Is judgment of random time intervals biased and capacity-limited?

Recently, random generation of time intervals has been proposed as a proced ure to impair executive processing in a dual-task paradigm without substant ial interference with phonological and visuo-spatial working memory resourc es. A fundamental assumption of this procedure is that humans are able to d istinguish time sequences on their degree of randomness. The present study tests this assumption. To this end, nonbiased, repetition-biased, alternati on-biased sequences and repetitive rhythms were judged under conditions of higher or lower executive load. In Exp. 1, load depended on the presentatio n speed, while in Exp. 2, a dual-task condition was used with either a conc urrent number-copying task or an arithmetic task. It was found that the par ticipants could distinguish repetitive rhythms from more or less random seq uences, and that both accuracy of this judgment and latency were affected b y the concurrent load. The findings are taken as a first indication that ra ndom time judgment is capacity-limited.