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Ervin Poljac, Albert Berg; Perception of the Plane of Regard. Journal of Vision 2003;3(9):494. doi: 10.1167/3.9.494.
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© ARVO (1962-2015); The Authors (2016-present)
To avoid collision with an object or to bring it to the right position on the face, one needs to estimate its position relative to the head. A visual head centric representation of the object would be convenient. When we fixate an object in space, the rotation centers of the eyes together with the object, define a plane of regard. Localisation relative to this plane might be a good starting point to judge other objects' positions relative to the head. Objects in the plane of regard are imaged on the horizontal retinal meridia of both eyes, provided the eyes do not rotate about the line of sight. According to Listing's law eye torsion depends on the fixation direction. Similarly, head-tilt evokes compensatory eye torsion. Does eye torsion cause mislocalisation of the plane of regard?
Subjects judged elevation of flashed probe points relative to their plane of regard, while fixating straight ahead, right upward, or right downward at 30 cm distance. Probe azimuth ranged from −20 to 20 degrees. The fixation point was extinguished prior to the probe's appearance while subjects maintained fixation in total darkness. If fixation failed, the trial was repeated. Although conjugate eye torsion varies by 8 degrees across these different fixation directions, the perceived elevation of eccentric probes was not biased towards the location of the horizontal retinal meridian. Similarly, the perceived plane of regard tilted by as much as the head tilt, again indicating that subjects did not solely rely on retinal cues for the plane of regard estimation. We conclude that people perceive their plane of regard correctly, which could be useful to represent the position of objects in head centric coordinates.
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