Probing the response selection bottleneck with a cardiac measure: individual differences in strategy for a psychological refractory period task

We examined the coordination of processing streams when two reaction stimuli are presented with minimal temporal separation (the psychological refractory period, PRP, paradigm). We tested the hypothesis that individuals that grouped responses to the two stimuli would schedule response preparation later than those not-grouping their responses would. Performance measures were combined with a cardiac measure interpreted as an index of response inhibition. Forty-two college-aged participants performed an auditory choice task followed in 50, 100 or 400 ms by a visual choice reaction time (RT) task. Performance results replicated prior work. The timing of cardiac inter-beat intervals (IBIs) showed that participants grouping their reactions did appear to delay response preparation; while Non-Groupers promptly initiated response selection for the initial task. These results generally supported the importance of preparation for understanding the coordination of processing streams.