Role of Actual (Physical) Ability in Estimating Reach

Purpose

Arguably, estimation of whether an object is reachable or not from a specific body position constitutes an important aspect in effective motor planning. Studies of verbal estimates of reachability suggest that directional bias (over- or underestimation) is based in part on perceived ability and perceived task demands. The aim of this study was to determine the relation between actual physical ability and perceived ability in estimating reach. That is, does actual ability play a significant role in the planning (estimating) of reach movements?

Methods

We explored this notion by comparing adults (N = 30) on estimates of reach while seated (P1) and in a more demanding posture of standing on one foot and leaning forward (P2). Prior to testing, participants were measured for actual balance ability and divided into low and high skill level. Each condition (P1 / P2) involved seven midline target presentations given in random order with five trials at each site; conditions were counterbalanced between participants.

Analysis/Results

The basis for data analysis was the comparison between actual ability, actual reach and estimation of reach using chi-square, ANOVA and relationship analyses. The key expectations were that the ability groups would differ little in the P1 (seated) condition and high ability group would be more accurate in the more demanding P2 condition, due to better movement awareness of ability. In view of the participants overall (not by ability group), although there was no difference between conditions for total error, results for the distribution and direction of error indicated distinctions. As expected, participants overestimated in the P1 condition and underestimated in the P2 condition.

Conclusions

From a confidence perspective, it seems reasonable that while seated and with relatively (and comparatively) minimal postural constraints (P1), participants would feel confident in reachability, resulting in overestimation. In the P2 condition, we expected that with perceived greater postural constraints, participants would have less confidence, therefore using a more conservative strategy resulting in less overestimation. Interestingly, there were no differences between high and low ability group scores and reachability. Relationship analyses indicated no support for the idea that actual physical ability is significantly associated with estimates of reach. These results prompt speculation that estimates of reach are founded more in perceived ability, rather than actual limits of physical ability. In other words, such planning is based to a great extent on psychological factors, such as confidence and motivation.