Ruminating on Visual Perception and Optical Illusions

“Within days I could distinguish letters and my vision became that of an eagle–I can see a worm wriggling a block away. The sharpness of focus is incredible. BUT–I AM COMPLETELY COLORBLIND.”-Mr. I

This week’s reading returned yet again to the case of the colorblind painter and provided more insight into the reasons behind his dramatic shift in vision and perception. Livingstone explains that the color part of visual perception has significantly lower acuity than other parts. Meaning that because Mr. I was not using the color part, his vision was more accurate. Livingstone also divided visual perception into two subsystems, the Where system, which comprises motion perception, depth perception, spatial organization and figure/ground segregation and is colorblind, fast, has low acuity and is sensitive to high contrast, from the What system with consists of object recognition, face recognition, and color perception and is color selective, slow, has higher acuity and is sensitive to perceiving lower contrast. As hard as it was to remember which functions related to which system this was a useful way of breaking down the whole process of visual perception. Mr. I seems to use mostly his Where system and struggle more with his What system. I was not clear however, which specific regions of the brain these two systems were located. Livingstone says that the Where system is in higher visual areas while the What system is in the midbrain, but from this information I could not confidently determine which system operated in V4, which was compromised in Mr. I.

Livingstone addresses the pathway of vision from light entering the eye and being recepted by the retinal ganglion cells to the journey it takes within the brain. We covered some of this material previously in class, but Livingstone goes into detail about the different types of perception of each ganglion cell. I was particularly interested in the way the center/surround cells worked. At first it was a little difficult to understand how it worked with the outside inhibitory inputs and the excitatory inputs but the diagrams made it clearer and the optical illusion of the white lines and black squares helped to illustrate this for me. It was really neat to learn that the grey dots appear because the white in the surround part of the center/surround cells suppresses the white of the center. The visual illusions that Livingstone explains are fun and interesting to understand. I was shocked as to how much center/surround cells are at work in these optical illusions. The illustration of the newspaper also helped illustrate how these cells work and was very surprising and hard to believe. It is amazing how colors and shades play off of one another. The white of the paper made the grey of the letters look so much darker than they really were. I had to cover up the white with my fingers to perceive the color on its own. This made me think about paintings and how playing colors off of each other is an important aspect of painting and color usage. It also must be very difficult and require a lot of experimentation to know exactly what colors to mix to achieve the desired effects. Livingstone, takes her discussion in this direction as well when she addresses edges and equiluminance.

As I read Livingstone I really became overwhelmed by the number of factors at play in visual perception; light and contrast, context and distance all play important roles. For example, the equiluminant image by Anuszkiewicz was vibrating so much when I was doing the reading that it was making it incredibly difficult for me to read the adjacent text, I actually tried to cover up the image so that my eyes would stop seeing the vibrations. Yet, today as I write this post and am in dim daylight the image barely vibrates. Also depending on whether I look at it using the center or periphery of my vision the picture becomes more or less pulsating.

Solso also explained visual perception from the eye to the brain, but he also ruminated on larger questions and concepts, which I found interesting and expansive to my thinking about visual perception. He poses questions, which reminded me of some that came up in last week’s posts, like for example, what does blue look like to you and how is it different from the blue that I see? Although he did not pose this exact question he did pause to comment on the undeniable difference of individual visual perception, and the fact that we all have different brains and therefore perceive things uniquely. I thought it was also interesting when he explained that humans only have color vision in the 380-780nm range, because it evolved from needing to discern ripe fruits in the red-green range.

Another aspect of the Solso reading that struck me was the experiment he mentioned that examined parallel processing. Solso argues that parallel processing is what enables us to process information and make sense of it at such a high speed. His experiment made it possible to quantify how long it takes for someone to perceive the color red and evaluate if the color was associated to the word blood for example. This experiment in effect, calculated the range of time that it takes for us to react to stimuli and make implicit associations. This is such an isolated exercise though, when one considers how frequently we use these sorts of neural pathways and perform this task on a day to day basis or to observe a Monet painting for example, it is staggering how fast and how much our brain is perceiving!