Grasping trapezoidal objects

Kleinholdermann, Urs; Brenner, Eli; Franz, Volker H.; Smeets, Jeroen B. J.

doi:10.1007/s00221-007-0867-6

Cited by 27 publications

(25 citation statements)

References 14 publications

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“…4 of [75]. The observed angles are more similar to the angles predicted by our model (red lines) than to the angles predicted by the model of Smeets and Brenner (blue lines) or to simple grip closure (grey open circles).…”

Section: Resultssupporting

confidence: 72%

Grasping Kinematics from the Perspective of the Individual Digits: A Modelling Study

Verheij¹,

Brenner²,

Smeets³

2012

PLoS ONE

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Grasping is a prototype of human motor coordination. Nevertheless, it is not known what determines the typical movement patterns of grasping. One way to approach this issue is by building models. We developed a model based on the movements of the individual digits. In our model the following objectives were taken into account for each digit: move smoothly to the preselected goal position on the object without hitting other surfaces, arrive at about the same time as the other digit and never move too far from the other digit. These objectives were implemented by regarding the tips of the digits as point masses with a spring between them, each attracted to its goal position and repelled from objects' surfaces. Their movements were damped. Using a single set of parameters, our model can reproduce a wider variety of experimental findings than any previous model of grasping. Apart from reproducing known effects (even the angles under which digits approach trapezoidal objects' surfaces, which no other model can explain), our model predicted that the increase in maximum grip aperture with object size should be greater for blocks than for cylinders. A survey of the literature shows that this is indeed how humans behave. The model can also adequately predict how single digit pointing movements are made. This supports the idea that grasping kinematics follow from the movements of the individual digits.

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Section: Resultssupporting

confidence: 72%

Grasping Kinematics from the Perspective of the Individual Digits: A Modelling Study

Verheij¹,

Brenner²,

Smeets³

2012

PLoS ONE

Self Cite

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show abstract

“…When grasping the former, symmetrical, target (i.e., most analogous to the cylinders in our experiments) it was the thumb landing-site to which gaze was principally directed; the finger-side of the shapes only attracted substantial fixations on the task in which this digit had to be guided to the apex of the triangle, the site which was most difficult to contact. While it is clear that further studies of fixation strategies associated with different grasping actions and orientations are warranted, including those involving complex/asymmetric objects (Lederman and Wing 2003;Kleinholdermann et al 2007), for the moment, self-observation testifies to the validity of the results presented here.…”

Section: Discussionsupporting

confidence: 52%

Getting a grip: different actions and visual guidance of the thumb and finger in precision grasping

Melmoth

Grant

2012

Exp Brain Res

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This is the unspecified version of the paper.This version of the publication may differ from the final published version. Permanent repository link AbstractWe manipulated the visual information available for grasping to examine what is visually guided when subjects get a precision grip on a common class of object (upright cylinders). In Experiment 1, objects (2 sizes) were placed at different eccentricities to vary the relative proximity to the participant's (n=6) body of their thumb and finger contact positions in the final grip orientations, with vision available throughout or only for movement programming.Thumb trajectories were straighter and less variable than finger paths, and the thumb normally made initial contact with the objects at a relatively invariant landing site, but consistent thumbfirst contacts were disrupted without visual guidance. Finger deviations were more affected by the object's properties and increased when vision was unavailable after movement onset. In Experiment 2, participants (n=12) grasped 'glow-in-the-dark' objects wearing different luminous gloves in which the whole hand was visible or the thumb or the index finger were selectively occluded. Grip closure times were prolonged and thumb-first contacts disrupted when subjects could not see their thumb, whereas occluding the finger resulted in wider grips at contact because this digit remained distant from the object. Results were together consistent with visual feedback guiding the thumb in the period just prior to contacting the object, with the finger more involved in opening the grip and avoiding collision with the opposite contact surface. As people can overtly fixate only one object contact-point at a time, we suggest that selecting one digit for on-line guidance represents an optimal strategy for initial grip placement.

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“…As the movements of the digits when reaching to grasp an object are constrained to have a more or less perpendicular approach to the surface to apply forces in opposite directions with the two digits when grasping (Biegstraaten et al 2006;Kleinholdermann et al 2007;Smeets and Brenner 1999), tasks that involve reaching to touch or to push an object can be designed to impose similar constraints on each digit to those during grasping. Such tasks can be used to test the second prediction .…”

Section: Time Course Of Grip-aperture Formationmentioning

confidence: 99%

“…To test whether people aim for a perpendicular approach, one should grasp objects for which closing one's grip does not lead to movements that approach the surface perpendicularly, such as trapezoids. Experiments with such objects showed that the digits' trajectories when closing the grip tend to approach the surface perpendicularly (Kleinholdermann et al 2007). Thus the digits were moving along suitable paths for the orientation of the surfaces that they were heading for, rather than just moving toward each other.…”

Section: Time Course Of Grip-aperture Formationmentioning

confidence: 99%