Effector-dependent acquisition of novel typing sequences

In an earlier report we found that when pairs of letters were physically transposed on the keyboard and typists were required to type letters in their new location, the disruptions in typing were reduced when the transpositions involved mirror movements of homologous fingers of the two hands compared with transpositions involving the same hand. We hypothesized that acquisition may be facilitated when a new movement mirrors a previously learned movement. In order to test this hypothesis, in the present study we transposed various pairs of letters between the two hands. Experienced typists (n = 6) typed phrases in which a key was physically transposed with another key on the keyboard and subjects typed the letters in their new location (for 200 trials). The pairs of transpositions involved: (1) similar movements of homologous fingers; (2) different movements of homologous fingers; (3) similar movements of non-homologous fingers; and (4) different movements of non-homologous fingers. After the transposition of keys, there were non-uniform prolongations in the typing intervals of words containing transposed keys, with the largest delay occurring directly before the transposition. Practice had a differential effect on these intervals; some key press intervals achieved control levels, while others did not improve at all. The disruptions in typing were dependent on the specific keys transposed. Transpositions involving non-homologous digits of the two hands were less disruptive than transpositions involving homologous digits. The results do not support our earlier hypothesis that acquisition may be facilitated when a new movement mirrors a previously learned one. These results provide some possible insights into how distinct levels of movement organization develop in typing as a result of practice. Furthermore, the non-uniformity of the typing intervals in the words containing transposed keys supports the notion that typing is organized at multiple levels, including the individual key press and word level.