Figure 1.2: Descartes’ depiction of how the soul receives information through the eyes Descartes believed that the human soul is housed in the pineal gland, depicted here as the tear-shaped structure in the center of the head. In describing this figure, Descartes (1637/1972) suggested that light from the arrow enters the eyes and opens pores in structures that we now know as the optic nerves. Fluid flows from the eyes through the opened pores, causing movement in the pineal gland, which, in Descartes’ words, “renders the idea” of the arrow to the soul.

Universal Images Group/Getty Images