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A labial perturbation of the French rounded vowel [u] was used to examine the respective weights of the articulatory and acoustic levels in the control of vowel production. A 20-mm-diam lip tube was inserted between the lips of the speakers. Acoustic and x-ray articulatory data were obtained for isolated vowel productions by 11 native French speakers in normal and lip-tube conditions. Compensation abilities were evaluated through accuracy of the F1-F2 pattern. Possible compensations were examined from nomograms using the new model of Fant [ISCLP 92 Proceedings (University of Alberta, Edmonton, 1992)]. Acoustic interpretations of the articulatory changes were made by generating area functions from midsagittal views, used together with a harmonic acoustic model. For the first perturbed trial, immediately after the insertion of the tube, no speaker was able to produce a complete compensation, but clear differences between speakers were observed: Seven of them moved the tongue and hence limited the deterioration of the F1-F2 pattern, whereas the remaining four did not show any pertinent articulatory change. These data support the idea of speaker-specific internal representations of the articulatory-to-acoustic relationships. The results for the following 19 perturbed trials indicate that speakers used the acoustic signal in order to elaborate an optimal compensation strategy. One speaker achieved complete compensation by changing his constriction location from a velo-palatal to a velo-pharyngeal region of the vocal tract. Six others moved their tongues in the right direction, achieving partial acoustic compensation, while the remaining four did not compensate. The control of speech production thus seems to be directed toward achieving an auditory goal, but completely achieving the goal may be impossible because of speaker-dependent articulatory constraints. It is suggested that these constraints are due more to speaker-specific internal representation of articulatory-to-acoustic relationships rather than to anatomical or neurophysiological limitations. Speech control could thus be ensured partly with the use of this internal representation, and partly--particularly under perturbed conditions--by monitoring the acoustic signal. ¸ 1995 Acoustical Society of America.

The execution of a graphemic sequence is constrained by spatial demands that result in fluctuations of letter shape and movement time. When producing two letters (ll, le, or ln) the movement time and the letter shape of the first letter depend on the execution constraints of the second one. The motor system thus anticipates the production of the forthcoming graphemic sequence during the production of the first letter. An experiment is reported the aim of which was to examine whether the visual system could exploit this anticipatory information to predict the identity of the letter following the l. Different ls belonging to ll, le, and ln were presented on a screen. Subjects had to predict to which couple of letters (ll, le, or ln) the presented l belonged to, by using information on the shape of the l and/or the movement that produced it. Results showed that the percentages of correct responses were higher in the conditions where the stimulus provided kinematic information than in the condition in which only spatial information was available. The ability to predict the forthcoming letter seems to be mediated by implicit knowledge on motor anticipation rules.

In human newborns, spontaneous visual preference for biological motion is reported to occur at birth, but the factors underpinning this preference are still in debate. Using a standard visual preferential looking paradigm, 4 experiments were carried out in 3-day-old human newborns to assess the influence of translational displacement on perception of human locomotion. Experiment 1 shows that human newborns prefer a point-light walker display representing human locomotion as if on a treadmill over random motion. However, no preference for biological movement is observed in Experiment 2 when both biological and random motion displays are presented with translational displacement. Experiments 3 and 4 show that newborns exhibit preference for translated biological motion (Experiment 3) and random motion (Experiment 4) displays over the same configurations moving without translation. These findings reveal that human newborns have a preference for the translational component of movement independently of the presence of biological kinematics. The outcome suggests that translation constitutes the first step in development of visual preference for biological motion.

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 I excerpted from two cursive trigrams (lU or Un) handwritten by one individual. The experimental factor was the distribution of the velocity along the trace, which was controlled by a single parameter, {3. Only for one value of this parameter ({3 =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 I 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{3 =2/3,the rate of correct guesses was high (Experiment 1,PI correctJ = .69; Experiment 2, P(correctj = .78). The probability of a correct answer decreased significantly for both smaller and larger values of {3, 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.

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A large body of psychophysical evidence suggests that perception of human movement is constrained by the observer's motor competence. PET measurements of regional cerebral blood flow were performed in eight healthy subjects who were requested, in a forced-choice paradigm, to anticipate the outcome of a single moving dot trajectory depicting the beginning of either mechanical, pointing, or writing movements. Selective activation of the left premotor cortex and of the right intraparietal sulcus was associated with visual anticipation of pointing movements while the left frontal operculum and superior parietal lobule were found to be activated during anticipation of writing movements. These results are discussed in the perspective that the motor system is part of a simulation network, which is used to interpret perceived actions.