The Zöllner illusion consists in the perception of tilted segments seen against a texture of obliques, although, physically, the segments are perfectly horizontal or vertical. Two explanations of the illusion are proposed. The illusion is due 1) to the tendency of the visual system to overestimate acute angles or 2) to the assimilation of the orientation of horizontal or vertical segments to that of the nearest principal axis of the background texture. Three different kinds of stimuli were used. The first stimulus was a horizontal segment intersecting one oblique and the apparent slope of the segment was varied by changing the physical slope of the oblique. Participants were asked to judge the apparent slope of the segment by using a numerical scale. The second stimulus was a texture of obliques an participants rated the apparent slope of the whole texture. The third stimulus was a version of the Zöllner illusion composed of many short obliques intersecting a horizontal segment. Participants rated the apparent slope of the segment. By comparing these last ratings with those obtained with the two previous stimuli, it resulted that the apparent slope of the horizontal segment was due to the overestimation of acute angles rather than to the assimilation of orientation.
The role of the background texture in the Zöllner illusion
TOMMASI, Marco
2000-01-01
Abstract
The Zöllner illusion consists in the perception of tilted segments seen against a texture of obliques, although, physically, the segments are perfectly horizontal or vertical. Two explanations of the illusion are proposed. The illusion is due 1) to the tendency of the visual system to overestimate acute angles or 2) to the assimilation of the orientation of horizontal or vertical segments to that of the nearest principal axis of the background texture. Three different kinds of stimuli were used. The first stimulus was a horizontal segment intersecting one oblique and the apparent slope of the segment was varied by changing the physical slope of the oblique. Participants were asked to judge the apparent slope of the segment by using a numerical scale. The second stimulus was a texture of obliques an participants rated the apparent slope of the whole texture. The third stimulus was a version of the Zöllner illusion composed of many short obliques intersecting a horizontal segment. Participants rated the apparent slope of the segment. By comparing these last ratings with those obtained with the two previous stimuli, it resulted that the apparent slope of the horizontal segment was due to the overestimation of acute angles rather than to the assimilation of orientation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
