Manipulation of integration mechanisms under identical visual angle

The coherent processing of our environment requires the integration of local elements into a global gestalt. Among a number of principles that have been suggested by Gestalt psychologists to facilitate grouping mechanisms size and proximity appeared to be powerful features. At the present stage, it remains unclear if the integration of local elements into a global gestalt can be manipulated independently from its projection to the retina. To answer this question, we took advantage of the well known illusion that an object located far from an observer is perceived larger compared to the same object located at short distances although both objects are presented under identical visual angles (e.g. 'Ponzo' illusion). If grouping mechanisms can be manipulated independently from their retinal projections, lower performance should be expected for conditions, in which the global object is located far from the observer due to its larger perception. In detail, we placed arrays of Kanizsa triangles in a modified version of the 'Ponzo' illusion at a 'close distance' and a 'far distance'. Subjects were instructed to indicate the position of the Kanizsa triangle. The results indicated that performance was lower for the 'far distance' compared to the 'close distance'. These findings suggest the integration of local elements into a global gestalt can be manipulated independently of the retinal projection and also depends on the visual context.