How do sine-wave grating tests identify nonclassical receptive fields in the visual system?

To identify nonclassical receptive fields in the visual system, researchers use sine-wave grating stimuli to observe how responses change when the stimulus extends beyond the classical receptive field.

While the classical receptive field is defined by the region where stimuli alone can elicit a change in a neuron's spiking activity, the nonclassical receptive field—often called the modulatory or silent surround—consists of regions that cannot evoke responses on their own but can modulate responses driven by the central portion of the field.1

To identify these regions, investigators vary the size of sine-wave gratings centered over the classical receptive field. By comparing the neuron's response to stimuli that are smaller than the classical receptive field against those that exceed it, researchers can determine the extent of the summation area (or summation field). Typically, responses summate over a region larger than the classical receptive field, and the dimensions of this area are often found to be greater when the stimulus contrast is low.1