From the late thirteenth to the early seventeenth century, the process of visual imaging was understood in the Latin West as an essentially subjective act initiated by the eye and completed by the brain. The crystalline lens took center stage in this act, its role determined by its peculiar physical and sensitive capacities. As a physical body, on the one hand, it was disposed to accept the physical impressions of light and color radiating to it from external objects. As a sensitive body, on the other hand, it was enabled by the visual spirit flowing to it from the brain to feel those impressions visually. Acting as a sentient selector of visual information, the lens transformed the brute physical impressions of light and color into visual impressions. These, in turn, gave rise to perceptual “depictions” that were passed back along the stream of visual spirits to the brain. Known in Scholastic parlance as “intentional species,” these depictions served as virtual representations of their generating objects. As such, they provided the wherewithal not only for perception, but also for conception and cognition.
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