The long range effect of sleep on retention

A test is made of the hypothesis that a greater number of nonsense syllables will be retained after intervals of 24, 48 and 144 hours when learning is followed immediately by 8 hours sleep than when learning is followed by normal waking activities. The results for the 144-hour interval support the hypothesis at the p<.01 level of confidence but the differences at 48 and 24 hours are decreasing and insignificant. The possible roles of consolidation and interference are discussed and the need for further research into the critical period necessary for consolidation to occur is emphasized.