Action Ontologies, Computer Ontologies-The Metaculus Journal

The mystery of perception

Out in the universe, there are merely atoms¹ and the void. On the table in front of you, there’s a ripe tomato. Inside your skull is a brain, a collection of neurons that have no direct access to either atoms or tomatoes — only the electrochemical state of some other neurons. And yet your brain is able to perceive a tomato and various qualities of it: red, round, three-dimensional, real.

On the common how-it-seems view of perception, there is no particular mystery to this. In this view, light from the tomato hits your eyes and is decoded “bottom-up” in your brain into simple features such as color, shape, and size, which are then combined into complex perceptions such as “tomato.” This view is intuitively appealing: Whenever we perceive a tomato we find the actual tomato there; thus we believe the tomato to be the sole and sufficient cause of the perception.

A closer look begins to challenge this intuition. You may see a tomato up close or far away, at different angles, partially obscured, in dim light, etc. The perception of it as being red, round, and a few inches across doesn’t change even though the light hitting your retina is completely different in each case: different angles of your visual field, different wavelengths, etc.

Take color for example. Naively, the perception of color is the detection of wavelengths of light, and yet you perceive the same color from green light (530 nm) as you do from a mix of blue (470 nm) and yellow (570 nm). A white piece of paper will appear white in your perception even though it actually reflects the wavelengths of the light around it: blue under a clear sky, green if held close to grass, orange by candle light. The strawberries in the image below appear red even though there isn’t a single red-hued pixel in it. Wherever the perception of color is coming from, it is certainly not the mere bottom-up decoding of light wavelengths.