Center-of-mass alterations and visual illusion of extent.

In the present communication, we have developed a computational model related to the conception of positional coding via centers-of-masses (centroids) of the objects' luminance distributions. The model predictions have been tested by the results of our psychophysical study of geometrical illusion of extent evoked by a modified Brentano figure consisting of three separate spots clusters. In experiments, the centroids of the clusters were manipulated by varying the positions of additional non-target spots flanking the stimulus terminators. A good correspondence between the model predictions and the illusion magnitude changes provided convincing evidences in favor of "centroid" explanation of origin of the illusion investigated.