Vibrotactual choice reaction time,tactile receptor systems and ideomotor compatibility

In most of the literature on human performance the results of an experiment by Leonard (1959) are quoted as the most outstanding example of perfect S-R-compatibility. In that experiment the fingertips were stimulated by a 50 Hz vibration; the vibrating armature had to be depressed and the reaction times of the right index finger were recorded. The reaction time was found not to increase with an increasing number of tactual choices. In experiment 1 of the present study, also applying 50 Hz vibrations, the reaction times of other fingers were also reported. In addition the response stimulus interval (RSI) was varied. Leonard's results were not replicated: reaction time increased with the number of tactual choices at all levels of RSI. In experiment 2 the frequency and amplitude of vibration were systematically varied and it turned out that these variables could account for the differences between the results found. An increase in reaction time with the number of tactual choices was found with weak vibrations, but not with strong vibrations. The differences in reaction time patterns appeared to be caused by differences in tactile receptor systems (i.e. the non-Pacini versus the Pacinian system). It was concluded that the concept of S-R-compatibility did not cover the pattern of results but that the concept of ideomotor compatibility did.