All stimuli were presented on a 19-inch cathode-ray tube display at a resolution of 1280 × 1024 pixels, at a viewing distance of 52 cm. Stimulus presentation and response collection were controlled by a personal computer running of the Windows XP platform, and using Psychophysics Toolbox extensions (Brainard, 1997; Pelli, 1997) on Matlab (Mathworks Inc.).