S-R compatibility effects without response uncertainty

Five experiments investigated whether cognitively based spatial S-R correspondence effects or ''compatibility'' effects can occur in simple reaction time (SRT) tasks and if so, which factors might be responsible for their occurrence and size. In Experiment 1, responses were cued before each trial, but made only after presentation of a Go signal. There were considerably faster responses with spatial correspondence of Go signal and response, demonstrating that response certainty does not prevent a compatibility effect. Experiment 2, a SRT task with ''extra'' trials requiring responses with the same or the opposite hand, indicated a major determinant of this effect to be the keeping of two task-relevant responses in a state of readiness. Experiment 3 provided preliminary evidence for ''inertia'' effects-that is, for stronger correspondence effects with frequent than with infrequent alternations between left-hand and right-hand blocks. Experiment 4 showed that correspondence effects can be obtained by using a within-hand response repertoire. Experiment 5, a replication of Experiment 3 with within-hand responses, found further evidence for inertia effects. For all experiments, reaction time distribution analyses were carried out to gain insight into the temporal dynamics of correspondence effects. Altogether the results strongly suggest that most if not all correspondence effects had a cognitive rather than an anatomical origin. This raises some doubts about conclusions from prior attempts to measure interhemispheric transmission costs by means of SRT tasks.