Vision depends on context. At a basic level, what you see depends on what’s around what you see. This is essential in drawing— just take a segment of one of my favorite drawings by Van Gogh.
What is it of? Dots? Boredom? Nothing?
Put back at home in the lower right corner of a drawing of a cottage garden it’s – ta da! – a pebbly path.
In Psychology 101, perception is often explained through optical illusions. For example, the Ebbinghaus illusion presents two circles, one surrounded by larger circles, the other by smaller. Although the two central circles are the same size, the one surrounded by the little circles appears larger. It’s a context effect, and it breaks my heart every time. If even simple stuff like this is warped in my mind, how can I hope to see anything truly?
The Ebbinghaus Illusion is a textbook example, but context effects in early visual processing are something we experience all of the time. Walk out of a dark theater on a summer afternoon and you will be blinded by the sun. The colors you perceive in the evening are different than the ones you perceive in the morning, as Monet captured in his series of the cathedral at Rouen. In the Ebbinghaus Illusion, you can measure the circles and verify that they are equal, revealing the truth that ought to be perceived. But what’s the true color of Monet’s cathedral? Your experience in place and time inevitably affects the information you get from your environment.
Context effects are an issue that extends beyond early visual processing into every level of perception and cognition. Working at UC Davis’ Center for Mind and Brain, I assisted with research on the relationship between visual attention and visual working memory. Experiments documented that the context of vision isn’t just visual information. It’s also experience. The things we pay attention to enter our memory. Memory, in turn, guides attention. You know what you see. You see what you know. It’s a chicken or the egg kind of thing—context effects mean there’s never a clean start.
History is full of examples of the ramifications of context effects. For example, during the 19th century cholera epidemics, physicians saw their cholera patients’ symptoms through their experience with poisons. Patients, afflicted with vomiting and diarrhea, looked like they were trying to get a poison out of their body, so physicians gave them substances to further encourage the exit of fluids. The patients nearly always died. Now, with our contemporary understanding of the disease, we see that they were killed by dehydration.
During the epidemic, one physician went against all accepted thought and gave his patients something to drink. The death rate plummeted. Thrilled, he called his colleagues to report his results. When they arrived and saw the healthy patients they said, “If these people had really had cholera, they would be dead.” They couldn’t see the cure. Their context was blinding them.
To not be blinded by context, we must become aware of it. Malcolm McCullough writes in his book Digital Ground, “‘[C]ontext’ is not the setting itself, but the engagement with it as well as the bias that setting gives to the interactions that occur within it. ‘Environment’ is the sum of all present contexts.”  To avoid being blinded by context, we must understand our environment, and the biases guiding how we are informed by it. But how?
Understanding context requires understanding our place in the world. Knowing means knowing how what we know shapes what we know. Nothing is alone. Nothing is simple. Not a fact, not a thought, not a mark.
 Sonia, Shah, Pandemic (New York, NY: Sarah Crichton Books, 2016).
 Malcolm McCullough, Digital Ground: Architecture, Pervasive Computing, and Environmental Knowing (Cambridge, MA: MIT Press, 2004), 48.