The use of peripheral vision to guide perturbation-evoked reach-to-grasp balance-recovery reactions

Abstract

For a reach-to-grasp reaction to prevent a fall, it must be executed very rapidly, but with sufficient accuracy to achieve a functional grip. Recent findings suggest that the CNS may avoid potential time delays associated with saccade-guided arm movements by instead relying on peripheral vision (PV). However, studies of volitional arm movements have shown that reaching is slower and/or less accurate when guided by PV, rather than central vision (CV). The present study investigated how the CNS resolves speed-accuracy trade-offs when forced to use PV to guide perturbation-evoked reach-to-grasp balance-recovery reactions. These reactions were evoked, in 12 healthy young adults, via sudden unpredictable anteroposterior platform translation (barriers deterred stepping reactions). In PV trials, subjects were required to look straight-ahead at a visual target while a small cylindrical handhold (length 25%> hand-width) moved intermittently and unpredictably along a transverse axis before stopping at a visual angle of 20°, 30°, or 40°. The perturbation was then delivered after a random delay. In CV trials, subjects fixated on the handhold throughout the trial. A concurrent visuo-cognitive task was performed in 50% of PV trials but had little impact on reach-to-grasp timing or accuracy. Forced reliance on PV did not significantly affect response initiation times, but did lead to longer movement times, longer timeafter-peak-velocity and less direct trajectories (compared to CV trials) at the larger visual angles. Despite these effects, forced reliance on PV did not compromise ability to achieve a functional grasp and recover equilibrium, for the moderately large perturbations and healthy young adults tested in this initial study.

Priming of grasping muscles when viewing a safety handle is diminished with age

“…Support handles can also help us regain stability following an unexpected loss of balance. Several studies have shown that compensatory reach-to-grasp reactions play a significant role when recovering from postural perturbation [25][26][27][28][29]. The fact that the cerebral cortex generates the early hand reaction to quickly grasp a supportive handle [27,26] suggests that in the same way that visual priming shapes voluntary grasping behavior, this mechanism may likewise bias balance recovery actions suited to our surroundings.…”

Motor affordance for grasping a safety handle

“…The aim of the current study was to determine if viewing a safety handle within graspable range could evoke motor output relevant for grasping the handle. Past studies have demonstrated an important role for compensatory reach-to-grasp reactions to establish a new support base using a stable handle following postural perturbation [31][32][33][34][35]. These reactions quickly target the hand to a nearby handle even when vision is occluded at the moment of perturbation, revealing that online visual guidance is not compulsory [31].…”

Do Aging and Dual-Tasking Impair the Capacity to Store and Retrieve Visuospatial Information Needed to Guide Perturbation-Evoked Reach-To-Grasp Reactions?

“…As we noted in the previous study involving only the young adults [8], we are aware of only one previous study showing that a concurrent cognitive task affects the timing of perturbation-evoked reach-to-grasp reactions [36]. In contrast, other previous studies have found that the cognitive task had relatively little effect on the features of the balance-recovery reactions, whether these reactions involved "feet-in-place" responses [37-40], compensatory stepping [37,41-43], or compensatory reach-to-grasp [44]. In the present study, the cognitive tasks were restricted to the recall-delay interval so as to interfere primarily with accurate retention of the handhold location in spatial working memory; however, it seems unlikely that the spatial task would affect memory retention to a similar degree as the non-spatial task [45].…”