Displaying 1 of the 4 colored circles on the screen generated stimuli for movement. Only 1 colored circle appeared at a time; the other circles were transparent. However, each colored circle always appeared in the same position and thus maintained its relative location on the screen and to the corresponding key. Following the appearance of 1 colored circle and prior to the display of the next colored circle, a large black asterisk, centered on the screen, served as a fixation point. Responses were made by pressing 1 of the 4 keys corresponding (in color and location) to the appropriately colored circle. A custom-designed computer software program (L Boyd, 2000, E-Prime software platform, version Beta 5.0)* controlled the appearance of the colored circles and recorded the participants' responses. Time data (response time [RT]) were stored after every key press for future analysis.