The Effects of the Fixation Point and Binocular Disparity on the Panum Pattern

The Panum pattern is a case of depth perception in which one of the human eyes sees two lines, and the other only one line; the position of this line is located in correspondence to the previous two, such as Fig. 1. When the two half-images are united, a different depth of the two lines can be perceived. Werner (1937) used the thread apparatus to investigate the Panum pattern and explained the different direction of depth in terms of temporal and nasal displacements. According to his explanations, the joint half-image will be in front of or behind the isolated one depending on the position in which the single line (a2) is initially located in the retina area. If the single line falls between the two lines in the binocular zcne, the displacement will be nasal and the joint half-image will be perceived in front of the isolated one. If the single line falls outside, the other two, the displacement will be temporal and the joint one will be perceived behind. In his experiment, the single line was located between the two lines. Our interest here is to investigate the effects when it is located outside the two lines.