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 middle letter l excerpted from two cursive trigrams (lll or lln) handwritten by one individual. The experimental factor was the distribution of the velocity 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 with the two-thirds power law, which describes how tangential velocity depends on curvature in writing movements. The task was to indicate the trigram from which the trace was excerpted--that is, to guess the letter that followed the specific instance of the l that had been displayed. In Experiment 1, the no answer option was available. Experiment 2 adopted a forced-choice response rule. Responses were never reinforced. When beta = 2/3, the rate of correct guesses was high (Experiment 1, P¿correct¿ = .69; Experiment 2, P¿correct¿ = .78). The probability of a correct answer decreased significantly for both smaller and larger values of beta, with wrong answers becoming predominant 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.