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Ulrika Sverkersten, Jan Ygge, Gustav Seimyr Öqvist, Tony Pansell; Ocular Torsion In Response To A Visual Rotatory Step-ramp Paradigm. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4701.
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© ARVO (1962-2015); The Authors (2016-present)
Compensatory ocular torsion has been found in response to both static tilted visual stimuli and in response to rotating visual stimuli. The purpose was to investigate the response to conflicting visual stimulation and to conclude if the brain prefers to compensate for image motion or image position.
Eye movements were recorded using a 3-D video oculography system. The visual scene was an image displaying a room. Each test person performed two tests. Each test started with displaying the scene in straight up position (0-position). i) In the step-ramp paradigm the 0-position scene was removed and at the same time a similar scene was displayed in 30-degree tilted position (i.e. step). The stimuli started immediately to rotate in opposite direction to the tilt direction with a constant velocity (i.e. ramp; 1.5°/sec) back to the 0-position. ii) In the ramp-step paradigm the scene started to rotate with a constant velocity (1.5°/sec) from 0 to 30 degree position (i.e. ramp). When reaching the 30-degree position the scene was removed and at the same time a similar scene was displayed in the 0-position (i.e. step). The subjects were instructed to keep fixation in the center of the scene.
There is a torsional response to both test conditions (step and ramp). Starting with a step the torsional response is immediate and in the same direction as the step despite the conflicting stimuli rotation in opposite direction.Starting with a ramp the torsional response follows the scene rotation. The conflicting step in opposite direction to the ramp event was ignored.
The result speaks in favor of two separate motion sensor mechanisms. While the ramp seems to trigger 1st order motion sensors the step seems to trigger 3rd order motion sensors (i.e. feature tracking). 1st order sensors cancel out the response from 3rd order motion sensors in the ramp paradigm while 3rd order motion sensors cancel out 1st order motion sensors in the step paradigm.
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