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U. Sverkersten, G. Öqvist Seimyr, T. Pansell, S. Abdi, J. Ygge; The Effect of Amplitude and Interval on Ocular Torsion When Viewing Rotating Images. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2876.
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© ARVO (1962-2015); The Authors (2016-present)
When an image containing spatial information is tilted, it induces more compensatory ocular torsion than an image without spatial information (Pansell, Sverkersten & Ygge, 2006). The aim of the present study was to investigate the effect of amplitude (of image rotation) and interval (image rotation frequency) on visually induced ocular torsion.
Ocular torsion was recorded in five healthy individuals using a head mounted video oculography system (Chronos vision, Germany). The stimulus consisted of an image showing a city scene rich in spatial orientation cues. Centered on the image was a fixation point which the subject was instructed to look at. The stimulus was displayed on a computer screen (1600x1200 @ 60Hz) at a distance of 50 cm. After ten seconds, the image started to rotate (clockwise) around the fixation point in steps of 3.75°, 7.5° or 15° at intervals of 1.5, 3 or 9 seconds. The image continued to rotate in steps for 60 seconds. The rotations had a smooth acceleration and deceleration phase and lasted one second. All subjects viewed all combinations of amplitudes and intervals in a randomized order. Between each of the nine conditions there was a washout period when nothing was displayed on the screen for 30 seconds.
An immediate transitory torsional response was found for each stimulus rotation. The 15 degree amplitude induced a larger transient response (2.40± 0.16 deg) compared to the 7.5-degree (1.8±0.19 deg) and the 3.75-degree (1.38±0.12 deg) rotations. In the tests with short time intervals, the torsional position was accumulated over time, shifting the torsional position in the same direction as the stimuli (maximum 5 deg). In the tests with longer time intervals the torsional position returned towards the initial reference position before the next stimuli took appeared.
A larger stepwise rotation induced a larger torsional response. The time interval between rotations had little influence on the transient torsional response. However, a short time interval induced a shift of the torsional position, something which was not seen at longer time intervals.
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