Leonardo believed that sight was the most important of all the senses. His understanding of how the brain functions confirms this view.

In this profile drawing of a male head, Leonardo adheres to the conventional view that the brain possessed three inter-connected ventricles, each which facilitated a particular stage in perception.

The first, called the imprensiva, receives information gained from the senses.
This travels to the second chamber called the sensus communis, where fantasia or imagination resides along with intelletto or intellectual reason. Leonardo believed that this was the site of the human soul, as illustrated in his Study of a human skull. The sensus communis is attached to a third chamber called the memoria, where information could be stored.

Priority is given to information gained through sensory perception in Leonardo’s theory. The imagination cannot visualise such beauty as is seen by the eye. This is because the eye receives the appearance of images or objects and transmits them through the sense organs to the understanding where they are judged. Forms created in the imagination are therefore inferior; ultimately they fade and die in the memoria.

In Leonardo's words
The eye, which is the window of the soul, is the chief organ whereby the understanding can have the most complete and magnificent view of the infinite works of nature; and the ear comes second, which acquires dignity by hearing things the eye has seen.