An Eye-Movement Study On The Mechanism For Horizontal-Vertical Illusion

An eye tracking method was used to explore the mechanism for horizontal-vertical illusion with an eyelink II eye tracker.In experientl, a variable cue point in the dividing line was introduced to investigate that whether horizontal-vertical illusion would be diminished or vanish by changing the eyes tendency of scanning upward in the condition of not restricting time to observe. Meanwhile, as other two variables, visual angle and rotated angle would be examined how to influence the amount of horizontal-vertical illusion. According to the results from eye movements and judgments, it could be concluded that:(1)no matter the subjects claimed that the cue point would effect their judgments or not, the cue point always had an influence on their eye movements and their judgments;(2) the eye movements were different in different rotated angles, but the outcomes of judgments were not, which denied the hypothesis that the eyes tendency of scanning upward resulted in horizontal-vertical illusion;(3)the results from judgments were not different between the two visual angles, but the amount of overestimation was smaller in the visual angle of2degree than in the visual angle of4degree when there was a cue point, it might be related to the central fovea;(4)when the rotated angle of a stimulus was0°and180°, the amount of overestimation was least, it might be attention shift to the vertical line because of the cue point.In experiment2, time to observe was restricted by quick appearance, three hypothesizes were investigated:(1) whether the amount of overestimation decreased under the circumstance of cue point through the change of eye movements;(2) whether the central fovea was related to the amount of overestimation;(3) whether attention shift to the vertical line because of the cue point decreased the amount of overestimation. Experiment2proved the three hypothesizes, which showed that horizontal-vertical illusion was influenced both by sensation and by cognition:sensation was about that the closer from the central fovea, the less amount of overestimation would be; cognition was about that attention shift to the vertical line by changing eye movements would decrease the amount of overestimation.