Publications by authors named "Romeo Chua"

Implicit sensorimotor adaptation keeps our movements well calibrated amid changes in the body and environment. We have recently postulated that implicit adaptation is driven by a perceptual error: the difference between the desired and perceived movement outcome. According to this perceptual realignment model, implicit adaptation ceases when the perceived movement outcome-a multimodal percept determined by a prior belief conveying the intended action, the motor command, and feedback from proprioception and vision-is aligned with the desired movement outcome.

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When paired participants are each assigned a complementary half of the Simon task, a joint Simon effect (JSE) has been observed. Co-representation, a cognitive representation of not only one's own task but also that of the co-actor, has been one of several proposed mechanisms in the JSE. Using the response-discrimination hypothesis as a framework, we tested whether it was sufficient to highlight alternative task keys in a two-person setting in which a non-complementary task was completed to elicit a Simon effect (SE).

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Tendon vibration is used extensively to assess the role of peripheral mechanoreceptors in motor control, specifically, the muscle spindles. Periodic tendon vibration is known to activate muscle spindles and induce a kinesthetic illusion that the vibrated muscle is longer than it actually is. Noisy tendon vibration has been used to assess the frequency characteristics of proprioceptive reflex pathways during standing; however, it is unknown if it induces the same kinesthetic illusions as periodic vibration.

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Height-induced postural threat affects emotional state and standing balance behaviour during static, voluntary, and dynamic tasks. Facing a threat to balance also affects sensory and cortical processes during balance tasks. As sensory and cognitive functions are crucial in forming perceptions of movement, balance-related changes during threatening conditions might be associated with changes in conscious perceptions.

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It has been proposed that sensory force/pressure cues are integrated within a positive feedback mechanism, which accounts for the slow dynamics of human standing behavior and helps align the body with gravity. However, experimental evidence of this mechanism remains scarce. This study tested predictions of a positive torque feedback mechanism for standing balance, specifically that differences between a "reference" torque and actual torque are self-amplified, causing the system to generate additional torque.

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During unperturbed bipedal standing, postural control is governed primarily by subcortical and spinal networks. However, it is unclear if cortical networks begin to play a greater role when stability is threatened. This study investigated how initial and repeated exposure to a height-related postural threat modulates cortical potentials time-locked to discrete centre of pressure (COP) events during standing.

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Implicit sensorimotor adaptation keeps our movements well-calibrated amid changes in the body and environment. We have recently postulated that implicit adaptation is driven by a perceptual error: the difference between the desired and perceived movement outcome. According to this perceptual re-alignment model, implicit adaptation ceases when the perceived movement outcome - a multimodal percept determined by a prior belief conveying the intended action, the motor command, and feedback from proprioception and vision - is aligned with the desired movement outcome.

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During reaching and grasping movements tactile processing is typically suppressed. However, during a reception or catching task, the object can still be acquired but without suppressive processes related to movement execution. Rather, tactile information may be facilitated as the object approaches in anticipation of object contact and the utilization of tactile feedback.

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We investigated the impairment of position sense associated with muscle fatigue. In , participants performed learned eccentric extension (22°/s) movements of the elbow as the arm was pulled through the horizontal plane without vision of the arm. They opened their closed right hand when they judged it to be passing through a target.

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Threats to stability elicit context-specific changes in balance control; however, the underlying neural mechanisms are not fully understood. Previous work has speculated that a shift toward greater supraspinal control may contribute to threat-related balance changes. This study investigated how neural correlates of cortical and subcortical control of balance were affected by initial and repeated exposure to a height-related postural threat.

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Mechanical muscle tendon vibration activates multiple sensory receptors in the muscle and tendon. In particular, tendon vibration tends to activate the Ia afferents the strongest, but also will activate group II and Ib afferents. This activation can cause three main effects in the central nervous system: proprioceptive illusions, tonic vibration reflexes, and suppression of the stretch response.

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Article Synopsis
  • Human balance relies on the nervous system's ability to estimate self-motion for detecting and responding to unexpected movements, which involves adjustments for sensory and motor delays.
  • A robotic system was used to simulate standing balance and introduce these delays, which initially caused instability and increased uncertainty in participants' balance perceptions.
  • After training, participants adapted to the delays, improving their balance by linking sensory feedback with their motor commands, resulting in a partial return of vestibular contributions to a more stable state.
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Goal-directed reaches are modified based on previous errors experienced (i.e., offline control) and current errors experienced during movement execution (i.

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Constraining the degrees of freedom simplifies the coordinative challenge of bimanual asymmetric movements. This, however, comes at the cost of increased processing demands during movement preparation, referred to as the bimanual asymmetric cost. The goal of the present study was to further investigate information processing of the bimanual asymmetric cost with the response priming technique.

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The long-latency "reflexive" response (LLR) following an upper limb mechanical perturbation is generated by neural circuitry shared with voluntary control. This feedback response supports many task-dependent behaviors and permits the expression of goal-directed corrections at latencies shorter than voluntary reaction time. An extensive body of literature has demonstrated that the LLR shows flexibility akin to voluntary control, but it has not yet been tested whether instruction-dependent LLR changes can also occur in the absence of an overt voluntary response.

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It is well known that increasing the complexity of the required response results in a corresponding increase in simple reaction time (RT). This "response complexity effect" has typically been attributed to increased time required to prepare some aspect of the response; however, most studies examining the response complexity effect have used an unpredictable foreperiod, which does not allow for optimal preparation to occur. Thus, it is conceivable that response complexity effects are influenced by an inability to predict the occurrence of the go-signal.

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Human movements are remarkably adaptive. We are capable of completing movements in a novel visuomotor environment with similar accuracy to those performed in a typical environment. In the current study, we examined if the control processes underlying movements under typical conditions were different from those underlying novel visuomotor conditions.

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Postural threat decreases center of pressure displacements yet increases the magnitude of movement-related conscious sway perception during quiet standing. It is unknown how these changes influence perception of whole body movement during dynamic stance. The aim of this study was to examine how postural threat influences whole-body movements and conscious perception of these movements during continuous pseudo-random support surface perturbations to stance.

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Each cerebral hemisphere primarily controls and receives sensory input with regard to the contralateral hand. In the disconnected brain (split-brain), when the hands are uncrossed, direct visual access to each hand is available to the controlling (contralateral) hemisphere. However, when a hand crosses the midline, visual and tactile information regarding the hand are presented to different hemispheres.

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A powerful tool in motor behavior research is trajectory analysis of discrete goal-directed pointing movements. The purpose of the present analysis was to estimate the minimum number of trials per participant required to achieve the conventional level of reliability for trajectory analysis. We analyzed basic measurements of movement and three common methods of trajectory analysis within the framework of generalizability theory.

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When we move, our ability to detect tactile events on the moving limb is reduced (e.g., movement-related tactile suppression).

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Perturbations delivered to the upper limbs elicit reflexive responses in stretched muscle at short- (M1: 25-50 ms) and long- (M2: 50-100 ms) latencies. When presented in a simple reaction time (RT) task, the perturbation can also elicit a preprogrammed voluntary response at a latency (< 100 ms) that overlaps the M2 response. This early appearance of the voluntary response following a proprioceptive stimulus causing muscle stretch is called a triggered reaction.

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Movement preparation of bimanual asymmetric movements takes more time than bimanual symmetric movements in choice reaction-time conditions. This bimanual asymmetric cost may be caused by increased processing demands on any stage of movement preparation. The authors tested the contributions of each stage of movement preparation to the asymmetric cost by using the additive factors method.

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When a two-choice "Simon task" is distributed between two people, performance in the shared go/no-go task resembles performance in the whole task alone. This finding has been described as the joint Simon effect (JSE). Unlike the individual go/no-go task, not only is the typical joint Simon task shared with another person, but also the imperative stimuli dictate whose turn it is to respond.

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The current study examined the processes involved in the preparation of sequencing and timing initiation for multi-component responses. In two experiments, participants performed a reaction time (RT) task involving a three key-press sequence with either a simple (isochronous) or complex (non-isochronous) timing structure. Conditions involved a precue that provided information about all features of the movement (simple RT), no features of the movement (choice RT), sequencing only, or timing structure only.

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