Abstract
The problem of perceptual organization was studied by Wertheimer in terms of grouping by showing how elements in the visual field ‘go together’ to form an integrated, holistic percept according to some general well-known principles. Grouping per se does not make any prediction about shape. The role of the gestalt principles is to define the rules of “what is or stay with what” i.e. the grouping and not the shape. The notion of ‘whole’ due to grouping is phenomenally different from the one due to shape. The form of grouping represents the groups of elements that assume the role of “parts” within a holistic percept. The form of shape is instead the result of a global perceptual process emerging parallel to or after the form of grouping and giving to the whole a unitary form mostly along the boundary contours. This suggests that grouping and shape formation can be considered as two complementary integrated processes of perceptual organization. The main purposes of this work are (i) to study the relationship between grouping and shape perception, (ii) to demonstrate that the form of grouping can influence the form of shape, and (iii) to demonstrate that the directional symmetry is a second order organization that polarizes the perception of the shape and that represents the basic principle of shape formation. Psychophysical experiments under motion conditions revealed several new shape illusions due to grouping and depending on the directional symmetry.
Supported by Fondo d'Ateneo ex 60% (to BP).