VISUAL-EVOKED POTENTIALS TO GEOMETRIC FORMS - EFFECTS OF SPATIAL ORIENTATION

Five outlined geometric figures of equal contour length were presented monocularly below the fixation point (FP); an upright equilateral tri angle (upright triangle), an inverted equilateral triangle (inverted t riangle), an upright square (square), a 45 degrees-tilted square (diam ond) and a circle. The angular separation between FP and the top of th e figures was held constant. Transient visual evoked potentials (VEPs) were recorded monopolarly from inion, 4, 7, 10 cm above it (I, I4, I7 , I10) and Cz for ten subjects. The grand-averaged subtracted waves we re obtained between the figure and blank (control) conditions. N1 (mea n peak latency: 155 ms) and P2 (240 ms) waves were identified. ANOVAs were conducted for the latency and amplitude values. Main results were as follows: On the N1 amplitude at 14 and I, the upright triangle, in verted triangle and diamond figures evoked significantly larger respon ses than did the square and the circle. However, no significant differ ence was found among the former three figures. These findings on the N 1 amplitude suggest that the effect of a triangle is orientation-free and that of a square is orientation-bound.