Visual grouping without low spatial frequencies

Gestalt psychologists have stressed the perceptual importance of grouping. On the basis of multichannel theory of early visual processing, grouping has been attributed to the operation of channels tuned to low spatial frequencies. If this explanation is correct and sufficient, grouping should not occur when looking at highpass filtered images, because they do not excite low spatial frequency channels. However this paper brings evidence that visual grouping also occurs in such a situation. Hence, a more comprehensive explanation of visual grouping is needed.