Laws of the unconditioned reflex in the rabbit nictitating membrane preparation

The unconditioned response (UR) of the rabbit’s nictitating membrane (NM) was examined as a function of the intensity and duration of electrotactile and airpuff unconditioned stimuli (USs). For both USs, increases in US intensity produced increases in UR likelihood and amplitude, and decreases in onset latency. Increases in US duration had similar but smaller effects on the UR. The peak latency of the UR was also examined, but it proved to be highly variable. The data were analyzed by using progressively larger NM movements to define a UR. The lower criteria of 0.125, 0.250, and 0.500 mm produced virtually identical results. The more stringent criteria of 0.750, 1, and 2 mm produced decreases in the observed UR likelihood, increases in apparent UR amplitude, and increases in apparent peak latency.