Effects of changing compatibility relationships on reaction time to the first stimulus in a double-stimulation task

This study investigated the effects of manipulating the response requirement to the second stimulus (S2) on reaction time (RT) to the first stimulus (S1) in a double-stimulation choice RT task. Forty subjects responded to the 100 msec presentation of a left or right light by pressing the key on the same or opposite side as the light. Treatment conditions included a single-stimulation control (no S2 presented), and two double-stimulation conditions each requiring two responses (R1 and R2) in close succession, in one of these latter conditions, the rule governing R2 was the same as that governing R1 while, in the other, the rule governing R2 changed. Results showed the typical double-stimulation effect; i.e., increased latency of R1 when it was followed by S2 - R2. More importantly, R1 latency was increased further when the rules governing R1 and R2 were different. Results are discussed in terms of divided preparation capacity as well as other theories of the psychological refractory period.