We investigated a general theory accounting for the guidance of ongoing movements in an interceptive reaching task. The aim was to assess the premise of tau-coupling that the coupling constant k, the ratio of taus (τs) of motion gaps between hand and object, reflects the kinematics of the on-going movement. The spatial and temporal constraints of the interceptive action were manipulated in three task conditions. While the time dependent counterpart of k, K(t) exhibited task effects, k itself could not distinguish between task manipulations. K(t) showed large variability during the initial acceleration phase, small variability during the rest of the movement, and task dependent changes during the final deceleration phase of interception. The findings highlight the importance of clarifying what constitutes as t-coupling.
Joanne Smith, Madeleine Grealy and Gert-Jan Pepping
Gert-Jan Pepping and François-Xavier Li
Studies on affordance perception commonly report systematic errors; a finding that is at odds with the observation that everyday motor behavior is accurate. The present study investigated whether the means by which perceptual performance is measured could explain the reported errors. Perception of overhead reachability and reaction time were measured using a verbal and an actual reaching response in a standing reach, and a reach-and-jump. Results show that participants accurately perceived their action boundaries for both tasks and in both response conditions. A simple reach, however, took less time to initiate (1,094 ms) than a reach-and jump (1,214 ms). Interestingly, the verbal response took considerably more time to initiate (1,424 ms) than the actual reach (1,154 ms). These results suggest that making verbal judgments about affordances is a different task than actually acting on them. It is therefore concluded that the use of conscious judgments to measure perceptual performance should be considered with care.
Steven van Andel, Michael H. Cole and Gert-Jan Pepping
Objectives: To examine gait regulation during the approach to stepping onto a curb for older adults who did or did not report gait-related falls over a 12-month follow-up. Methods: A total of 98 participants aged 60 years and older were analyzed. Primary outcomes were step length adaptations (lengthening or shortening) during a curb approach and the occurrence of a gait-related fall during a 12-month follow-up. Results: Linear mixed-effects modeling indicated stronger adaptations toward the end of the approach. Participants who reported experiencing a gait-related fall showed a stronger relationship between the adjustment required and adjustment produced, indicating different gait adaptations during the step leading onto the curb. Discussion: The link between prospective gait-related falls and gait adaptations indicated that older adults with reduced capabilities require stronger adaptations to complete tasks reminiscent of everyday life. This finding may provide insight into the mechanisms of falls in older adults and should inform new fall prevention interventions.