Kamp, Cornelis van de

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Proceedings - University of Groningen

   University of GroningenGetting a grip on graspingKamp, Cornelis van deIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2011Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Kamp, C. V. D. (2011). Getting a grip on grasping. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 03-06-2022suMMarySUMMARY124GettinG a Grip on GraspinG Grasping enables humans to get a grip on a variety of  surrounding things. This thesis describes a number of  experiments studying grasping behavior. The aim of  this thesis is to get a better understanding of  how grasping movements are controlled in catching and prehension movements.Chapter 1, is meant to provide some background on the experimental work reported in this thesis. The framework for the studies presented in this thesis is provided by a vast body of  research on the visual guidance of  goal-directed movements like hitting, catching, and prehension. A major research question that has been referred to in these studies concerned the timing of  these movements. For instance, how do we, before raising our glass, manage to close our grasping hand around it in just the right time and place? In order to answer this question, this thesis focused on 1) the controlled variables, 2)the information, and  3) the control law. Previous studies paved the way in the development of  these fundamental underpinnings of  motor control. Zaal and colleagues (e.g. Zaal & Bootsma, 2004; Zaal, Bootsma, & Van Wieringen, 1998), for example, provided a model that based on time-to-contact information (tau) predicts the moment of  hand closure in prehension. This ‘dynamic-tau model’, central to this thesis, combines elements of  the theories of  direct-perception and dynamical systems.Before focusing on the information and the control law involved in grasping, the question: ‘what are the controlled variables in prehension?’ is addressed in Chapter 2. After 20 years of  prehension research that had been based mainly on Jeannerod’s (1981, 1984) hypothesis that prehension should be considered as the coordinated act of  a reaching and a grasping movement, Smeets & Brenner (1999) proposed ‘a new view on grasping’. Their alternative explanation was that prehension might just as well be seen as the simultaneous pointing movements of  the thumb and the index finger. Whereas, traditionally, the hand aperture (i.e. the distance between thumb and index finger) had always been considered to be one of  the controlled variables in grasping, according to Smeets and Brenner’s ‘double pointing hypothesis’, this hand aperture is really an emergent property related to the time course of  the positions of  the two digits moving to their respective end points. In Chapter 2 the latter hypothesis SUMMARY125was tested by perturbing the end position of  one of  the digits while leaving the end position of  the opposing digit unchanged. In the experiment reported in Chapter 2 participants reached for and grasped an object of  which the side surfaces could be made to slide in and out just after the reaching movement had started. In conflict with Smeets and Brenner’s double-pointing hypothesis, it was found that in some cases, perturbing the end position of  one digit also affected the kinematics of  the opposing digit. This finding clearly disagrees with the double-pointing account.  Therefore, it was concluded that rejecting the latter hypothesis logically leads to accepting the reaching and grasping hypothesis.With two components making up one act, reaching and grasping, somehow, need to be coordinated. The traditional view on this issue has been that the grasping is temporally ordered on the time scale provided by reaching. Empirical evidence for a hierarchy of  reaching over grasping seemed to come from experiments showing that when object location or size were changed at movement onset, adjustments in the reach component were much faster than adjustments in the grasp component. In Chapter 3 of  this thesis, this account is challenged by the finding that the grasp component can be just as rapid in responding to a change in object size (within 120 ms) as the reach component is reported to respond to a change in object position. These findings imply that the time scale on which an adjustment in the grasp component is ordered is not necessarily provided by reaching. This means that, empirically, the control model of  a hierarchy of  reaching over grasping lost one of  its fundamental underpinnings.This thesis studies an alternative means to consider the way the grasp component might adjust to size perturbations proposing that the responses to such perturbations result from the online control of  the hand aperture. Instead of  being ordered in a predefined hierarchical fashion the kinematic details of  a grasping movement are believed to be continuously regulated, online, based on time-to-contact information. In Chapters 4 and 5, both the control law and the information that might be used for the control of  hand closure initiation in grasping have been addressed. The idea tested in these chapters is that grasping behavior is best understood from an approach combining elements of  the theories of  direct-perception and dynamical systems. In a control scenario SUMMARY126that involves first-order time-to-contact information, it does not really matter whether the hand moves toward the object, the object moves towards the hand or a combination of  both takes place. This is because the first-order time-to contact information is about the relative hand-object movement. Chapters 4 and 5 describe a number of  experiments that provide evidence for a generic model for understanding the control of  hand-closure initiation in both catching and prehension.Chapter 6 reviews the impact of  the results presented in this thesis. In this last chapter the implications, contributions, deficits, and practical application of  the knowledge gained by this thesis are being discussed. 

Getting a grip on grasping

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Getting a grip on grasping

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