Simple reaction time as a function of number and similarity of sequenced elements in rapid force production

Two experiments were conducted to examine the effects of number and similarity of sequenced elements on simple reaction time (RT). In Exp. 1, subjects were required to initiate and execute sequences of one to three homogeneous or heterogeneous force elements by squeezing the handle as quickly and accurately as possible. Simple RTs and premotor times increased from one to two elements, with no further increases thereafter, regardless of whether the sequences were comprised of homogeneous or heterogeneous elements. The number of elements did not affect the production of interelement interval. In Exps. 1 and 2, however, simple RTs and premotor times to initiate the sequences were longer for the heterogeneous conditions than for the homogeneous conditions. These findings did not support the assumption of the 1978 subprogram retrieval model of Sternberg, Monsell, Knoll, and Wright that only the first element in the sequence is retrieved and programmed during a simple-RT interval. These findings also suggest that similarity of sequenced elements is one factor which affects the complexity of the motor-programming process.