Motor Learning Without Knowledge of Results Through the Development of a Response Recognition Mechanism

Four experiments were conducted to investigate the ability of a response recognition mechanism, developed by presenting the sensory consequences associated with the criterion movement in the absence of actual movement recall, to produce motor learning in the absence of knowledge of results (KR). In Experiments 1 and 2, a rapid linear timing task was used (10.16 cm in 100 msec), and reduction of movement error resulted over no-KR practice trials. Experiments 3 and 4 employed a slow movement-time task (750 and 1250 msec) and a linear positioning task, respectively, and no reduction of movement error occurred over the no-KR practice trials in either experiment. The ability of the response recognition mechanism to produce motor learning in the absence of KR depended upon the extent to which feedback could be used during response production.     

Obstacle Crossing Differences Between Blind and Blindfolded Subjects After Haptic Exploration

Little is known about the ability of blind people to cross obstacles after they have explored haptically their size and position. Long-term absence of vision may affect spatial cognition in the blind while their extensive experience with the use of haptic information for guidance may lead to compensation strategies. Seven blind and 7 sighted participants (with vision available and blindfolded) walked along a flat pathway and crossed an obstacle after a haptic exploration. Blind and blindfolded subjects used different strategies to cross the obstacle. After the first 20 trials the blindfolded subjects reduced the distance between the foot and the obstacle at the toe-off instant, while the blind behaved as the subjects with full vision. Blind and blindfolded participants showed larger foot clearance than participants with vision. At foot landing the hip was more behind the foot in the blindfolded condition, while there were no differences between the blind and the vision conditions. For several parameters of the obstacle crossing task, blind people were more similar to subjects with full vision indicating that the blind subjects were able to compensate for the lack of vision.     

Using token reinforcement to increase walking for adults with intellectual disabilities

The purpose of this study was to evaluate the effectiveness of token reinforcement, using an ABAB reversal design, for increasing distance walked for adults with mild to moderate intellectual disabilities at an adult day‐training center. Five participants earned tokens for walking 50‐m laps and exchanged tokens for back‐up reinforcers that had been identified through preference assessments. Token reinforcement resulted in a substantial increase from baseline in laps walked for 4 participants.     

The Effect of Cane Use on Attentional Demands During Walking

We investigated the effects of cane use, lateral walking stability, and cane use practice on attentional demands during walking. Attentional demands were assessed using dual-task methodology with a reaction time (RT) task. Sixteen healthy young subjects performed the RT task during walking, before and after cane use practice under four conditions: with/without cane use while wearing normal/unstable shoes. Among normal shoe conditions, cane use resulted in longer RTs. In contrast, RTs were similar regardless of cane use in the unstable shoe conditions. Among conditions without cane use, unstable shoes resulted in longer RTs. In contrast, RTs were similar regardless of shoe type in the cane use conditions. This study suggests that using a cane during walking requires additional attention; however, the resulting attentional demands depend on walking stability.     

Audiovisual integration increases the intentional step synchronization of side-by-side walkers

When people walk side-by-side, they often synchronize their steps. To achieve this, individuals might cross-modally match audiovisual signals from the movements of the partner and kinesthetic, cutaneous, visual and auditory signals from their own movements. Because signals from different sensory systems are processed with noise and asynchronously, the challenge of the CNS is to derive the best estimate based on this conflicting information. This is currently thought to be done by a mechanism operating as a Maximum Likelihood Estimator (MLE). The present work investigated whether audiovisual signals from the partner are integrated according to MLE in order to synchronize steps during walking. Three experiments were conducted in which the sensory cues from a walking partner were virtually simulated. In Experiment 1 seven participants were instructed to synchronize with human-sized Point Light Walkers and/or footstep sounds. Results revealed highest synchronization performance with auditory and audiovisual cues. This was quantified by the time to achieve synchronization and by synchronization variability. However, this auditory dominance effect might have been due to artifacts of the setup. Therefore, in Experiment 2 human-sized virtual mannequins were implemented. Also, audiovisual stimuli were rendered in real-time and thus were synchronous and co-localized. All four participants synchronized best with audiovisual cues. For three of the four participants results point toward their optimal integration consistent with the MLE model. Experiment 3 yielded performance decrements for all three participants when the cues were incongruent. Overall, these findings suggest that individuals might optimally integrate audiovisual cues to synchronize steps during side-by-side walking.     

Learning to Move

ABSTRACT— Locomotion—moving the body from place to place—is one of infants' greatest achievements. In addition to conquering gravity, infants must cope with variable and novel constraints on balance and propulsion. At the same time that they are learning to move, changes in infants' bodies, skills, and environments change the biomechanical constraints on movement. Recent work highlights both flexibility and specificity in infants' responses to novel and variable situations, demonstrating that infants are learning to learn as they master locomotion. Within sitting, crawling, cruising, and walking postures, experienced infants adapt their locomotor responses to the current biomechanical constraints on movement. However, what infants have learned about coping with variability and novelty in earlier-developing postures does not transfer to later-developing postures.     

Foot and shoe responsible for majority of soft tissue work in early stance of walking

Soft tissues located throughout the human body are known to perform substantial mechanical work through wobbling and deforming, particularly following foot impacts with the ground. Yet, it is not known which specific tissues in the body are responsible for the majority of the soft tissue work. The purpose of this study was to quantify how much of the soft tissue work after foot contact was due to the foot and shoe, vs. from tissues elsewhere in the body, and how this distribution of work changed with walking speed and slope. We collected ground reaction forces and whole-body kinematics while ten subjects walked at five speeds (0.8–1.6 m/s) and on seven different slopes (9 degrees downhill to 9 degrees uphill). Using a previously-published Energy-Accounting analysis, we found that the majority of the soft tissue work during early stance was due to deformation of the foot and shoe. The percentage of work did not vary significantly with speed but did vary significantly with slope. The foot and shoe were responsible for ∼60–70% of the soft tissue work during level and uphill walking, and 80–90% during downhill walking.     

Necessary condition for forward progression in ballistic walking

Ballistic walking requires an appropriate configuration of posture and velocity at toe-off to avoid backward falling. In this study, we investigated a determinant of the state of the body center of mass (COM) at the toe-off with regard to ballistic walking. We used an inverted pendulum model to represent ballistic trajectories and the necessary condition for forward progression by a simple relationship between the COM states (position and velocity) at toe-off. This condition was validated through a computer simulation of a 7-link musculoskeletal model and measurement experiments of human movements involving stepping and walking. The results of the model simulation were in good agreement with some of the results predicted by the inverted pendulum model. The measurement experiments of walking and stepping movements showed that most COM states at toe-off satisfied the condition for forward progression and the measured trajectories during single support phase were similar to the ballistic trajectories although humans are capable of walking in non-ballistic ways. These results suggested that the necessary condition for forward progression can predict the COM states at toe-off for efficient movement and for avoiding backward falling during single support phase.     

The influences of tropical climate on imagined walking time

This study investigated the effects of a Tropical Climate (TC) on actual and imagined walking times. Participants had to execute and imagine walking 3 distances with or without a 10-kg weight in either a TC or an Air Conditioning (AC) condition. The motor imagery quality was evaluated by computing the isochrony index. The results revealed that movement times were shorter for imagined walking than for actual walking and increased with the distance of the paths in both cases. By contrast, the effect of the load increased actual walking times for the 10- and 15-meter distances without affecting imagined walking times. Importantly, the isochrony index was negatively affected by the increase in load and distance and the effects of distance were amplified in a TC. These findings showed that the environmental climate in which motor imagery arises can modulate the subject’s ability to build up the temporal characteristics of simulated actions.