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Paul MacNeilage, Bjorn Vlaskamp; Speed discrimination during optokinetic nystagmus: Probing transsaccadic memory of visual motion. Journal of Vision 2011;11(11):534. doi: 10.1167/11.11.534.
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© ARVO (1962-2015); The Authors (2016-present)
Optokinetic nystagmus (OKN) is a reflex of the eye that acts to stabilize moving images on the retina. It is characterized by a pursuit-like slow phase during which the eye tracks the moving image, and a saccade-like fast phase during which eye position is reset by a ballistic eye movement in the direction opposite the image motion. Around the time of saccades spatial perception is distorted and similar effects have been observed in association with the fast phase of OKN (Tozzi, Morrone, & Burr, 2007). The aim of the current study was to evaluate to what extent the saccade-like fast phase of OKN influences perception of speed during the pursuit-like slow phase. On each trial, subjects were presented with a field of moving dots and asked to follow the motion with their eyes, i.e. OKN. After 1–2 secs, the speed of the dots was instantaneously reset to a comparison speed that was either faster or slower than the original speed. After approximately 300 more ms the dots were extinguished and the subject indicated whether the dots appeared to move faster or slower. The procedure was repeated numerous times for a range of comparison speeds and psychometric functions were fit to obtain speed discrimination thresholds. There were two conditions run in separate blocks: in the fast- and slow-phase conditions the speed was reset during the fast and slow phase, respectively. Thresholds in the fast-phase condition were generally low (mean Weber fraction approx. 5%) and were most often reduced relative to those in the slow-phase condition, suggesting that the fast phase of OKN may actually facilitate speed discrimination. Assuming that the fast phase of OKN is similar to a saccade, we conclude that transsaccadic memory of speed is very good. This result contrasts sharply with degraded transsaccadic memory for spatial position.
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