Does motor programming necessitate response execution?

The complexity of a movement is known to affect the time it takes to initiate the movement. This effect is thought to reflect changes in the duration of processes that operate on a motor program. This question addressed here is whether programming a movement compels the start of its overt execution. If it does, then the programming processes may be said to occur after the "point of no return." We report results from an empirical procedure and a theoretical analysis designed to study processes before and after this point separately. According to our results, changes in the complexity of a movement affect only the prior set of processes. From this we argue that motor programming does not necessitate response execution and that the point of no return occurs very late in the information-processing system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The point of no return in choice reaction time: Controlled and ballistic stages of response preparation.

Used a countermanding procedure and race model to assess separately the effects of experimental factors before and after the "point of no return" in response preparation (i.e., where the decision to move becomes irrevocable) in 3 experiments with 22 undergraduates. Results reveal details about processes that so closely precede the initiation of movement that they cannot be inhibited. These processes appear to be affected by the repetition of stimulus–response pairs but not by the physical or semantic properties of the stimuli. Findings support a model of response preparation in which (a) response inhibition depends on the outcome of a race between independent excitatory and inhibitory processes and (b) reaction time (RT) is the sum of the durations of at least 2 stages, separated by the point of no return. (54 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Distributional analysis and De Jong, Liang, and Lauber's (1994) dual-process model of the Simon effect.

R. De Jong et al (1994) proposed a dual-process model to account for the Simon effect and its reversal. Their proposal included a distributional analysis whose results, they claimed, support the time-course assumptions they make for the 2 processes of the model. It is shown that the 2 functional components of the dual-process model, the unconditional and conditional automaticity, are equivalent to earlier accounts of the Simon effect and its reversal, namely automatic response activation of the dimensional overlap model (S. Kornblum et al, 1990) and logical recoding (A. Hedge & N. W. A. Marsh, 1975), respectively. It is also shown that the distributional analysis is a simple computational procedure that reflects fundamental statistical properties of the underlying RT distributions and their interrelationships and that the time-course assumptions by De Jong et al precluded at least half of these interrelationships. Indeed, experimental results from tasks in which the Simon effect is obtained often violate these assumptions, as is demonstrated in this article. Finally, it is also shown that the data by De Jong et al are consistent with the hypothesis that the Simon effect and its reversal can be accounted for by a common mechanism with 2 independent functional components. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cooperation,scale-invariance and complex innovation systems: a generalization

Scientometrics - The focus of this paper is the question “Can scale-invariant properties of collaborative research activities of a complex innovation system be quantified, modeled and used to...     

Jacobian Matrix for Solving Water Distribution System Equations with the Darcy-Weisbach Head-Loss Model

The widely used Todini and Pilati method for solving the equations that model water distribution systems was originally developed for pipes in which the head loss is modeled by the Hazen-Williams formula. The friction factors in this formula are independent of flow. Rossman’s popular program EPANET implements elements of the Todini and Pilati algorithm, but when the Darcy-Weisbach head-loss formula is used, it does not take into account the dependence of the friction factors on the Reynolds number, and therefore flow, in computing the Jacobian. We present the correct Jacobian matrix formulas, which must be used in order to fully account for the friction factor’s dependence on flow when the Todini and Pilati method is applied with the Darcy-Weisbach head-loss formula. With the correct Jacobian matrix the Todini and Pilati implementation of Newton’s method has its normally quadratic convergence restored. The new formulas are demonstrated with an illustrative example.     

Neuronal correlates of sensorimotor association in stimulus–response compatibility.

Neuronal mechanisms underlying stimulus–response (S-R) associations in S-R compatibility tasks were identified in 2 experiments with monkeys. Visual stimuli were presented on the left and right calling for left–right movements under congruent and incongruent S-R mapping instructions. High- and low-pitched tones calling for left–right movements were presented to the left and right ear, and the stimulus side was irrelevant. Single neurons sensitive to the S-R mapping rule were found in the primary motor cortex. The large overlap between the neuronal populations sensitive to the stimulus side, the S-R mapping rule, and the response side, respectively, is consistent with the idea that sensory-to-motor transformation is a continuous rather than a discrete process. Results partly support the hypothesis that the increase in reaction time with incongruent mapping is caused by the automatic activation of the congruent, but erroneous, response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eye-hand coordination: Oculomotor control in rapid aimed limb movements.

Three experiments are reported in which Ss produced rapid wrist rotations to a target while the position of their eyes was being monitored. In Experiment 1, Ss spontaneously executed a saccadic eye movement to the target around the same time as the wrist began to move. Experiment 2 revealed that wrist-rotation accuracy suffered if Ss were not allowed to move their eyes to the target, even when visual feedback about the moving wrist was unavailable. In Experiment 3, wrist rotations were equally accurate when Ss produced either a saccadic or a smooth-pursuit eye movement to the target. However, differences were observed in the initial-impulse and error-correction phases of the wrist rotations, depending on the type of eye movement involved. The results suggest that aimed limb movements use information from the oculomotor system about both the static position of the eyes and the dynamic characteristics of eye movements. Furthermore, the information that governs the initial impulse is different from that which guides final error corrections. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Design of a Piezoelectric Heart Assist Device

A piezoelectric heart assist device was designed, and preliminary tests were performed in vitro and in vivo. The device has the advantages of simple construction, low power consumption (approximately one watt), electrical rather than pneumatic drive, and noiseless operation. The device consists of piezoelectric bender elements forming two cantilevers. A unique feature of the device is that two tungsten alloy masses, 0.44 kg each, were added to the free ends of the cantilevers to reduce the resonant frequency to 2.5 Hz. The driving voltage was a 320 V peak-to-peak square wave synchronized with a paced heartbeat.