The delayed stimulus suffix effect following arhythmic stimulus presentation

In auditory memory span experiments an extra word presented at the end of the list impairs performance on the last few items even though it is completely redundant; delaying this stimulus suffix past the time when an additional memory item would have occurred--so that the rate of presentation is retarded for the suffix--reduces the magnitude of the performance impairment. One account of this pattern of results is that during presentation of the items the subject adjusts periodic bursts of attention to the regular cadence of new information. Since an immediate suffix is in time with this cadence and a delayed suffix not, the larger effect of the former is explained without appeal to any process dependent on real time. In the present study the stimulus items were presented in an arhythmic manner with interstimulus intervals ranging from 100 to 900 ms on a random basis. Under these conditions the same effect of delaying the suffix was observed as is typical of rhythmic stimulus presentation; therefore, the rhythm hypothesis for the effect is not supported.