EFFECTS OF MULLER-LYER ILLUSION ON THE ACCURACY OF PRIMARY SACCADES AND SMOOTH PURSUIT EYE MOVEMENTS
The goal of the present investigation was to support or to oppose the two-visual-system (vision for perception and vision-for action) hypothesis. Since illusions might be the subject of misinterpretation and the loss of presented information, we decided to examine how Mtiller-Lyer (M-L) illusion affects accuracy of double-step saccades and smooth pursuit eye movements and compare these results with those obtained during perceptual judgment of the length of the shaft of M-L illusion. Experimental investigation revealed that the primary saccades elicited in double-step mode were mostly affected by the M-L illusion. The position errors of the primary saccades elicited in the reflexive mode were affected by 4% for wings-in illusion and by 3.6% for wings-out illusion comparing with the 0.25% and 0.1% for the saccades elicited in the voluntary mode. The position errors of complete saccades (0.14% and 0.02%) and tracking errors obtained during the smooth pursuit (0.11% and 0.05%) were negligibly small. Nevertheless, experimental results obtained during perceptual judgment of M-L illusion were substantially larger - 14% and 10%, respectively. Our experimental investigation of the accuracy of saccadic and smooth pursuit eye movements elicited to the stimulus with M-L illusion unfolded that the visuo-motor system is able to resist to the illusory stimulus and supported the two-visual-systems hypothesis. Obtained results have demonstrated that the main parameter, which plays the most important role on the precision of visuo-motor behavior, is the uncertainty of perception of the shape and the position of the illusionary stimulus.
illusion smooth pursuit eye movements double-step saccades visuo-motor system dynamic illusion evaluation