The grayscale stimuli were presented on a 20-inch computer monitor with a resolution of 1024 × 768 pixels. The height of the stimuli was 9.5 cm on the screen. The target was an asterisk measuring 0.5 cm on the screen. As the participants were seated approximately 57 cm from the computer screen, the stimulus and asterisk measured 9.5 and 0.5 degrees of visual angle, respectively. The stimulus presentation and data collection were controlled by DMDX running on an Inspiron laptop PC and connected to the monitor. A response box was used to collect responses, and was specially constructed to be compatible with the computer and DMDX.