This study was designed to determine if movement planning strategies incorporating the use of visual feedback during manual aiming are specific to individual movements. Advance information about target location and visual context was manipulated using precues. Participants exhibited a shorter reaction time and a longer movement time when they were certain of the target location and that vision would be available. The longer movement time was associated with greater time after peak velocity. Under conditions of uncertainty, participants prepared for the worst-case scenario. That is, they spent more time organizing their movements and produced trajectories that would be expected from greater open-loop control. Our results are consistent with hierarchical movement planning in which knowledge of the movement goal is an essential ingredient of visual feedback utilization.
"Signals from the FSRs switched smart-glass goggles (see ) from transparent to translucent (occluding the lvf) at either heel contact of penultimate (right) or final (left) step before the obstacle, and back to transparent at right foot contact following crossing (Fig. 1). Lvf occlusion trials were presented with a 1:4 ratio, which avoided participants planning for 'worst case scenario'  and increasing weighting of central visual cues/feedforward mechanisms . Trials were repeated three times (each height) giving 12 perturbed and 48 unperturbed. "
[Show abstract][Hide abstract] ABSTRACT: Although gaze during adaptive gait involving obstacle crossing is typically directed two or more steps ahead, visual information of the swinging lower-limb and its relative position in the environment (termed visual exproprioception) is available in the lower visual field (lvf). This study determined exactly when lvf exproprioceptive information is utilised to control/update lead-limb swing trajectory during obstacle negotiation. 12 young participants negotiated an obstacle wearing smart-glass goggles which unpredictably occluded the lvf for certain periods during obstacle approach and crossing. Trials were also completed with lvf occluded for the entirety of the trial. When lvf was occluded throughout, foot-placement distance and toe-clearance became significantly increased; which is consistent with previous work that likewise used continuous lvf occlusion. Both variables were similarly affected by lvf occlusion from instant of penultimate-step contact, but both were unaffected when lvf was occluded from instant of final-step contact. These findings suggest that lvf (exproprioceptive) input is typically used in an online manner to control/update final foot-placement, and that without such control, uncertainty regarding foot placement causes toe-clearance to be increased. Also that lvf input is not normally exploited in an online manner to update toe-clearance during crossing: which is contrary to what previous research has suggested.
"However, no change in the timing of the grasp was predicted as this has previously be shown to be robust against visual occlusion (Mazyn et al. 2007b). In the absence of explicit advance knowledge, it was hypothesised that participants would respond initially with a default control strategy irrespective of the presence and duration of visual occlusion (Jakobson and Goodale 1991; Khan et al. 2002; Hansen et al. 2006; Mazyn et al. 2007b). "
[Show abstract][Hide abstract] ABSTRACT: This study examined how explicit advance knowledge might influence adaptive behavior to visual occlusions. Catching performance and kinematics of good ball catchers were compared between no, early and late occlusion trials. Discrete visual occlusions of 400 ms, occurring early or late in the ball's approach trajectory, were randomly interspersed between no occlusion trials. In one condition, the presence and type of occlusion were announced a priori (expected), whereas in another condition no such information was provided (unexpected). Expectation of occlusion resulted in an adapted limb transport and increased grasping time, whereas in the unexpected condition a higher peak of wrist velocity was evident for all occlusion conditions. The observed different adaptations cannot be explained by trial-by-trial adaptations alone and instead provide evidence for the influence of explicit advance knowledge in the motor response of interceptive actions.
Experimental Brain Research 08/2011; 214(4):483-90. DOI:10.1007/s00221-011-2846-1 · 2.04 Impact Factor
"This is exactly what we observed in Experiment 2 of the present study with the acceleration and deceleration phases of the movement accounting for 53 and 47% of movement time, respectively. When visual feedback is available, it has been proposed that a strategy allowing participants to perform online corrections would be preferred (Elliott and Allard 1985; Elliott and Calvert 1990; Elliott et al. 1991; Hansen et al. 2006; Mackrous and Proteau 2007). For example, Mackrous and Proteau (2007) observed that participants spent approximately 60% of movement time in the deceleration phase of the movement, leaving more time to adjust/modulate the movement when it closed on the target. "
[Show abstract][Hide abstract] ABSTRACT: A modulation of the primary impulse of manual/video-aiming movements performed without visual feedback has been reported. In the present study, we show that this modulation is modified (a) with increased practice, (b) the use of an aligned visual display, and (c) the availability of visual feedback on alternated trials. However, this modulation was not as efficient as that observed in a normal vision condition, which underlines the primary role of vision to ensure endpoint accuracy. Moreover, this modulation was observed only on the extent component of the task. This last observation indicates that proprioception can be used to modulate the extent component of goal-directed movements but that vision is necessary to modulate their direction.
Psychological Research 04/2009; 74(2):182-95. DOI:10.1007/s00426-009-0229-z · 2.47 Impact Factor
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