CENTER/SURROUND: THE FIRST STEP IN VISUAL INFORMATION PROCESSING
As we have said, vision is information processing, not image transmission. At every stage in vision, neurons perform calculations or operations on their input signals, so that the end result is information about what is out there in the world, and how to act on it-not a picture to be looked at.
In 1953 the neuroscientist Stephen Kuffler discovered the first and most fundamental step in visual information processing. He recorded activity from retinal ganglion cells and found that he could activate the cells (make them signal) with small spots of light. This alone was not news, since it had been clear for centuries that the eye responds to light. What was surprising, though, was that small spots activated the cells better than large spots. Each ganglion cell was optimally activated by a tiny spot of light at some particular spot on the retina, its receptive field. Kuffler deduced that the reason large spots of light were ineffective was that ganglion cells were not only excited by light impinging on their receptive-field centers, but they were also inhibited by light falling on the immediately surrounding region. This organization is called center/surround.
CENTER/SURROUND CELL
This diagram represents the receptive field of a typical retinal ganglion cell, the part of visual space to which the cell responds. Such a cell is activated by light falling on a small part of the retina (pluses), and suppressed (minuses) by light falling on the surrounding region. This organization is called center/surround and is responsible for many features of our visual perception.