What is the discussion mainly about? According to the professor, what did nineteenth-century painters consider to be a weakness

Listen to part of a discussion in an art history class. (P = Professor, S = Student)
P: So, we just got started with the French painter Paul Cezanne in our last class. He created most of his paintings in the late 19th century, although in many ways, his work is a culmination of the impressionist movement that began several decades earlier, the movement that was spurred, in part, by the growing popularity of photography.
S: But, didn’t artists, painters, feel threatened by photography?
P: They did. And that’s one of the reasons painters of the mid to late 19th century worked so hard to distinguish their paintings from the types of images that were captured in photographs. Here is one argument they used: they argued that the camera could only capture a single moment in time, but for them, that wasn’t how people actually perceive reality. "Our perception of reality is not a snapshot. It’s formed over time." they’d say. So, the techniques these painters used to suggest the passing of time moved away from the conventional techniques of realistic representation. You know, sharp details, sharp outlines. Outlines of objects in their paintings became increasingly blurred and they experimented with color to create mood. That painting titled Impression, Sunrise that we discussed a few classes ago was a good example. It is the one with the harbor scene, where there was a sense of time passing of the day just from the awakening. The colors ran into one another. There were no real distinctions between objects. The viewer got a sense of the play of light, of surfaces, shimmering. This blurring of outlines became the signature of this new style of painting. David?
S: This kind reminds me of something I read in a book recently about Cezanne and the blurring of the outlines and the process of sight. I think it was…
P: Urn, I know which book you are talking about and I’m not sure I… though it does certainly fit in with what we are talking about. Let me explain a bit about the book to the class. Now, remember what I said about the impressionist movement leading up to Cezanne? Well, Cezanne took the technique of blurring outlines even further. His paintings, particularly the later ones, lack boundaries. They are more abstract. They consist of patches of color that blend into one another and you can hardly tell what the objects are. Now, the author of the book that David’s talking about proposed that there is a connection between Cezanne’s style and the way our visual perception works in general. Modern neural science tells us that visual perception is basically a two-stage process. Information at the human eyes initially transmitting to the brain is this pretty disorganized bunch of lines and patches of color. That’s the first stage. But in the next stage, the brain processes this blurred and somewhat chaotic image to create the final picture of sharp outlines and distinct objects. This, of course, all happens automatically and we are only aware of the final result. But this book argued that Cezanne somehow intuited that before the final sharp images formed, there is this stage where colors and lines are blurred and that’s what he represented in his paintings. Mind you, he supposedly did this decades before scientists actually understood this process.
S: So Cezanne just gives us the initial chaotic impression and it’s up to our brains to make meaning out of what our eyes see.
P: Right, that’s what the book argues. Cezanne somehow understood that that’s how our vision worked.
S: So Cezanne with this abstract style is simply forcing us to go through the same process of making sense of what we see as a… as the process that the brain goes through to make sense of the information it receives from the eyes. It seems like a pretty strong case to me.
P: Well, you can certainly make the argument, but to me, it’s a stretch. You see, this two-stage process happens automatically in our brains. I mean, how could Cezanne be aware of this. I think it’s simply the case of Cezanne just continuing the tradition of this new painting style that did away with outlines and experimenting with it to see how far he can take it and what kind of visual experience it would give the viewer. To me, that doesn’t make him a neural scientist.