David Hubel and Torsten Wiesel recorded from neurons in the visual cortex of cats and mapped out their receptive fields. They found many neurons were excited by particular patterns of light or darkness, patterns such as dots, circles and bars. They also found neurons that were sensitive to shape orientation and movement. In this video they project these patterns of light onto a screen placed in front of the animal while recording from neurons in the visual cortex. The popping clicking sounds you hear correspond to electrical activity from these recorded nerve cells played over an audio monitor. (less info)