Stereo vision without the ventral stream
Because the eyes are set apart horizontally in the head, they receive two different views of the world. Our brain can use these small binocular disparities to deduce the distance of objects, and produce a rich perception of 3D stereo depth. It is still not clear how or where in the brain this occurs. Visual information is processed in two main streams, known as ventral & dorsal from their anatomical location. The ventral stream is thought to support object recognition, whereas the dorsal stream provides the precise information on physical location which we need for motor actions. Both streams contain information about stereo disparities, and little is known about the different ways in which they may process and use it. Recently, we tried to gain insight into this by investigating stereo vision in a patient who has suffered severe damage to her ventral stream. Despite her brain damage, she has generally good stereo vision. However, we found that her lesion had removed her ability to perceive tiny depth differences between adjacent surfaces, which is characteristic of stereo vision in healthy controls.