Central tendency and serial dependence in vestibular path integration.

Path integration, the process of updating one's position using successive self-motion signals, has previously been studied with visual distance reproduction tasks in which optic flow patterns provide information about traveled distance. These studies have reported that reproduced distances show two types of systematic biases: central tendency and serial dependence. In the present study, we investigated whether these biases are also present in vestibular path integration.

Early-Stage Alzheimer's Disease Affects Fast But Not Slow Adaptive Processes in Motor Learning.

Alzheimer's disease (AD) is characterized by an initial decline in declarative memory, while nondeclarative memory processing remains relatively intact. Error-based motor adaptation is traditionally seen as a form of nondeclarative memory, but recent findings suggest that it involves both fast, declarative, and slow, nondeclarative adaptive processes. If the declarative memory system shares resources with the fast process in motor adaptation, it can be hypothesized that the fast, but not the slow, process is disturbed in AD patients.

Natural statistics of head roll: implications for Bayesian inference in spatial orientation.

We previously proposed a Bayesian model of multisensory integration in spatial orientation (Clemens IAH, de Vrijer M, Selen LPJ, van Gisbergen JAM, Medendorp WP. J Neurosci 31: 5365-5377, 2011). Using a Gaussian prior, centered on an upright head orientation, this model could explain various perceptual observations in roll-tilted participants, such as the subjective visual vertical, the subjective body tilt (Clemens IAH, de Vrijer M, Selen LPJ, van Gisbergen JAM, Medendorp WP.

Assessing corticospinal excitability and reaching hand choice during whole body motion.

Behavioral studies have shown that humans account for inertial acceleration in their decisions of hand choice when reaching during body motion. Physiologically, it is unclear at what stage of movement preparation information about body motion is integrated with the process of hand selection. Here, we addressed this question by applying transcranial magnetic stimulation over left motor cortex (M1) of human participants who performed a preferential reach task while they were sinusoidally translated on a linear motion platform.

Even well-practiced movements benefit from repetition.

Professional golfers spend years practicing, but will still perform one or two practice swings without a ball before executing the actual swing. Why do they do this? In this study, we tested the hypothesis that repeating a well-practiced movement leads to a reduction of movement variability. To operationalize this hypothesis, participants were tested in a center-out reaching task with four different targets, on four different days.

Cortical beta-band power modulates with uncertainty in effector selection during motor planning.

Although beta-band activity during motor planning is known to be modulated by uncertainty about where to act, less is known about its modulations to uncertainty about how to act. To investigate this issue, we recorded oscillatory brain activity with EEG while human participants ( = 17) performed a hand choice reaching task. The reaching hand was either predetermined or of participants' choice, and the target was close to one of the two hands or at about equal distance from both.

Movement preparation time determines movement variability.

Faster movements are typically more variable-a speed-accuracy trade-off known as Fitts' law. Are movements that are initiated faster also more variable? Neurophysiological work has associated larger neural variability during motor preparation with longer reaction time (RT) and larger movement variability, implying that movement variability decreases with increasing RT. Here, we recorded over 30,000 reaching movements in 11 human participants who moved to visually cued targets.

Correction: Reward abundance interferes with error-based learning in a visuomotor adaptation task.

[This corrects the article DOI: 10.1371/journal.pone.

Vestibular modulation of visuomotor feedback gains in reaching.

Humans quickly and sophisticatedly correct their movements in response to changes in the world, such as when reaching to a target that abruptly changes its location. The vigor of these movement corrections is time-dependent, increasing if the time left to make the correction decreases, which can be explained by optimal feedback control (OFC) theory as an increase of optimal feedback gains. It is unknown whether corrections for changes in the world are as sophisticated under full-body motion.

State Estimation for Early Feedback Responses in Reaching: Intramodal or Multimodal?

Humans are highly skilled in controlling their reaching movements, making fast and task-dependent movement corrections to unforeseen perturbations. To guide these corrections, the neural control system requires a continuous, instantaneous estimate of the current state of the arm and body in the world. According to Optimal Feedback Control theory, this estimate is multimodal and constructed based on the integration of forward motor predictions and sensory feedback, such as proprioceptive, visual and vestibular information, modulated by context, and shaped by past experience.

Cerebellar tDCS dissociates the timing of perceptual decisions from perceptual change in speech.

Neuroimaging studies suggest that the cerebellum might play a role in both speech perception and speech perceptual learning. However, it remains unclear what this role is: does the cerebellum help shape the perceptual decision, or does it contribute to the timing of perceptual decisions? To test this, we used transcranial direct current stimulation (tDCS) in combination with a speech perception task. Participants experienced a series of speech perceptual tests designed to measure and then manipulate (via training) their perception of a phonetic contrast.

Competition between movement plans increases motor variability: evidence of a shared resource for movement planning.

Do movement plans, like representations in working memory, share a limited pool of resources? If so, the precision with which each individual movement plan is specified should decrease as the total number of movement plans increases. To explore this, human participants made speeded reaching movements toward visual targets. We examined if preparing one movement resulted in less variability than preparing two movements.

Exposing sequence learning in a double-step task.

Is it possible to learn to perform a motor sequence without awareness of the sequence? In two experiments, we presented participants with the most elementary sequence: an alternation between two options. We used a double-step pointing task in which the final position of the target alternated between two quite similar values. The task forced participants to start moving before the final target was visible, allowing us to determine participants' expectations about the final target position without explicitly asking them.

Reacting With or Without Detecting.

We begin our response by clarifying the concept of detection, and explaining why this is needed for initiating, but not for adjusting a movement. We present a simulation to illustrate this difference. Several commentators referred to studies with results that might seem in conflict with our proposal that movement adjustments have short latencies because there is no need to detect anything.

Evidence for Optimal Integration of Visual Feature Representations across Saccades.

Unlabelled: We explore the visual world through saccadic eye movements, but saccades also present a challenge to visual processing by shifting externally stable objects from one retinal location to another. The brain could solve this problem in two ways: by overwriting preceding input and starting afresh with each fixation or by maintaining a representation of presaccadic visual features in working memory and updating it with new information from the remapped location. Crucially, when multiple objects are present in a scene the planning of eye movements profoundly affects the precision of their working memory representations, transferring limited memory resources from fixation toward the saccade target.

Movement Adjustments Have Short Latencies Because There is No Need to Detect Anything.

We can adjust an ongoing movement to a change in the target's position with a latency of about 100 ms, about half of the time that is needed to start a new movement in response to the same change in target position (reaction time). In this opinion paper, we discuss factors that could explain the difference in latency between initiating and adjusting a movement in response to target displacements. We consider the latency to be the sum of the durations of various stages in information processing.

Online manual movement adjustments in response to target position changes and apparent target motion.

This study set out to determine whether the fastest online hand movement corrections are only responses to changing judgments of the targets' position or whether they are also influenced by the apparent target motion. Introducing a gap between when a target disappears and when it reappears at a new position in a double-step paradigm disrupts the apparent motion, so we examined the influence of such a gap on the intensity of the response. We found that responses to target perturbations with disrupted apparent motion were less vigorous.

Comparing online adjustments to distance and direction in fast pointing movements.

It has been suggested that movements are planned in terms of direction and distance. If so, online adjustments to changes in the direction and distance of the movements may also differ. The authors therefore investigated whether fast online movement adjustments are the same for perturbations of the direction and of the distance.

Analysis of methods to determine the latency of online movement adjustments.

When studying online movement adjustments, one of the interesting parameters is their latency. We set out to compare three different methods of determining the latency: the threshold, confidence interval, and extrapolation methods. We simulated sets of movements with different movement times and amplitudes of movement adjustments, all with the same known latency.

Fast and fine-tuned corrections when the target of a hand movement is displaced.

To study the strategy in responding to target displacements during fast goal-directed arm movements, we examined how quickly corrections are initiated and how vigorously they are executed. We perturbed the target position at various moments before and after movement initiation. Corrections to perturbations before the movement started were initiated with the same latency as corrections to perturbations during the movement.

Visuomotor transformation for interception: catching while fixating.

Catching a ball involves a dynamic transformation of visual information about ball motion into motor commands for moving the hand to the right place at the right time. We previously formulated a neural model for this transformation to account for the consistent leftward movement biases observed in our catching experiments. According to the model, these biases arise within the representation of target motion as well as within the transformation from a gaze-centered to a body-centered movement command.

Adaptations of lateral hand movements to early and late visual occlusion in catching.

Recent studies suggested that the control of hand movements in catching involves continuous vision-based adjustments. More insight into these adjustments may be gained by examining the effects of occluding different parts of the ball trajectory. Here, we examined the effects of such occlusion on lateral hand movements when catching balls approaching from different directions, with the occlusion conditions presented in blocks or in randomized order.