Sequential Redundancy and Speed in a Serial Two-Choice Responding Task

The task used is a self-paced 2-choice serial responding task, involving two neon lamps as signals and two response keys in simple spatial correspondence with the signals. In Experiment 1, three conditions with respectively 1/4, 1/2 and 3/4 alternations between successive signals were compared. It appeared that subjects go faster with 1/4 than with 3/4 alternations. From the point of view of information theory, both conditions present the same amount of information per signal. The asymmetry in the effects of both forms of sequential redundancy could be attributed either to some bias in the expectations of the subjects or to some inertia phenomenon favouring responses to repeated signals. It was reasoned that if the last explanation was true, the asymmetry would be reduced if a time-lag was introduced between end of response and appearance of next signal. This was done for one group of subjects in Experiment 2. These subjects worked on the same three conditions, with a time-lag of 0.5 sec. The asymmetry was significantly reduced when compared with another group of subjects who worked with the same 0.05 sec. time-lag as in Experiment 1. Analysis of separate RTs confirmed the main conclusion that choice processes involve a transitory residual effect favouring repetitions.