest form of cone deficiency. Tritanomly means there is malfunctioning in the S cones which equals difficulty in distinguishing between blue and green.

Because color perception involves the actual wavelength that an object reflects AND the ratio of activity in our cones, people with deficiencies in the proper functioning of any of the cone types will have some type of color perception that is vastly different from people with normal functioning cones. In my sister’s case, if a certain object reflects the color green, the ratio of activity in her cones would indicate the color blue.

We can determine the objective color of an object by measuring the wavelength that it reflects. With experiments, we can determine whether or not a person perceives this color. Through matching tests where subjects turn a knob to match the color perfectly and through tests like the Ishihara, we can determine whether or not someone has deficiencies in their cones.

It’s not that my sister cannot completely see color. It’s not like she only sees gray when she looks at the color green. She only perceives it differently than people with normal functioning cones. In a website about tritanopias, the author mentions the fact that most people with this condition fail to even acknowledge it’s existence compared to the deuteranopias and protanopias. Because a big part of driving depends on differentiating between a red stop and a green go, when one has difficulties discerning these two colors, it’s very noticeable. But my sister can go through her entire life believing that the car is blue despite the rest of the family telling her it’s green.

It is very difficult to determine if someone else is perceiving the world in the same way as us. That is the reason why some people do not even know they have color blindness until they learn about the condition. There are numerous tests that one can take to determine color blindness, so we have these tools to help us in the quest. We can simulate how our cones are supposed to work, but we will never really know if something as subjective as color perception is the same in other people.

I hope no one will disagree with the fact that the human brain is complex. Every second, millions of processes are taking place. Some we are aware of and some we give no thought to.  If we did not have organization or partitioning of responsibilities, I’m afraid our heads would blow up! All jokes aside, the brain needs to be organized in a way that allows it to operate at maximum efficiency. The reason why I think the cortex has so many areas devoted to processing different types of visual information is for efficiency and because of evolution.

Our cortex is structured so that different inputs from the visual world get sent to different parts of it. Visual illusions are processed separately from simple visual information. This partitioning of responsibilities allows the brain to classify information from the visual world. I believe this allows it to be more efficient and faster in processing. A graduate student from MIT, Bhavin Sheth, calls the visual system an orchestra, “where clusters of cells in different parts of the brain cooperate to process different components of visual information such as vertical or horizontal orientation, color, size, shape, movement, and distinctions between overlapping objects.”

I also believe that our cortex gives such great areas to visual processing because of evolution. It is very important to our survival to be able to have “hunters’ eyes.” In order to be the fittest, we must be the strongest and that happens by being the hunter. Since our visual system has allowed us to evolve the way we have, it means that the cortex is structured to enable us to be the best adapted in our environment.

Even though we have areas devoted to processing different types of visual information, it does not negate the fact that many of the areas are used in an overlapping manner. In 1996, MIT researchers discovered that areas used in processing simple visual information were also used in processing complex information like optical illusions. Research done on animals showed that an area of the brain previously thought to process only simple information was active when shown an optical illusion. This debunked the previous notion that the areas of the cortex worked in a hierarchy; instead it was believed that they work cooperatively.

As complex as the brain may be, we are slowly finding out more and more about it. Let’s just say it’s a fascinating time to be in neurology as well as Perception…