Democritus of Abdera (circa 460-circa 370 B.C.E.) was known as the "Laughing Philosopher" because of his commentaries on the foibles of man. Only a few fragments of his writings survive.

On sense perception:

Sight takes place by means of a physical impression.... which does not occur spontaneously in the pupil of the eye. Instead, the air in between the eye and the object is compressed and stamped by both the object and the viewer, since [atoms] are always flowing from everything.

They associated vision with certain images, identical in shape with the object, that constantly streamed, from the object and impressed themselves on the eye.

On tastes:

He defines "sweet" as something [made of atoms that are] round and moderately large; "sour," as what is large, round, polygonal, and linear; whatever is "sharp tasting," as the name implies, sharp edges...