Whether a reduced perception of self-motion contributes to poor walking speed adaptations in older adults is unknown. In this study, speed discrimination thresholds (perceptual task) and walking speed adaptations (walking task) were compared between young (19–27 years) and young-old individuals (63–74 years), and the relationship between the performance on the two tasks was examined. Participants were evaluated while viewing a virtual corridor in a helmet-mounted display. Speed discrimination thresholds were determined using a staircase procedure. Walking speed modulation was assessed on a self-paced treadmill while exposed to different self-motion speeds ranging from 0.25 to 2 times the participants’ comfortable speed. For each speed, participants were instructed to match the self-motion speed described by the moving corridor. On the walking task, participants displayed smaller walking speed errors at comfortable walking speeds compared with slower of faster speeds. The young-old adults presented larger speed discrimination thresholds (perceptual experiment) and larger walking speed errors (walking experiment) compared with young adults. Larger walking speed errors were associated with higher discrimination thresholds. The enhanced performance on the walking task at comfortable speed suggests that intersensory calibration processes are influenced by experience, hence optimized for frequently encountered conditions. The altered performance of the young-old adults on the perceptual and walking tasks, as well as the relationship observed between the two tasks, suggest that a poor perception of visual motion information may contribute to the poor walking speed adaptations that arise with aging.
Marie-Jasmine Lalonde-Parsi and Anouk Lamontagne
Sylvain Hanneton, Svetlana Dedobbeler, Thomas Hoellinger and Agnès Roby-Brami
The study proposes a rigid-body biomechanical model of the trunk and whole upper limb including scapula and the test of this model with a kinematic method using a six-dimensional (6-D) electromagnetic motion capture (mocap) device. Large unconstrained natural trunk-assisted reaching movements were recorded in 7 healthy subjects. The 3-D positions of anatomical landmarks were measured and then compared to their estimation given by the biomechanical chain fed with joint angles (the direct kinematics). Thus, the prediction errors was attributed to the different joints and to the different simplifications introduced in the model. Large (approx. 4 cm) end-point prediction errors at the level of the hand were reduced (to approx. 2 cm) if translations of the scapula were taken into account. As a whole, the 6-D mocap seems to give accurate results, except for pronosupination. The direct kinematic model could be used as a virtual mannequin for other applications, such as computer animation or clinical and ergonomical evaluations.
Deborah L. Feltz, Norbert L. Kerr and Brandon C. Irwin
The present investigation examined the Köhler motivation gain effect in a health game using an absent partner, presented virtually. The Köhler effect occurs when an inferior team member performs a difficult task better in a team or coaction situation than one would expect from knowledge of his or her individual performance. The effect has been strongest in conjunctive task conditions in which the group’s potential productivity is equal to the productivity of its least capable member. Participants were randomly assigned to one of four conditions (individual control, coaction, additive, and conjunctive) in a 4 (conditions) × 2 (gender) factorial design and performed a series of isometric plank exercises within an exercise game. They performed the first series of five exercises alone holding each position for as long as they could, and, after a rest period, those in the partner conditions were told they would do remaining trials with a same-sex virtual partner whom they could observe during their performance. The partner’s performance was manipulated to be always superior to the participant’s. Results showed that task persistence was significantly greater in all experimental conditions than in the individual control condition. The conjunctive condition was no more motivating than either the additive or coactive conditions. Results suggest that working out with virtually present, superior partners can improve persistence motivation on exercise game tasks.
Joel R. Martin, Mark L. Latash and Vladimir M. Zatsiorsky
This study investigated the effects of modifying contact finger forces in one direction—normal or tangential—on the entire set of the contact forces, while statically holding an object. Subjects grasped a handle instrumented with finger force-moment sensors, maintained it at rest in the air, and then slowly: (1) increased the grasping force, (2) tried to spread fingers apart, and (3) tried to squeeze fingers together. Analysis was mostly performed at the virtual finger (VF) level (the VF is an imaginable finger that generates the same force and moment as the four fingers combined). For all three tasks there were statistically significant changes in the VF normal and tangential forces. For finger spreading/squeezing the tangential force neutral point was located between the index and middle fingers. We conclude that the internal forces are regulated as a whole, including adjustments in both normal and tangential force, instead of only a subset of forces (normal or tangential). The effects of such factors as EFFORT and TORQUE were additive; their interaction was not statistically significant, thus supporting the principle of superposition in human prehension.
Sukhvinder S. Obhi, Patrick Haggard, John Taylor and Alvaro Pascual-Leone
Bimanual coordination tasks form an essential part of our behaviour. One brain region thought to be involved in bimanual coordination is the supplementary motor area (SMA). We used repetitive transcranial magnetic stimulation (rTMS) at 1 Hz for 5 min to create a temporary virtual lesion of the rostral portion of the human SMA immediately prior to performance of a goal-directed bimanual coordination task. In two control conditions, participants underwent sham stimulation or stimulation over the primary motor cortex (MI). The experimental task was to open a drawer with the left hand, catch a ball with the right hand, and reinsert the ball into the drawer through an aperture just big enough for the ball to pass through, again with the right hand. Hence, the actions of one hand depend upon the actions of the other. We calculated time intervals between the successive component actions of one hand (unimanual intervals) and actions of both hands (bimanual intervals) and analyzed these intervals separately. Interestingly, none of the unimanual intervals were affected by the rTMS, but the variability of a critical bimanual interval—the time between the left hand opening the drawer and the right hand starting to move to catch the ball—was increased by rTMS over the rostral parts of the SMA. No such effect was seen following rTMS over MI or after sham rTMS. Our results suggest that the rostral parts of the SMA play an important role in aspects of functional bimanual tasks, which involve tight temporal coordination between different motor actions of the two hands.
Yongjin Hwang, Khalid Ballouli, Kevin So and Bob Heere
, whether through static advertisements, product placement, or auditory mentions ( Walsh et al., 2013 ). The least intrusive and most frequently used form of IGA is the static advertisement, particularly the virtual billboard ( King, Delfabbro, & Griffiths, 2010 ). There are growing numbers of brands that
Chad M. Killian, Christopher J. Kinder and Amelia Mays Woods
learning experiences ( Berge & Clark, 2005 ). In addition to online virtual schools and proprietary online courses for credit, there are a variety of ways schools and teachers can leverage the Internet to provide online-based learning opportunities for students. For example, popular online learning
Brigid M. Lynch, Andrea Ramirez Varela and Terry Boyle
. For example, the Council will provide members with the following: • Newsletters describing key concepts and methods and highlighting recent publications that have employed causal inference or quantitative bias analysis methods to address physical activity–related questions. • A virtual journal club
Noah X. Tocci, David R. Howell, Dai Sugimoto, Corey Dawkins, Amy Whited and Donald Bae
Coordinate System Definitions The pelvis local coordinate system was defined as follows: origin, Pelvis_Origin virtual marker; longitudinal axis, a vector extending from the Pelvis_Origin to the mid_Hip virtual marker; mediolateral axis, a vector extending from the Pelvis_Origin to the sacrum marker; and
strategy matters without operational excellence. Harvard Business Review, 95 (5), 120–128. Harnessing the Power of Virtual Fan Communities Virtual fan communities (VFCs) or online message boards are not only an important means of communication, but also a lucrative platform for advertisers and