Results of the (a) primary HTR task, (b) secondary vibrotactile task, and (c) response times in the secondary vibrotactile task. Proportion correct (for the primary and secondary vibrotactile task) and accumulated response times in seconds (for the secondary vibrotactile task) are plotted as a function of the masker condition (silence, pseudo-speech, speech) and the number of tasks (single-task, dual-task), averaged per participant. The boxes represent the interquartile ranges, while the median is indicated with a horizontal line and the mean with a red circle.