Simple reaction times to chromatic stimuli: Luminance and chromatic contrast

Abstract

This paper examines the effect of colour on reaction times for variations in both luminance and chromatic contrast. Results confirm the idea that reaction times are determined by a cone-opponent mechanism: Reaction times generated in response to S-cone isolating stimuli are the longest, whereas the shortest reaction times are generated by L—M-cone isolating stimuli. In addition, an asymmetry between ON and OFF opponent channels is observed for stimuli modulated on the blue—yellow axis. Reaction time (RT) is influenced by hue and chromatic contrast at isoluminant condition. In the isoluminant condition, RT decreases as luminance contrast increases. At luminance contrasts of approximately 20%, RT approaches an asymptotic value, thus becoming independent of colour for further luminance contrast increases. This asymptotic value is achieved for lower luminance contrasts as chromatic contrast increases.