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Jianliang Tong, Saumil S. Patel, Harold E. Bedell; Asymmetrical modulation of the temporal impulse response during smooth pursuit. Journal of Vision 2006;6(6):866. doi: 10.1167/6.6.866.
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Purpose. Recent experiments indicate that the extent of perceived motion smear is attenuated asymmetrically during smooth pursuit eye movements (Tong, et al., Vision Res. 2005). In this study, we investigated whether the asymmetrical reduction of perceived smear during pursuit is associated with an asymmetrical speeding up of the temporal impulse response function (TIRF).
Methods. The stimulus was a 10 deg patch of a vertical sinusoidal grating, presented on a 20″ monochrome monitor and viewed monocularly from 114 cm after reflection from a galvanometer mirror. On each trial, a 1 cpd stimulus was presented for 400 ms, with Gaussian temporal windowing to limit the spread of the temporal frequency spectrum. Contrast sensitivity was determined for leftward and rightward image motion at temporal frequencies between 6 and 30 Hz, during fixation and rightward pursuit at 8 deg/s. Horizontal eye position was measured on pursuit trials using IR limbal tracking. TIRFs were determined by iterative Fourier analysis to fit the temporal contrast sensitivity functions measured for each direction of target motion during fixation and pursuit.
Results. As we reported previously (VSS, 2003), the natural frequency of the TIRF is higher during smooth pursuit than fixation. Moreover, the TIRF is 10 – 15% faster for gratings that move AGAINST compared to WITH the direction of pursuit.
Conclusion. The results are consistent with the hypothesis that extra-retinal signals reduce perceived smear during pursuit, partly by increasing the speed of visual processing preferentially for one direction of image motion.
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