In the article “The autonomy of the visual systems and the modularity of conscious vision” by Zeki and Bartels, the authors seek to hypothesize and explain how the visual system in humans is autonomic and modular through evidence presented by various scientific studies, and concluding that these contribute to the modularity of the conscious vision. I will attempt to present and discuss the four main points that the authors believe allow for their hypothesis to be posited.
The first of the four points the authors attempt to build is that there are many visual processing systems in the brain which are spatially distributed and parallel; the point being that the visual brain is modular. There are several areas of the visual brain which consist of different specializations. Existing in the primary cortex, the V1 region is central to the visual brain; it receives input from the retina through the lateral geniculate nucleus and sends out parallel specialized signals to the other areas of the visual brain surrounding it. The other areas specialize in the different attributes of the visual scene such as motion and color. Specialized cells in regions V1, V2, V4, and V5 are generally accepted in the scientific community as being involved in multistage processing systems of motion and color. Particularly, there are specialized areas surrounding V5 that are involved in biological motion, rotary motion, and optical motion. Through the presentation of such scientific evidence, the authors believe the visual brain system being modular can be assumed correctly.
The second point that there exists a temporal asynchrony in visual perception, which they believe verifies that visual perception is also modular. With the visual brain being modular it is curious exactly how these spatially distributed parallel processing systems work to present to the human being the unitary visual image of the world. There are three alternative hypotheses presented on the subject. One, the systems terminate their processes at the same time. Two, the systems report the conclusions of their various operations to one central integrating area in a convergent method. Three, the various systems have a special type of communication that leads to an integrated perception of the visual image. The authors state that there is no scientific proof in anatomical experiments of the existence of a single area that receives input from the various specialized areas, thus rejecting the second hypothesis. Therefore the hypothesis posited by the authors is that of juxta-convergence, which is that the inputs from the several specialized areas do not go to a single central area and when they do project to a higher one, they maintain their own territory within it.
Also, there is evidence in psychophysical experiments demonstrating a temporal difference in the completion of tasks among the different processing systems; therefore the first hypothesis is rejected. Such evidence suggests a temporal asynchrony in visual perception, by which the authors suggest a mutual integration of the activity of the several processing systems is not necessary in order to create the visual image perceived; thus, the processing systems are perceptual systems and can be called processing-perceptual systems. Furthermore, the evidence of temporal asynchrony in visual perception also suggests that the brain does not combine results of operations from the different processing systems in real time. All of the evidence above leads to the conclusion that visual perception is also modular.
The autonomy of the visual processing systems, the third point, is a simple extrapolation based on the evidence given in points one and two. Since evidence suggests an absence of a central area where all of the specialized processes would project and a temporal asynchrony in visual perception exists, a central integrating mechanism is not necessary for visual perception. Human studies demonstrate how the several processing-perceptual systems are capable of functioning fairly autonomously. An example of this evidence is that of a person with damage to their colour centre is able to perceive motion normally, and similarly vice-versa.
In the fourth point the authors suggest there is a conscious correlate of activity in the individual processing-perceptual systems. They do so through evidence of several scientific cases, which show that subdivisions of visual attributes pathways’ are able to function relatively autonomously with activity that has a conscious correlate. One such example is the case of carbon monoxide patients who have lost the ability to see form, motion, and depth, but can sometimes retain the ability to see in color. These patients have a conscious experience of colors. There are other cases presented which all lead to the idea that activity in a certain region or even subdivision of the visual brain has a conscious correlate, essentially meaning that even if the person cannot detect motion but there is activity in the area of the brain that detects it, the person will have a conscious experience of seeing motion.
Altogether, the authors suggest that with the evidence for the four points aforementioned it is not necessary for the brain or visual brain of the human to be healthy in order for there to be a conscious experience of a specific visual attribute. Therefore, they posit, it could be highly possible for many consciousnesses to be reflecting activity in the various processing-perceptual systems of the visual brain. Thus, suggesting that the visual consciousness may also be modular, which would reflect the similar make up of the processing-perceptual system. Lastly, this all means, it must be the mini-consciousnesses that are active in each level of each processing-perceptual that must be bound in order to create the integrated image in the brain.
All in all, the evidence presented by the authors is convincing for the above-mentioned hypothesis to be worthy of exploration. Though, it appears to me to be academically interesting that most of the sources listed for research by the authors’ in majority of cases includes Zeki him/her self. But, since I cannot be a judge of the research performed or cited by the authors’, and in taking the arguments and evidence listed in the paper, it seems the authors’ hypothesis posited must be taken seriously. Such evidence suggests an interestingly new idea that the brain is not just one thing integrating many processes, rather there are existing many individual perceptual processes that create the “one” experience.
Through the process of this paper, I have presented the four main points posited by the authors for the reliability of their concluding hypothesis. I have shown how each point builds on the next in presenting the visual brain, the visual processing-perceptual systems, and finally the visual consciousness as all modular. Finally, it has been shown how the modularity of the whole system suggests that the binding of activity in each visual processing-perceptual system must really be the binding of the consciousnesses created by each, and whose binding creates the integrated image we see of the world.