Superposition of edges and gratings: Interaction between central and peripheral regions

The test pattern was a bipartite field with a sharp edge (step) masked by suprathreshold sinusoidal gratings of variable spatial frequency and phase. With grating contrast increasing an increase of the step threshold contrast was found for cosine phase gratings. In addition to the above effect sine phase gratings lead to a decrease or increase of the step threshold according to the polarity of the grating. It was possible to show that the inhibitory component can be attributed to more peripheral regions of the grating, while the excitatory or inhibitory component is due to a region close to the onset of the edge. Experiments with spatial frequency adaptation showed that the inhibitory influence is selectively impaired. Dichoptic presentation of step and gratings showed an interocular transfer of the inhibitory component, while an interocular transfer of the excitatory or inhibitory component is only found for identical dichoptic stimuli. The results are discussed from the point of view of masking by structure and its interpretation by interchannel inhibition.