Visual dominance in amending the directional parameter of feedforward control

The effects of inaccessible visual feedback used concurrently or terminally

[Purpose] Concurrent feedback is more detrimental for long-term retention of motor skills because learners depend on accessible visual information provided in parallel with movements. However, visual information is not always accessible. Furthermore, the effects of concurrent feedback vary with aspects of the task being performed. We investigated the effects of inaccessible visual feedback used concurrently or terminally, focusing on aspects of movement. [Subjects and Methods] Fourteen subjects were quasi-randomly assigned to either a concurrent feedback group or a terminal feedback group. They practiced a task that involved right shoulder flexion with a specific acceleration. Learning achievements were assessed by measurement of errors in movement duration, peak timing, and strength. [Results] Regarding errors in movement duration, the concurrent feedback group was superior to the terminal feedback group during the midterm and final sessions. Regarding errors in peak timing, learning occurred in the concurrent feedback group, but not in the terminal feedback group because the improvement in performance during practice was inadequate. Regarding errors in peak strength, learning occurred in both groups. [Conclusion] Concurrent visual feedback that is used inaccessibly has learning effects that either equal or surpass those of terminal feedback that is used with inaccessible visual information for all parameters.

Manual and oculomotor performance develop contemporaneously but independently during continuous tracking

The coordination of the oculomotor and manual effector systems is an important component of daily motor behavior. Previous work has primarily examined oculomotor/manual coordination in discrete targeting tasks. Here we extend this work to learning a tracking task that requires continuous response and movement update. Over two sessions, participants practiced controlling a computer mouse with movements of their arm to follow a target moving in a repeated sequence. Eye movements were also recorded. In a retention test, participants demonstrated sequence-specific learning with both effector systems, but differences between effectors also were apparent. Time series analysis and multiple linear regression were employed to probe spatial and temporal contributions to overall tracking accuracy within each effector system. Sequence-specific oculomotor learning occurred only in the spatial domain. By contrast, sequence-specific learning at the arm was evident only in the temporal domain. There was minimal interdependence in error rates for the two effector systems, underscoring their independence during tracking. These findings suggest that the oculomotor and manual systems learn contemporaneously, but performance improvements manifest differently and rely on different elements of motor execution. The results may in part be a function of what the motor learning system values for each effector as a function of its effector's inertial properties.

Influence of vision on head stabilization strategies in older adults during walking

BACKGROUND

Maintaining balance during dynamic activities is essential for preventing falls in older adults. Head stabilization contributes to dynamic balance, especially during the functional task of walking. Head stability and the role of vision in this process have not been studied during walking in older adults.

METHODS

Seventeen older adults (76.2 +/- 6.9 years) and 20 young adults (26.0 +/- 3.4 years) walked with their eyes open (EO), with their eyes closed (EC), and with fixed gaze (FG). Participants performed three trials of each condition. Sagittal plane head and trunk angular velocities in space were obtained using an infrared camera system with passive reflective markers. Frequency analyses of head-on-trunk with respect to trunk gains and phases were examined for head-trunk movement strategies used for head stability. Average walking velocity, cadence, and peak head velocity were calculated for each condition.

RESULTS

Differences between age groups demonstrated that older adults decreased walking velocity in EO (p =.022). FG (p = .021), and EC (p = .022). and decreased cadence during EC (p = .007). Peak head velocity also decreased across conditions (p < .0001) for older adults. Movement patterns demonstrated increased head stability during EO. diminished head stability with EC, and improved head stability with FG as older adult patterns resembled those of young adults.

CONCLUSIONS

Increased stability of the lower extremity outcome measures for older adults was indicated by reductions in walking velocity and cadence. Concomitant increases in head stability were related to visual tasks. Increased stability may serve as a protective mechanism to prevent falls. Further, vision facilitates the head stabilization process for older adults to compensate for age-related decrements in other sensory systems subserving dynamic balance.