Perceptual anticipation in handwriting: The role of implicit motor competence

In two experiments, perceptual anticipation-that is, the observer's ability to predict the course of dynamic visual events-in the case of handwriting traces was investigated. Observers were shown the dynamic display of the mi ddle letter iota excerpted from two cursive trigrams (lll or lln) handwritt en by one individual. The experimental factor was the distribution of the v elocity along the trace, which was controlled by a single parameter, beta. Only for one value of this parameter (beta = 2/3) did the display comply wi th the two-thirds power law, which describes how tangential velocity depend s on curvature in writing movements. The task was to indicate the trigram f rom which the trace was excerpted-that is, to guess the letter that followe d the specific instance of the l that had been displayed. In Experiment i, the no answer option was available. Experiment 2 adopted a forced-choice re sponse rule. Responses were never reinforced. When beta = 2/3, the rate of correct guesses was high (Experiment 1, P(correct) = .69; Experiment 2, P(c orrect) = .78). The probability of a correct answer decreased significantly for both smaller and larger values of beta, with wrong answers becoming pr edominant at the extremes of the range of variation of this parameter. The results are consistent with the hypothesis that perceptual anticipation of human movements involves comparing the perceptual stimulus with an internal dynamic representation of the ongoing event.