演題番号 : P3-h10
田野 達也 / Tatsuya Tano:1 佐々木 秀一 / Shuichi Sasaki:1 岩本 義輝 / Yoshiki Iwamoto:1 吉田 薫 / Kaoru Yoshida:1
1:筑波大院・人間総合・神経生理 / Lab Neurophysiol,Univ of Tsukuba,Tsukuba,Japan
The Muller-Lyer (ML) figure, a line with wings on its ends, is known to induce visual illusion. In a wing-in variety (a line with wings extending inward), the line appears shorter than it actually is. In a wing-out figure (with wings extending outward), it appears longer. The ML figure affects eye movements as well as visual perception. Previous studies showed that saccades along a wing-in figure are smaller than those along a wing-out figure. Some previous studies reported that the ML figure affects the evaluation of the length of a line but not the location of a line end. However, the evidence seems insufficient to rule out misevaluation of location. The present study attempts to distinguish between the two possibilities. Five human subjects participated, who all had normal or corrected-to-normal visual acuity. Eye movements were recorded with an Eyelink-II eye tracker (SR Research Ltd.). The visual stimuli, presented on a CRT monitor, consisted of a red target spot and wing-in and wing-out ML figures. The length of the horizontal shaft was 6.0 deg, and that of wings was 2.0 deg. Two ML figures, one wing-out and the other wing-in, were displayed in the upper and lower parts of the screen, or vice versa. They were vertically separated by the shaft length with the apexes vertically aligned on both sides. Subjects were instructed to make saccades to the red target spot that jumped between apexes in a clockwise direction. As expected, saccades along the shaft undershot and overshot the target in the wing-in and wing-out figures, respectively. Saccades across the vertically aligned apexes were slightly inclined and missed the target. Their endpoints were deviated inward for the target at the wing-in apexes and outward for the target at the wing-out apexes. The results may support the possibility that ML figure modifies evaluation of location of the apex, which in turn leads to misperception and changes in saccades.