Romeo Chua

Government of British Columbia, Canada, Vancouver, British Columbia, Canada

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Publications (145)358.11 Total impact

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    ABSTRACT: Movement preparation of bimanual asymmetric movements is longer than bimanual symmetric movements in choice reaction time conditions, even when movements are cued directly by illuminating the targets (Blinch et al. in Exp Brain Res 232(3):947-955, 2014). This bimanual asymmetric cost may be caused by increased processing demands on response programming, but this requires further investigation. The present experiment tested the demands on response programming for bimanual movements by temporally separating the preparation of each arm. This was achieved by precuing the target of one arm before the imperative stimulus. We asked: What was prepared in advance when one arm was precued? The answer to this question would suggest which process causes the bimanual asymmetric cost. Advance movement preparation was examined by comparing reaction times with and without a precue for the left target and by occasionally replacing the imperative stimulus with a loud, startling tone (120 dB). A startle tone releases whatever movement is prepared in advance with a much shorter reaction time than control trials (Carlsen et al. in Clin Neurophysiol 123(1):21-33, 2012). Participants made bimanual symmetric and asymmetric reaching movements in simple and 2-choice reaction time conditions and a condition with a precue for the left target. We found a bimanual asymmetric cost in 2-choice conditions, and the asymmetric cost was significantly smaller when the left target was precued. These results, and the results from startle trials, suggest (1) that the precued movement was not fully programmed but partially programmed before the imperative stimulus and (2) that the asymmetric cost was caused by increased processing demands on response programming. Overall, the results support the notion that bimanual movements are not the sum of two unimanual movements; instead, the two arms of a bimanual movement are unified into a functional unit. When one target is precued, this critical unification likely occurs during response programming.
    Experimental Brain Research 04/2015; DOI:10.1007/s00221-015-4266-0 · 2.17 Impact Factor
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    ABSTRACT: Objective: To use transcranial magnetic stimulation and electromyography to assess the potential for preserved function in the abdominal muscles in individuals classified with motor-complete spinal cord injury above T6. Subjects: Five individuals with spinal cord injury (C5-T3) and 5 able-bodied individuals. Methods: Transcranial magnetic stimulation was delivered over the abdominal region of primary motor cortex during resting and sub-maximal (or attempted) contractions. Surface electromyography was used to record motor-evoked potentials as well as maximal voluntary (or attempted) contractions in the abdominal muscles and the diaphragm. Results: Responses to transcranial magnetic stimulation in the abdominal muscles occurred in all spinal cord injury subjects. Latencies of muscle response onsets were similar in both groups; however, peak-to-peak amplitudes were smaller in the spinal cord injury group. During maximal voluntary (or attempted) contractions all spinal cord injury subjects were able to elicit electromyography activity above resting levels in more than one abdominal muscle across tasks. Conclusion: Individuals with motor-complete spinal cord injury above T6 were able to activate abdominal muscles in response to transcranial magnetic stimulation and during maximal voluntary (or attempted) contractions. The activation was induced directly through corticospinal pathways, and not indirectly by stretch reflex activations of the diaphragm. Transcranial magnetic stimulation and electromyography measurements provide a useful method to assess motor preservation of abdominal muscles in persons with spinal cord injury.
    Journal of Rehabilitation Medicine 12/2014; 47(2). DOI:10.2340/16501977-1901 · 1.90 Impact Factor
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    ABSTRACT: Symmetric, target-directed, bimanual movements take less time to prepare than asymmetric movements (Diedrichsen et al. in Cerebral Cortex 16(12):1729-1738, 2006; Heuer and Klein in Psychol Res 70(4):229-244, 2006b). The preparation savings for symmetric movements may be related to the specification of symmetric amplitudes, target locations, or both. The goals of this study were to determine which symmetric movement parameters facilitate the preparation of bimanual movements and to compare the size of the facilitation for different parameters. Thirty participants performed bimanual reaching movements that varied in terms of the symmetry/asymmetry of starting locations, movement amplitudes, and target locations. Reaction time savings were examined by comparing movements that had one symmetric parameter (and two asymmetric parameters) to movements with all asymmetric parameters. We observed significant savings (~10 ms) for movements with symmetric amplitudes and movements with symmetric target locations. Reaction time costs were examined by comparing movements that had two asymmetric parameters (and one symmetric parameter) to movements with all symmetric parameters. We observed significant reaction time costs (~13 ms) for all movements with asymmetric amplitudes. These results suggest that movement preparation is facilitated when amplitudes or target locations are symmetric and that movement preparation suffers interference when amplitudes are asymmetric. The relative importance of the three parameters to movement preparation, from most to least important, is movement amplitudes, target locations, and then starting locations. Interference with asymmetric amplitudes or target locations may be caused by cross-talk between concurrent processes of parameter specification during response programming.
    Psychological Research 11/2014; DOI:10.1007/s00426-014-0624-y · 2.47 Impact Factor
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    ABSTRACT: To further our understanding of the role of the motor system in comprehending action-related sentences, we compared action experts (athletes) to visual experts (fans) and novices when responding with an action-specific effector (either hand or foot). These conditions allowed inferences about the degree and specificity of embodiment in language comprehension. Ice hockey players, fans and novices made speeded judgments regarding the congruence between an auditorily presented sentence and a subsequently presented picture. Picture stimuli consisted of either hockey or everyday items. Half of these pictures 'matched' the action implied in the preceding sentence. Further, the action in these images involved either primarily the hand or the foot. For everyday items, action-matched items were responded to faster than action-mismatched items. However, only the players and fans showed the action-match effect for hockey items. There were no consistent effector-stimuli compatibility effects, nor skill-based interactions with compatibility, suggesting that the action-match effect was not based on motor ability per se, but rather a construction of the action based on knowledge or visual experience with the hockey related sentences.
    Acta psychologica 05/2014; 150C:61-68. DOI:10.1016/j.actpsy.2014.04.005 · 2.19 Impact Factor
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    ABSTRACT: The rapid release of prepared movements by a loud acoustic stimulus capable of eliciting a startle response has been termed the StartReact effect (Valls-Solé et al., 1999), and premotor reaction times (PMTs) of <70 ms are often observed. Two explanations have been given for these short latency responses. The subcortical storage and triggering hypothesis suggests movements that can be prepared in advance of a “go” signal are stored and triggered from subcortical areas by a startling acoustic stimulus (SAS) without cortical involvement. Alternatively, it has been hypothesized that the SAS can trigger movements from cortical areas through a faster pathway ascending from subcortical structures. Two experiments were designed to examine the possible role of primary motor cortex in the StartReact effect. In Experiment 1, we used suprathreshold transcranial magnetic stimulation (TMS) during the reaction time (RT) interval to induce a cortical silent period in the contralateral primary motor cortex (M1). Thirteen participants performed 20° wrist extension movements as fast as possible in response to either a control stimulus (82dB) or SAS (124 dB). PMTs for startle trials were faster than control trials, while TMS significantly delayed movement onset compared to No TMS or Sham TMS conditions. In Experiment 2, we examined the StartReact effect in a highly cortically represented action involving speech of a consonant-vowel (CV) syllable. Similar to previous work examining limb movements, a robust StartReact effect was found. Collectively, these experiments provide evidence for cortical (M1) involvement in the StartReact effect.
    Neuroscience 03/2014; DOI:10.1016/j.neuroscience.2014.03.041 · 3.33 Impact Factor
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    ABSTRACT: The goal of this study was to determine the process or processes most likely to be involved in reaction-time costs for spatially cued bimanual reaching. We used reaction time to measure the cost of bimanual symmetric movements compared to unimanual movements (a bimanual symmetric cost) and the cost for bimanual asymmetric movements compared to symmetric movements (a bimanual asymmetric cost). The results showed that reaction times were comparable for all types of movements in simple reaction time; that is, there was neither a bimanual symmetric cost nor an asymmetric cost. Therefore, unimanual, bimanual symmetric, and bimanual asymmetric movements have comparable complexity during response initiation. In choice conditions, there was no bimanual symmetric cost but there was a bimanual asymmetric cost, indicating that the preparation of asymmetric movements is more complex than symmetric movements. This asymmetric cost is likely the result of interference during response programming.
    Experimental Brain Research 03/2014; DOI:10.1007/s00221-013-3807-7 · 2.17 Impact Factor
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    ABSTRACT: There is very little consensus regarding the mechanisms underlying postural control. While some theories suggest that posture is controlled at lower levels (i.e. brainstem and spinal cord), other theories have proposed that upright stance is controlled using higher centres including the motor cortex. In the current investigation, we used corticomuscular coherence to investigate the relationship between cortical and shank muscle activity during conditions of unrestricted and restricted postural sway. Participants were instructed to stand as still as possible in an apparatus which allowed the COM to move freely ("Unlocked") or to be stabilized ("Locked") without subject awareness. EEG (Cz) and EMG (soleus, lateral/medial gastrocnemii) were collected and used to estimate CMC over the Unlocked and Locked periods. Confirming our previous results, increases in COP displacements were observed in 9 of 12 participants in the Locked compared to Unlocked condition. Across these 9 participants, CMC was low or absent in both the Unlocked and Locked conditions. The results from the current study suggest that this increase is not associated with an increase in the relationship between cortical and shank muscle activities. Rather, it may be that increases in COP displacement with locking are mediated by subcortical structures as a means of increasing sway to provide the central nervous system (CNS) with a critical level of sensory information.
    Journal of Neurophysiology 02/2014; 111(9). DOI:10.1152/jn.00853.2012 · 3.04 Impact Factor
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    ABSTRACT: The present study was designed to investigate the mechanism associated with dual-task interference in a psychological refractory period (PRP) paradigm. We used a simple reaction time paradigm consisting of a vocal response (R1) and key-lift task (R2) with a stimulus onset asynchrony (SOA) between 100ms and 1500ms. On selected trials we implemented a startling acoustic stimulus concurrent with the second stimulus to determine if we could involuntarily trigger the second response. Our results indicated that the PRP delay in the second response was present for both control and startle trials at short SOAs, suggesting the second response was not prepared in advance. These results support a response preparation bottleneck and can be explained via a neural activation model of preparation. In addition, we found that the reflexive startle activation was reduced in the dual-task condition for all SOAs, a result we attribute to prepulse inhibition associated with dual-task processing.
    Acta psychologica 09/2013; 144(3):481-487. DOI:10.1016/j.actpsy.2013.08.005 · 2.19 Impact Factor
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    ABSTRACT: Postural responses (PR) to a balance perturbation differ between the first and subsequent perturbations. One explanation for this first trial effect (FTE) is that perturbations act as startling stimuli, that initiate a generalized startle response (GSR) as well as the PR. Startling stimuli, such as startling acoustic stimuli (SAS), are known to elicit GSRs , as well as a StartReact effect, in which prepared movements are initiated earlier by a startling stimulus.. In this study, a StartReact effect paradigm was used to determine if balance perturbations can also act as startle stimuli. Subjects completed two blocks of simple reaction time trials involving wrist extension to a visual imperative stimulus (IS). Each block included 15 CONTROL trials, that involved a warning cue and subsequent IS, followed by 10 repeated TEST trials, where either a SAS (TESTSAS) or a toes-up support-surface rotation (TESTPERT) was presented coincident with the IS. StartReact effects were observed during the first trial in both TESTSAS and TESTPERT conditions as evidenced by significantly earlier wrist movement and muscle onsets compared to CONTROL. Likewise, StartReact effects were observed in all repeated TESTSAS and TESTPERT trials. In contrast, GSR responses in SCM, and PRs were large in the first trial, but significantly attenuated over repeated presentation of the TESTPERT trials. Results suggest that balance perturbations can act as startling stimuli. Thus, FTEs are likely PRs which are super-imposed with a GSR, that is initially large, but habituates over time with repeated exposure to the startling influence of the balance perturbation.
    Journal of Neurophysiology 08/2013; 110(9). DOI:10.1152/jn.00766.2012 · 3.04 Impact Factor
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    ABSTRACT: Muscles involved in rapid, targeted movements about a single-joint often display a triphasic (agonist - antagonist - agonist) electromyographic (EMG) pattern. Early work using movement perturbations suggested that for short movements, the entire EMG pattern was prepared and initiated in advance (Wadman et al. 1979), whereas more recent TMS evidence indicates that the ANT may be programmed separately (MacKinnon and Rothwell 2000) with execution of the bursts occurring serially (Irlbacher et al. 2006). The purpose of the current study was to investigate the generation of triphasic EMG bursts for movements of different amplitudes. In Experiment 1, participants performed rapid elbow extension movements to 20° and 60° targets and on some trials, a startling acoustic stimulus (SAS), which is thought to trigger prepared motor commands at short latency, was delivered at the onset of AG1. For short movements, this perturbation elicited ANT and AG2 early, suggesting the agonist and antagonist bursts may have been programmed independently. In contrast, the same manipulation did not disrupt EMG timing parameters for the long movements, raising the possibility that ANT and AG2 were not fully programmed in advance of movement onset. In Experiment 2, a SAS was delivered later in the movement which produced early onset of both ANT and AG2. We propose that the triphasic pattern is executed serially but believe the trigger signal for initiating the ANT burst occurs not in relation to the AG1 burst, but rather in close temporal proximity to the expected onset of ANT.
    Journal of Neurophysiology 08/2013; 110(9). DOI:10.1152/jn.00888.2012 · 3.04 Impact Factor
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    ABSTRACT: Standing balance is often threatened in everyday life. These threats typically involve scenarios where either the likelihood or the consequence of falling is higher than normal. When cats are placed in these scenarios they respond by increasing the sensitivity of muscle spindles imbedded in the leg muscles, presumably to increase balance-relevant afferent information available to the nervous system. At present, it is unknown if humans also respond to such postural threats by altering muscle spindle sensitivity. Here we present two studies that probed the effects of postural threat on spinal stretch reflexes. In Study 1 we manipulated the threat associated with an increased consequence of a fall by having subjects stand at the edge of an elevated surface (3.2 m). In Study 2 we manipulated threat by increasing the likelihood of a fall by occasionally tilting the support surface on which subjects stood. In both scenarios we used Hoffmann (H-) and tendon stretch (T-) reflexes to probe the spinal stretch reflex circuit of the soleus muscle. We observed increased T-reflex and unchanged H-reflex amplitudes in both threat scenarios. These results suggest that the synaptic state of the spinal stretch reflex is unaffected by postural threat, and that therefore the muscle spindles activated in the T-reflexes must be more sensitive in the threatening conditions. We propose that this increase in sensitivity may function to satisfy the conflicting needs to restrict movement with threat, while maintaining a certain amount of sensory information related to postural control.
    Journal of Neurophysiology 05/2013; 110(4). DOI:10.1152/jn.00065.2013 · 3.04 Impact Factor
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    ABSTRACT: We asked whether the influence of an invisible prime on movement is dependent on conscious movement expectations. Participants reached to a central target, which triggered a directional prime-mask arrow sequence. Participants were instructed that the visible arrows (masks) would most often signal a movement modification in a specific (biased) direction. Kinematic analyses revealed that responses to the visible mask were influenced by participants' intentional bias, as movements were fastest when the more probable mask was displayed. In addition, responses were influenced by the invisible prime without regard to its relationship to the more probable mask. Analysis of the time of initial trajectory modifications revealed that both primes influenced responses in a similar manner after accounting for participants' bias. These results imply that invisible stimuli automatically activate their associated responses and that unconscious priming of the motor system is insensitive to the conscious expectations of the participant making the pointing movements.
    Consciousness and Cognition 05/2013; 22(3):716-728. DOI:10.1016/j.concog.2013.04.011 · 2.31 Impact Factor
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    ABSTRACT: Previous research has shown that when the COM is stabilized without participant awareness, COP displacements increase. This finding suggests that postural sway under normal conditions may be exploratory and used as a means of acquiring sensory information. However, based on the theory that posture is controlled using internal models, it could be argued that increases in COP displacement reflect errors that arise as the central nervous system attempts to adapt the internal model used to control posture to the new conditions. The current study provided an explicit verbal cue to the participants indicating how and when COM stabilization would occur. Based on evidence suggesting that explicit verbal cues can reduce errors when the dynamics of the task are altered, we hypothesized that when participants were aware of COM stabilization, COP displacements would be reduced. However, we found that anterior-posterior COP displacements increased independent of cueing, suggesting that increases in COP displacements with locking were not the result of an attempt to adapt the internal model of postural control. The results provide further support for an exploratory role of postural sway.
    Gait & posture 04/2013; 38(4). DOI:10.1016/j.gaitpost.2013.03.012 · 2.30 Impact Factor
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    ABSTRACT: Vestibular information is one of the many sensory signals used to stabilize the body during locomotion. When locomotor velocity increases the influence of these signals appears to wane. It is unclear whether vestibular signals are globally attenuated with velocity or are influenced by factors such as whether a muscle is contributing to balance control. Here we investigate how vestibular sensory signals influence muscles of the leg during locomotion and what causes their attenuation with increasing locomotor velocity. We hypothesized that a) vestibular signals influence the activity of all muscles engaged in the maintenance of medio-lateral stability during locomotion and b) increases in both cadence and velocity would be associated with attenuation of these signals. We used a stochastic vestibular stimulus and recorded electromyographic signals from muscles of the ankle, knee and hip. Participants walked using two cadences (52 and 78 steps/min and two walking velocities (0.4 and 0.8 m/s). We observed phase-dependent modulation of vestibular influence over ongoing muscle activity in all recorded muscles. Within a stride, reversals of the muscle responses were observed in the biceps femoris, tibialis anterior and rectus femoris. Vestibular-muscle coupling decreases with increases in both cadence and walking velocity. These results show that the observed vestibular-suppression is muscle and phase dependent. We suggest that the phase- and muscle-specific influence of vestibular signals on locomotor activity is organized according to each muscle's functional role in body stabilization during locomotion.
    Journal of Neurophysiology 04/2013; 110(1). DOI:10.1152/jn.00843.2012 · 3.04 Impact Factor
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    ABSTRACT: What information is necessary for the motor system to adapt its behaviour? Visual hand-to-target error provides salient information about reach performance, but can learning proceed without this information? We investigated adaptation to an unperceived target perturbation under visual open-loop conditions. Participants looked and reached, without any vision of their hand, to a target that jumped rightward at saccade onset (Perturbation condition) or remained stationary throughout the trial (Stationary condition). The target jump in the Perturbation condition was tied to the saccade, such that participants were unaware that it had occurred. Each type of exposure was followed by a posttest, in which participants reached to a target that disappeared at saccade onset. In the posttest, participants reached farther following exposure to the perturbation than they did following exposure to the stationary target, indicating that participants had learned from systematic exposure to the jump. These findings imply that online error induces motor learning, even when participants receive no visual information about their performance.
    Acta psychologica 04/2013; 143(1):129-135. DOI:10.1016/j.actpsy.2013.03.002 · 2.19 Impact Factor
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    ABSTRACT: Covert forms of practice, such as observation and imagery, have been shown to involve neurophysiological activation of the motor system, and a functional equivalence between covert and overt processes involved in action execution has been proposed (Jeannerod, 2001). We used a startling acoustic stimulus (SAS), which has been shown to trigger prepared movements involuntarily at short latencies via an increase in cortical activation, to probe the similarity of these processes and elicit movement responses in imagery and observation trials. Startle trials were interspersed with control trials while participants (n=16) performed or imagined a right hand key lift or observed a model perform the key lift. During physical movement trials, intended movements were triggered by the SAS at a short latency (RT=78ms) in comparison to control trials (RT=110ms). During imagery and observation, unimanual partial movements (assessed by force change and muscle activation) were elicited by the SAS, providing novel behavioural evidence for a functional similarity between covert and overt movement preparation processes. Examination of the magnitude of the reflexive startle response (an index of motor preparation) during imagery and observation also revealed similarities to physical movement trials. We conclude that covert and overt movements involve similarities in motor preparation and neural pathways, and propose that movements do not normally occur during imagery and observation due to low level neural activation.
    Neuropsychologia 01/2013; DOI:10.1016/j.neuropsychologia.2013.01.016 · 3.45 Impact Factor
  • Research quarterly for exercise and sport 01/2013; 77(3):396-400. DOI:10.1080/02701367.2006.10599374 · 1.26 Impact Factor
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    ABSTRACT: When the target of a goal-directed reach changes location, people normally respond rapidly and automatically to the target shift. Here, we investigate whether explicit knowledge about a moving target (knowing whether a location change is likely/unlikely) improves responsiveness, with the goal of understanding top-down effects on real-time reaching. In Experiment 1, we presented participants with pre-cues that indicated a 20 or 80 % likelihood of a target perturbation on that trial. When participants made pro-pointing responses to the target perturbations, their online response occurred later for 20 % trials than for 80 % trials, but this effect may have been due to suppression of the online response on 20 % trials, rather than enhancement of the response on 80 % trials. In Experiment 2, we presented participants with 50 and 100 % likelihood pre-cues, and observed no shortening of the latency on 100 % trials compared to 50 % trials, which suggests that expectation does not enhance the automatic response to a perturbation. However, we did observe more vigorous responses to the perturbation on the 100 % trials, and this contributed to shorter movement times relative to the 50 % trials. We also examined, in Experiment 2, whether prior knowledge about the direction of the target perturbation would shorten the latency of the online response, but we did not observe any reduction in latency. In sum, the onset of the automatic response appears to be suppressible, but not augmentable by top-down input. The possibility that the forcefulness of the automatic response is modifiable by expectation is examined, but not resolved.
    Experimental Brain Research 01/2013; DOI:10.1007/s00221-013-3401-z · 2.17 Impact Factor
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    ABSTRACT: It is remarkable that the movement time of a goal-directed movement, the result of complex coordination in the nervous system, can be predicted by a simple mathematical equation. That equation is Fitts' law, and it is one of only a few laws that capture human motor performance. It has recently been shown that reaches to targets with placeholders modulate Fitts' law (e.g. Adam et al. in Psychol Sci 17(9):794-798, 2006). The purpose of this study was to further test whether the modulation to Fitts' law is a result of processes related to movement preparation or movement execution. Preparation and control processes were isolated with trajectory analysis; specifically, the durations of the primary submovement and the secondary submovement were selected to reflect the preparation and control processes, respectively. The time available for movement preparation was also manipulated by precuing the target in some blocks. We found that the modulation to Fitts' law in total movement time with target placeholders occurred during the secondary submovement, suggesting that control processes were the locus of the modulation. However, extending the duration of preparation with a precue eliminated the modulation in total movement time, which suggests that preparation processes were the locus of the modulation. Based on these results, it is premature to isolate unequivocally the modulation to either preparation or control processes. The modulation to Fitts' law during the secondary submovement presents the possibility that facilitated online control may contribute to the modulation.
    Experimental Brain Research 12/2012; 223(4):505-15. DOI:10.1007/s00221-012-3277-3 · 2.17 Impact Factor

Publication Stats

3k Citations
358.11 Total Impact Points

Institutions

  • 2002–2014
    • Government of British Columbia, Canada
      Vancouver, British Columbia, Canada
    • Arizona State University
      Phoenix, Arizona, United States
  • 2000–2014
    • University of British Columbia - Vancouver
      • School of Kinesiology
      Vancouver, British Columbia, Canada
  • 1991–2010
    • Simon Fraser University
      • Department of Psychology
      Burnaby, British Columbia, Canada
  • 2008
    • University of Portsmouth
      Portsmouth, England, United Kingdom
  • 1997–2001
    • University of Alberta
      • Faculty of Physical Education and Recreation
      Edmonton, Alberta, Canada
  • 1993–2001
    • McMaster University
      • Department of Kinesiology
      Hamilton, Ontario, Canada
  • 1998
    • University of Waterloo
      Ватерлоо, Ontario, Canada