Cross-modal psychological refractory period in vision, audition, and haptics.

People's parallel-processing ability is limited, as demonstrated by the psychological refractory period (PRP) effect: The reaction time to the second stimulus (RT2) increases as the stimulus onset asynchrony (SOA) between two stimuli decreases. Most theoretical models of PRP are independent of modalities. Previous research on PRP mainly focused on vision and audition as input modalities; tactile stimuli have not been fully explored. Research using other paradigms and involving tactile stimuli, however, found that dual-task performance depended on input modalities. This study explored PRP with all the combinations of input modalities. Thirty participants judged the magnitude (small or large) of two stimuli presented in different modalities with an SOA of 75-1,200 ms. PRP effect was observed, i.e., RT2 increased with a decreasing SOA, in all the modalities. Only in the auditory-tactile condition did the accuracy of Task 2 decrease with a decreasing SOA. In the auditory-tactile and tactile-visual conditions, RT to the first stimulus also increased with a decreasing SOA. Current models could only explain part of the results, and modality characteristics help to explain the overall data pattern better. Limitations and directions for future studies regarding reaction time, task difficulty, and response modalities are discussed.