So we are developing new strategies to decipher the responses to natural scenes. As well as exploring the functions of single areas, Van Essen is studying general principles of how information flows through the visual system. Hierarchies in the visual system Hubel and Wiesel initially thought information from the retina of the eye flowed through the brain in one direction, like a signal passing from a camera to a TV set. He compares this arrangement with a government agency in which employees collect information, process it and send it to a department head. Summaries eventually may reach the director, but the director also influences the data flow by asking employees to focus on certain topics.
Visual attention offers a dramatic example of such a feedback loop in the visual system.
For example, it allows us to look into someone's eyes and ignore other details of the face or other nearby objects. This strategy saves the brain from processing all of the megabytes of visual information that pass down the optic nerve each second. Postdoctoral fellow C. Edward Connor, Ph.D., discovered that paying attention to an object does not simply increase or decrease the responses of a given neuron. Testing a model originally developed by Anderson, he and Van Essen found that the part of an image to which a particular neuron can respond shifts as attention moves from one region of the image to another. The researchers now are refining their original model to obtain better quantitative agreements with these new experimental data.