Each subject was presented with four types of visual stimuli consisting of white isosceles triangles pointing in either the up, down, right, or left direction (see Figure 1). The stimuli were presented for 100 ms at the center of a computer screen against a dark background and subtended a visual angle of approximately 1°. The minimum response time was set at 100 ms from stimulus onset so that any faster responses would be considered premature, and would not be counted.
