A theory is presented to explain how accurate, single-joint movements are controlled. The theory applies to movements across different distances, with different inertial loads, toward targets of different widths over a wide range of experimentally manipulated velocities. The theory is based on three propositions. (1) Movements are planned according to “strategies” of which there are at least two: a speed-insensitive (SI) and a speed-sensitive (SS) one. (2) These strategies can be equated with sets of rules for performing diverse movement (...) tasks. The choice between SI and SS depends on whether movement speed and/or movement time (and hence appropriate muscle forces) must be constrained to meet task requirements. (3) The electromyogram can be interpreted as a low-pass filtered version of the controlling signal to the motoneuron pools. This controlling signal can be modelled as a rectangular excitation pulse in which modulation occurs in either pulse amplitude or pulse width. Movements to different distances and with loads are controlled by the SI strategy, which modulates pulse width. Movements in which speed must be explicitly regulated are controlled by the SS strategy, which modulates pulse amplitude. The distinction between the two movement strategies reconciles many apparent conflicts in the motor control literature. (shrink)

The simultaneous perception of multimodal sensory information is important for effective reactions to the external environment. In relation to the effect on time perception, voluntary movement and rhythmic stimuli have already been identified in previous studies to be associated with improved accuracy of temporal order judgments. Here, we examined whether the combination of voluntary movement and rhythmic stimuli improves the just noticeable difference in audio-tactile TOJ Tasks. Four different experimental conditions were studied, involving two types of (...) movements and two types of stimulus presentation. In the voluntary movement condition, after the auditory stimulus participants moved their right index finger voluntarily and naturally, while in the involuntary movement condition, their right index finger was moved by the tactile device. The stimuli were provided in a rhythmic or one-time only manner by hitting inside the first joint of the participants' right index finger using a tactile device. Furthermore, in the rhythmical tactile conditions, tactile stimuli were presented rhythmically to the right index finger 5 times consecutively. On the other hand, in the one-time tactile conditions, tactile stimuli was presented one-time only to the right index finger. Participants made an order judgment for the fifth tactile stimuli and the first and only auditory stimuli. In our TOJ tasks, auditory-tactile stimulus pairs were presented to participants with varying stimulus-onset asynchronies. For the two stimuli presented at a time that were shifted by the SOA, the participants were asked to judge which one was presented first, and they were given a two-choice answer. Using a non-parametric test, our results showed that voluntary movement and rhythmic tactile stimuli were both effective in improving the JNDs in TOJ Tasks. However, in the combination of voluntary movement and rhythmic tactile stimuli, we found that there was no significant difference in JNDs in our experiments. (shrink)

Duas das principais controvérsias que têm ocupado aqueles que se dedicam à teoria aris- totélica do movimento animal são a controvérsia acerca da forma da cognição através da qual um animal irracional apreende um objeto como um objeto de desejo e a controvérsia acerca da função desempenhada pela cognição na explicação aristotélica dos movimentos voluntários de locomoção animal. Neste artigo, eu apresento uma teoria acerca das formas como o desejo e a cognição se articulam na teoria aristotélica segundo a qual (...) um animal irracional apreende um objeto como um objeto de desejo através da percepção incidental deste objeto e, ao contrário do que a maioria parece acreditar, esta percepção não tem sempre a mesma função na produção destes movimentos. Se o que for dito aqui estiver correto, em alguns casos esta percepção é responsável tanto pela geração do desejo quan- to pela sua orientação, mas em outros ela é responsável apenas pela sua orientação. (shrink)

Benjamin Libet has argued that electrophysiological signs of cortical movement preparation are present before people report having made a conscious decision to move, and that these signs constitute evidence that voluntary movements are initiated unconsciously. This controversial conclusion depends critically on the assumption that the electrophysiological signs recorded by Libet, Gleason, Wright, and Pearl are associated only with preparation for movement. We tested that assumption by comparing the electrophysiological signs before a decision to move with signs present (...) before a decision not to move. There was no evidence of stronger electrophysiological signs before a decision to move than before a decision not to move, so these signs clearly are not specific to movement preparation. We conclude that Libet’s results do not provide evidence that voluntary movements are initiated unconsciously. (shrink)