ABSTRACT
Welford (1952) carried out an experiment that showed that when two signals are presented in rapid succession and the subject must make a speeded response to both, reaction time to the second stimulus depends on the stimulus onset asynchrony (SOA) between the presentation of the first and second stimulus. When the second stimulus is presented after only a very short SOA, reaction time to the second stimulus is slower than when there is a long SOA between stimuli. Welford called this delay in response to a second stimulus in the short SOA condition the “psychological refractory period” (PRP). Welford was able to show that for every millisecond decrease in SOA there was a corresponding increase in reaction time to the second stimulus.
