Biomedical subjects

Romeo Chua

Publications and source records attributed to Romeo Chua.

At least 37 records · Page 2Linked to original sources

PubMed2005

Assessing vestibular contributions during changes in gait trajectory.

Displacing prisms and galvanic stimulation were used to examine visual-vestibular interactions during target-directed gait. Participants walked towards a wall 6 m away. After taking four steps, a target on the wall, located directly in front or to the right of the participant, was illuminated. Participants continued walking towards the target. Galvanic vestibular stimulation was triggered at either gait initiation, a step before the potential turn, or at target illumination. Although the visual and vestibular perturbations significantly altered gait trajectory, the greatest interaction occurred when galvanic stimulation was triggered one step before the target appeared. This implies an increase in the weighting of vestibular inputs just before turning to prepare for the potential change in direction.

Adult↗

PubMed2005

Evaluation of scanning methodology in bimanual coordination.

A major component of a dynamical paradigm involves a "scanning" procedure in an attempt to determine an individual's intrinsic coordination tendencies before learning, as well as subsequent changes in the coordination landscape after practice. The purpose of the present study was to evaluate two methods of the scanning procedure. Scans were performed before and after 75 trials of a 90 degrees bimanual-coordination pattern and were compared with early and late acquisition trials. Four groups of participants performed scanning and acquisition trials using a combination of either concurrent visual feedback in the form of Lissajous figures, paced by an auditory metronome, or visual metronomes in the form of flashing stimuli. Analyses revealed that all groups improved performance of the 90 degrees pattern with practice. As predicted by the theory of practice specificity, scanning via the same method as acquisition appears to be valid. Scanning via Lissajous figures when the acquisition procedure was flashing squares was also found to be valid, but not the opposite condition. Reasons for this unidirectional transfer are given with these results suggesting that the sensitivity of a given scanning method might be influenced by the method of acquiring the coordination pattern.

Acoustic Stimulation↗

PubMed2004

What the hand can't tell the eye: illusion of space constancy during accurate pointing.

When we press an elevator button or pick up a coffee cup, different visual information is used to guide our reach and to form our conscious experience of these objects. But can the information guiding our hand be brought into awareness? The fact that we can see and feel our own hand in action suggests that it might be possible. However, the dual visual systems theory claims that on-line control of movement is governed by the dorsal stream of visual processing, which is largely unconscious. Two experiments are presented as strong tests of the hypothesis that the visual information guiding on-line pointing in healthy human adults is inaccessible for conscious report. Results show that participants are incapable of consciously accessing the information used in pointing, even though they can see and feel their hands in action and accurate performance depends on it.

Biomechanical Phenomena↗

PubMed2004

Can prepared responses be stored subcortically?

Quick voluntary responses to environmental stimuli are required of people on a daily basis. These movements have long been thought to be controlled via cortical loops involving processing of the stimulus and generation of a suitable response. Recent experiments have shown that in simple reaction time (RT) tasks, the appropriate response can be elicited much earlier (facilitated) when the "go" signal is replaced by a startling (124 dB) auditory stimulus. In the present experiment we combined a startling acoustic stimulus with an established RT paradigm that involved simple and choice RT. In a simple RT condition the prepared voluntary response was elicited at very short latencies following the startle. However, when cortical processing was required prior to responding (choice RT task), the startle did not facilitate the voluntary response, and gave rise to more movement production errors. Since movements requiring ongoing cortical processing following the stimulus are not facilitated by startle, it is unlikely that the startle facilitation is due to increased neural activation. In contrast, it appears more likely that the startle acts as an early trigger for subcortically stored prepared movements since movements that are prepared in advance can be initiated at such short latencies (<60 ms).

Acoustic Stimulation↗

PubMed2004

Galvanic vestibular stimulation alters the onset of motor unit discharge.

We have previously shown that galvanic vestibular stimulation (GVS) can modulate the amplitude of the passive soleus H-reflex. This study examined whether the response resulted from a general change in excitability of the motoneuron pool or a specific modulation of individual motor units (MUs). Subjects performed slow isometric plantarflexor actions in a prone lying and kneeling position until the discharge of a single gastrocnemius MU was detected. During randomly selected trials, a 1-mA bipolar, binaural galvanic stimulus was triggered just prior to the start of plantarflexor activity. With the knee extended and the medial gastrocnemius (MG) at a long muscle length, GVS did not have an effect on MU activity. However, when the knee was flexed and the MG muscle was shortened, GVS significantly modified the onset of activation and the initial firing frequency of MUs. This may reflect a change in the gain of the presynaptic inhibitory mechanisms that act on the motoneuron pool once a muscle reaches a shortened, nonoptimal force-producing length. Thus, GVS may provide an important research tool for activating descending vestibulospinal pathways that act on lower-limb motoneurons and may be applied to test the integrity of the spinal cord.

Adult↗

PubMed2004

Prepared movements are elicited early by startle.

A startle stimulus has been shown to elicit a ballistic response in a reaction time (RT) task at very short latencies without involvement of the cerebral cortex (J. Valls-Sole, J. C. Rothwell, F. Gooulard, G. Cossu, & E. Munoz, 1999). The present authors examined the nature of the startle response. A simple RT task was used in which 8 participants performed arm extension movements to 3 target distances (20 degrees, 40 degrees, and 60 degrees ) in a blocked design. An unpredictable startling acoustic stimulus (124 dB) replaced the imperative stimulus in certain trials. The authors verified the presence of a startle response independent from the prepared response by observing electromyographic (EMG) activity in sternocleidomastoid and orbicularis oculi muscles. Findings indicated that when the participant was startled, the intended voluntary response was produced at significantly shorter response latencies. Furthermore, the kinematic variables of the observed response during startle trials for all 3 target distances were mostly unchanged. The EMG characteristics of the responses were not modified, indicating that the response produced was indeed the prepared and intended response.

Adult↗

PubMed2004

Inhibiting prepared and ongoing responses: is there more than one kind of stopping?

Inhibiting movements has been investigated widely using the countermanding (stop signal) paradigm. Although it has been assumed that response inhibition, as measured by the countermanding task, generalizes to all forms of stopping, this has never been tested. In the present study, stopping performance in the countermanding paradigm was compared with stopping performance in a new paradigm in which a continuous-tracking task was used. Although stimulus presentations were matched across paradigms, the two tasks differed in the type of stopping required. In the countermanding paradigm, response inhibition latency was measured prior to response execution-this is, it was inferred from the successful withholding of a go response. In the new paradigm, response inhibition was carried out after response execution-that is, it was measured as the time to begin stopping a continuous tracking response. Results indicated that stopping latencies between the two paradigms were highly correlated, providing strong evidence that stopping an unexecuted response engages the same mechanisms as stopping an ongoing response.

Adult↗

PubMed2003

Relative contributions of visual and vestibular information on the trajectory of human gait.

Seven healthy individuals were recruited to examine the interaction between visual and vestibular information on locomotor trajectory during walking. Subjects wore goggles that either contained a clear lens or a prism that displaced the visual scene either 20 degrees to the left or right. A 5-s bipolar, binaural galvanic stimulus (GVS) was also applied at three times the subject's individual threshold (ranged between 1.2 to 1.5 mA). Subjects stood with their eyes closed and walked forward at a casual pace. At first heel contact, subjects opened their eyes and triggered the galvanic stimulus by foot switches positioned underneath a board. Reflective markers were placed bilaterally on the shoulders as the walking trajectory was captured using a camera mounted on the ceiling above the testing area. Twelve conditions were randomly assigned that combined four visual conditions (eyes closed, eyes open, left prism, right prism) and three GVS conditions (no GVS, GVS anode left, GVS anode right). As subjects walked forward, there was a tendency to deviate in the direction of the prisms. During GVS trials, subjects deviated towards the anode while walking, with the greatest deviations occurring with the eyes closed. However, when GVS was presented with the prisms, subjects always deviated to the side of the prisms, regardless of the position of the anode. Furthermore, the visual-vestibular conditions produced a larger lateral deviation than those observed in the prisms-only trials. This suggests that the nervous system examines the sensory inputs and takes into account the most reliable and relevant sensory input.

Adult↗

PubMed2003

Startle response is dishabituated during a reaction time task.

Recent experiments pairing a startling stimulus with a simple reaction time (RT) task have shown that when participants are startled, a prepared movement may be triggered earlier in comparison to voluntary initiation (Carlsen et al. 2003, in press; Siegmund et al. 2001; Valls-Solé et al. 1999). The use of this paradigm in experiments may provide new insights into processes that control rapid voluntary actions. However, because the startle response habituates with repeated exposure to the startling stimulus, its use in experiments may be limited. Previously Brown et al. (1991) and later Siegmund et al. (2001) noted that individuals habituate to a startling stimulus at different rates depending on the required activity level of the participant in the task. The present experiment was designed to determine the rate at which participants habituate to a startle during the completion of a RT task. Participants completed 100 trials in which an active wrist extension to a target was performed as fast as possible following an auditory tone. An unexpected 124 dB auditory startle stimulus accompanied the imperative stimulus in 20 of these trials. For the duration of the experiment, startle response electromyographic (EMG) activity continued to be produced in the sternocleidomastoid muscle (SCM) indicating that habituation was not complete after 20 startle trials. Furthermore RT in the startle condition was significantly shorter than control RT. However, findings indicate that when a measurable EMG burst in the SCM was present, RT was significantly shorter than when no SCM burst was present.

Acoustic Stimulation↗

PubMed2003

Postural and movement adaptations by individuals with a unilateral below-knee amputation during gait initiation.

The present study examined the compensatory strategies adopted by individuals with a unilateral below-knee amputation (BKA) during gait initiation. Eleven individuals with a unilateral BKA and 11 able-bodied subjects initiated gait at three step length conditions (+0, +25 and +50% of preferred step length). A lead-limb condition was also introduced, such that all participants were required to initiate gait with both their left and right limbs. For all step length and lead-limb conditions, it was found that individuals with a unilateral BKA required more time to initiate gait, as compared with the able-bodied. This increase in movement duration was attributed to the stability and movement limitations of the prosthetic limb. On the other hand, by prolonging the task duration, these individuals were also able to employ a 'horizontal impulse' strategy, whereby they could create a similar magnitude of horizontal impulse as the able-bodied without the need to apply a large magnitude of peak antero-posterior (A-P) force.

Adaptation, Physiological↗

PubMed2003

The role of video in facilitating perception and action of a novel coordination movement.

Two groups (n = 10 in each) practiced a novel, bimanual coordination pattern that was demonstrated on video. One of the groups received augmented video feedback of their own responses after each trial following a demonstration. The video-feedback group showed better performance in acquisition and retention than the no-feedback group. On error-detection tests, the video-feedback group was better able to distinguish between correct and incorrect movement patterns. The authors concluded that video feedback helps to make relative phase information salient by aiding the discrimination process. Prepractice ability on a scanning task revealed that individuals who persevered with in-phase-type movements, even though the task demands dictated otherwise, had the most difficulty determining and subsequently performing the required movement. Video feedback helped them to compensate for those difficulties.

Adult↗

PubMed2003

Stopping and restarting an unfolding action at various times.

The ability to inhibit an unfolding action is usually investigated using a stop signal (or gostop) task. The data from the stop-signal task are often described using a horse-race model whose key assumption is that each process (i.e., go, stop) exhibits stochastic independence. Using three variations of a coincident-timing task (i.e., go, gostop, and gostopgo) we extend previous considerations of stochastic independence by analysing the go latencies for prior effects of stopping. On random trials in the gostopgo task the signal sweep was paused for various times at various distances before the target. Significant increases in latency errors were reported on those trials on which the signal was paused (p <.005). Further analyses of the pause trials revealed significant effects for both the stopping interval (p <.001) and the pause interval (p <.05). Tukey post hoc analyses demonstrated increased latency errors as a linear function of the stopping interval, as expected, and decreased latency errors as a nonlinear function of the pause interval. These latter results indicate that the latencies of the go process, as reflected in the latency errors, may not exhibit stochastic independence under certain conditions. Various control mechanisms were considered in an attempt to explain these data.

Arm↗

PubMed2003

Regional variation and changes with ageing in vibrotactile sensitivity in the human footsole.

Recently there has been indirect evidence suggesting that age-related elevation in footsole vibration detection may be associated with balance and gait dysfunction. As a first step in investigating this dysfunction, the current study determined by how much plantar vibration sensation decreases as a function of age, and if change is dependent on frequency and location of vibration application. Vibration thresholds were assessed at 4 frequencies (25-400 Hz), at 55 locations, and in young and older participants. Results showed there were 3 regions of sensitivity on the footsole: the ball/medial arch, the lateral border of the foot and heel, and the toes. Thresholds for fast-adapting type I receptor (FAI)-mediated frequencies were age invariant; however, thresholds for fast-adapting type II receptor (FAII)-mediated frequencies increased with age. These changes may be one of many factors contributing to age-related changes in gait.

Adult↗

PubMed2002

Altered triggering of a prepared movement by a startling stimulus.

An experiment is reported that investigated the effects of an auditory startling stimulus on a compound movement task. Previous findings have shown that, in a targeting task, a secondary movement can be initiated based on the proprioceptive information provided by a primary movement. Studies involving the presentation of a startling stimulus have shown that in reaction time (RT) tasks, prepared ballistic movements could be released early when participants are startled. In the present study we sought to determine whether the secondary component in an ongoing movement task, once prepared, could also be triggered by a startling stimulus. Participants performed a slow active elbow extension (22 degrees /s), opening their hand when the arm passed 55 degrees of extension from the starting point. An unexpected 124 dB startle stimulus was presented 5, 25, or 45 degrees into the movement. Findings showed that, when participants were startled, the secondary component was triggered despite incongruent kinesthetic information. However, this only occurred when the startle was presented late in the primary movement. This suggests that the secondary movement was not prepared prior to task initiation, but was "loaded" into lower brain structures at some point during the movement in preparation to be triggered by the CNS. This occurred late in the movement sequence, but >/=400 ms prior to reaching the target. These findings indicate that, in addition to ballistic RT tasks, a startle can be used to probe response preparation in ongoing compound movement tasks.

Adult↗

PubMed2002

Spatial constraints in bimanual coordination: influences of effector orientation.

Two experiments are reported that examined the influence of spatial orientation of the upper limbs in bimanual coordination. In both experiments, the upper limbs were oriented in either parallel, orthogonal, or obtuse spatial configurations and participants were asked to move their limbs continuously in temporal (1:1) synchrony, prepared in either in-phase or anti-phase modes of coordination. Bimanual coordination trials in Experiment 1 were paced by a metronome at one of four frequencies (1.0, 1.5, 2.0 or 2.5 Hz). Measures of relative phase accuracy and stability both revealed that, as metronome frequency increased, in-phase coordination dominated for the parallel spatial orientation, anti-phase coordination dominated for the orthogonal spatial orientation, and neither pattern dominated for the obtuse spatial orientations. In Experiment 2, an intentional switch method replicated and extended these influences of spatial orientation. The time to voluntarily switch from an anti-phase pattern to an in-phase pattern was faster than an in-phase to anti-phase switch (confirming support for the dominance of the in-phase pattern), but this was true only for the parallel spatial orientation. The reverse was true for the orthogonal spatial orientation (i.e., faster from in-phase to anti-phase), and no difference in switch times was observed for an obtuse spatial orientation. These findings support and extend previous research regarding the influence of spatial orientation in bimanual coordination and may be attributed to the role of, and potential interactions between, egocentric, allocentric, and mechanical constraints during action.

Adult↗

PubMed2002

The role of cutaneous receptors in the foot.

Cutaneous receptors in the foot sole appear to contribute to the control of human stance and locomotion. Two approaches were undertaken to establish the characteristics of the receptors in the sole. Psychophysical vibrotactile thresholds (range 25-400 Hz) were determined across the unloaded sole in young and elderly subjects. Thresholds were lower in the ball and arch of the sole, than in the heel and toe regions. Elderly subjects demonstrated significantly elevated thresholds for high-frequency vibration. Secondly, microneurographic recordings were made from skin afferents of the unloaded sole in young subjects. Results indicated that while similar types of cutaneous receptors exist in the sole of the foot and hand, there appear to be differences in receptor density and distribution. Our results demonstrate that cutaneous afferent inputs from the foot sole provide useful information for the control of posture and locomotion.

Adult↗

PubMed2002

Optimal control strategies under different feedback schedules: kinematic evidence.

Two experiments were conducted in which participants (N = 12, Experiment 1; N = 12, Experiment 2) performed rapid aiming movements with and without visual feedback under blocked, random, and alternating feedback schedules. Prior knowledge of whether vision would be available had a significant impact on the strategies that participants adopted. When they knew that vision would be available, less time was spent preparing movements before movement initiation. Participants also reached peak deceleration sooner but spent more time after peak deceleration adjusting limb trajectories. Consistent with those findings, analysis of spatial variability at different points in the trajectory indicated that variability increased up to peak deceleration but then decreased from peak deceleration to the end of the movement.

Biomechanical Phenomena↗

PubMed2002

Bimanual coordination dynamics in adults with Down syndrome.

Previous experiments involving discrete unimanual tasks have shown that individuals with Down syndrome (DS) have auditory/verbal-motor deficits. The present study investigated unimanual and bimanual continuous perceptual-motor actions in adults with DS. Ten adults with DS, 10 typical adults, and 10 children drew continuous circles at increasing periods bimanually and unimanually with each hand. Movement was paced by either a visual or an auditory metronome. The results revealed that for circle shape and coordination measures, children and adults were more accurate with the visual metronome, whereas adults with DS were more accurate with the auditory metronome. In the unimanual tasks, adults with DS displayed hand asymmetries on spatial measures. In the bimanual task, however, adults with DS adopted an in-phase coordination pattern and stability more similar to adults than children. These results suggest that bimanual coordination in adults with DS is functioning effectively despite hand asymmetries evident in unimanual performance.

Adult↗