An electromyographic examination of response competition

Abstract

Subjects were required to discriminate the letters S and H in a choice reaction time task. They responded with a thumbpress of one hand to one of the letters and with the thumb of the other hand to the other letter. In the incompatible noise condition, the target letter was flanked by the opposite response letter, and in the compatible noise condition, the flanking noise letters were identical to the target. In addition to overt reaction time, associated electromyographic activity was recorded in both arms on each trial. In keeping with previous findings, incompatible noise significantly and appreciably increased reaction time for the overt response. More importantly, in the incompatible condition, the occurrence of a correct thumb response was frequently accompanied by an EMG in the arm appropriate to the noise letters. This result was interpreted as showing that the noise letters were processed to the point of incipient response activation simultaneously with the target letter. The results were predicted by the continuous flow model of C. W. Eriksen and Schultz (1979) and the variable criterion theory of Grice, Nullmeyer, and Spiker (1982).