On the Locus of Speed-Accuracy Trade-Off in Reaction Time: Inferences From the Lateralized Readiness Potential.

Lateralized readiness potentials (LRPs) were used to determine the stage(s) of reaction time (RT) responsible for speed-accuracy trade-offs (SATs). Speeded decisions based on several types of information were examined in 3 experiments, involving, respectively, a line discrimination task, lexical decisions, and an Erikson flanker task. Three levels of SAT were obtained in each experiment by adjusting response deadlines with an adaptive tracking algorithm. Speed stress affected the duration of RT stages both before and after the start of the LRP in all experiments. The latter effect cannot be explained by guessing strategies, by variations in response force, or as an indirect consequence of the pre-LRP effect. Contrary to most models, it suggests that SAT can occur at a late postdecisional stage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brief bimanual force pulses: Correlations between the hands in force and time.

Three experiments assessed coupling phenomena in the coordination of bimanual force pulses. Experiment 1 required symmetric force pulses (equal target forces and rise times for both hands) using the index finger of each hand. As the authors expected, on the basis of bimanual pointing movement results, this experiment revealed positive correlations between both the force rise times and the force amplitudes of the two hands. Experiments 2 and 3 included asymmetric conditions with different target force amplitudes (Experiment 2) or target rise times (Experiment 3). In Experiment 2 force amplitudes but not rise times were fully decoupled in the asymmetric condition. In the asymmetric condition of Experiment 3, however, neither rise times nor force amplitudes were fully decoupled. The results suggest a hierarchical control structure with temporal control dominating nontemporal control of bimanual force coordination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amplitude and duration scaling of brief isometric force pulses.

The predictions of 2 rival models for the production of brief isometric force pulses were tested in 3 experiments. The prototype-function model assumes that an observable force pulse emerges from an underlying prototypical function by scaling its duration and amplitude. The parallel-force unit model (PFUM) assumes that force pulses emerge from the concerted activity of a large number of force units with invariant form. Exp 1 showed that the shape of single-trial force-time functions depends mainly on their rise times but not on their amplitudes. Exp 2 tested the same predictions for mean force-time functions at 3 levels of rise time and 3 levels of peak force. Exp 3 examined shape constancy for less forceful pulses. In sum, the results indicate that the shape of force pulses is approximately preserved if they vary in amplitude but not in duration. They become more symmetrical as rise time increases. This finding does not support a prototype-function model and supports the predictions of PFUM. Some additional findings on force variability are discussed and compared with the predictions of PFUM. The data suggest some modifications of PFUM. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of stimulus intensity on the lateralized readiness potential.

Information-processing models differ about whether stimulus intensity affects the speed of motor processes involved in response activation and execution. Previous studies of intensity are reviewed, but they are not decisive on this point because they have used indirect approaches requiring strong assumptions. Two experiments examined the effects of stimulus intensity on the lateralized readiness potential (LRP), a measure of hand-specific response activation. In Experiment 1, visual stimulus intensity influenced the time from stimulus onset to LRP onset but not the time from LRP onset to the keypress response. In Experiment 2, auditory stimulus intensity did not influence either of these time intervals, although it did influence the time from stimulus onset to the N100 and P300 components of the evoked potential. The results indicate that stimulus intensity does not influence the duration of motor processes in choice reaction time tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of stimulus duration and intensity on simple reaction time and response force.

Previous research indicates that response force increases with stimulus intensity in simple reaction time (SRT) tasks. This result contradicts the common view that the perceptual system activates the motor system via a punctate go signal of fixed size. An elaborated view assumes that the size of the go signal depends on stimulus intensity so that more intense stimuli yield more forceful responses. In order to examine the latter hypothesis, the present experiments manipulated stimulus duration as well as intensity. Response force increased with duration even beyond a critical value of about 60 ms at which stimulus duration no longer affected SRT. In addition, increasing the duration of a stimulus also increased the duration of force output. These findings argue against models with punctate transmission of activation to the motor system. Certain continuous models and variable output models with prolonged go signals provide acceptable accounts of these effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)