The interference effect of simultaneous vocalization on reaction time of hand and foot

Reaction times (RTs) of 14 normal subjects were examined in two tasks; the extension of the right middle finger, or of the right toe or the vocalization responding to the sound stimulation (single tasks), and the simultaneous responses of the two mentioned above (simultaneous tasks). RT of each part was longer on the simultaneous response than on the separate one. Slowing of the vocal response combined with the foot was larger than that with the hand and slowing of the foot with the vocalization was larger than that with the hand. The results were interpreted as indicating that the slowing of RT in the simultaneous responses should occur at the levels of the premotor associations, including the basal ganglia and cerebellum, but not at the level of the motor cortex.