SENSORY AND PREPARATORY FACTORS IN RESPONSE LATENCY: The visual intensity function

Simple reaction times under irregular order of stimulus presentation are studied as a function of three luminous intensities viewed foveally and covering five log I units at the upper half of the brightness scale. Response latency varies inversely and rectilineariy with log I within this range. Respondents tend to converge in average latency but differ more in variability as stimulus strength is reduced, the more variable subjects even at high intensity suffering relatively greater loss in speed. Both positive and negative practice effects are observed, which seem partly dependent on stimulus intensity.