Response monitoring and expectancy in random serial RT tasks.

Two different sequential patterns have been reported in serial reaction-time (RT) tasks with random stimulus sequences, depending on the response-to-stimulus interval (RSI). When RSI is short a first-order repetition effect and a higher order benefit-only pattern are found, and when RSI is long a cost-benefit pattern is observed. In a series of three experiments, we found that the patterns are not unique for spatial dimensions, and that the benefit-only pattern does not appear for irrelevant stimulus features. The cost-benefit pattern, on the other hand, can shift to irrelevant locations, but not to irrelevant colour. Distributional analyses of the sequential effects demonstrate that the first-order repetition effect can be dissociated from the higher order effects. The results are interpreted as support for the role of response monitoring in the development of the benefit-only pattern at short RSI, while the first-order repetition effect is explained as repetition priming. With a long RSI, the cost-benefit pattern is confirmed as a low-level subjective expectancy process, which is primarily controlled by stimulus location. The data clearly strengthen the support for three different processes generating sequential effects in random serial RT tasks.