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Sensorimotor transformations during grasping movements
Umeå University, Faculty of Medicine, Integrative Medical Biology.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

‘Sensorimotor transformations’ are processes whereby sensory information is used to generate motor commands. One example is the ‘visuomotor map’ that transforms visual information about objects to motor commands that activates various muscles during grasping movements. In the first study we quantified the relative impact (or ‘weighting’) of visual and haptic information on the sensorimotor transformation and investigated the principles that regulates the weighting process. To do this, we let subjects perform a task in which the object seen (visual object) and the object grasped (haptic object) were physically never the same. When the haptic object became larger or smaller than the visual object, subjects in the following trials automatically adapted their maximum grip aperture (MGA) when reaching for the object. The adaptation process was quicker and relied more on haptic information when the haptic objects increased in size than when they decreased in size. As such, sensory weighting is molded to avoid prehension error.

In the second study we investigated the degree to which the visuomotor map could be modified. Normally, the relationship between the visual size of the object (VO) and the MGA can be expressed as a linear relationship, where MGA = a + b * VO. Our results demonstrate that subjects inter- and extrapolate in the visuomotor map (that is, they are reluctant to abandon the linear relationship) and that the offset (a) but not the slope (b) can be modified.

In the third study, we investigated how a ‘new’ sensorimotor transformation can be established and modified. We therefore replaced the normal input of visual information about object size with auditory information, where the size of the object was log-linearly related to the frequency of a tone. Learning of an audiomotor map consisted of three distinct phases: during the first stage (~10-15 trials) there were no overt signs of learning. During the second stage there was a period of fast learning where the MGA became scaled to the size of the object until the third stage where the slope was constant.

The purpose of the fourth study was to investigate the sensory basis for the aperture adaptation process. To do that, the forces acting between the fingertips and the object was measured as the subjects adapted. Our results indicate that information about when the fingers contacts the object, that is, the ‘timing’ of contact, is likely to be used by the CNS to encode an unexpected object size.

Since injuries and disease can affect the sensorimotor transformations that controls the hand, knowledge about how these processes are established and modified may be used to develop techniques for sensory substitution and other rehabilitation strategies.

Place, publisher, year, edition, pages
Umeå: Integrativ medicinsk biologi , 2006. , 51 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1028
Keyword [en]
sensorimotor transformation, sensory integration, visuomotor map, human physiology, adaptation, grasping, sensory substitution
National Category
Physiology
Identifiers
URN: urn:nbn:se:umu:diva-781ISBN: 91-7264-077-4 (print)OAI: oai:DiVA.org:umu-781DiVA: diva2:144510
Public defence
2006-05-23, BiA201, Biologihuset flygel A, Umeå universitet, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2006-05-02 Created: 2006-05-02 Last updated: 2009-10-29Bibliographically approved
List of papers
1. Task requirements influence sensory integration during grasping in humans.
Open this publication in new window or tab >>Task requirements influence sensory integration during grasping in humans.
2004 (English)In: Learning & memory (Cold Spring Harbor, N.Y.), ISSN 1072-0502, Vol. 11, no 3, 356-363 p.Article in journal (Refereed) Published
Abstract [en]

The sensorimotor transformations necessary for generating appropriate motor commands depend on both current and previously acquired sensory information. To investigate the relative impact (or weighting) of visual and haptic information about object size during grasping movements, we let normal subjects perform a task in which, unbeknownst to the subjects, the object seen (visual object) and the object grasped (haptic object) were never the same physically. When the haptic object abruptly became larger or smaller than the visual object, subjects in the following trials automatically adapted their maximum grip aperture when reaching for the object. This adaptation was not dependent on conscious processes. We analyzed how visual and haptic information were weighted during the course of sensorimotor adaptation. The adaptation process was quicker and relied more on haptic information when the haptic objects increased in size than when they decreased in size. As such, sensory weighting seemed to be molded to avoid prehension error. We conclude from these results that the impact of a specific source of sensory information on the sensorimotor transformation is regulated to satisfy task requirements.

Keyword
Adult, Biomechanics, Female, Hand/*physiology, Hand Strength/*physiology, Humans, Male, Movement/*physiology, Perception/*physiology, Photic Stimulation, Psychomotor Performance/*physiology, Reaction Time, Reference Values
Identifiers
urn:nbn:se:umu:diva-12655 (URN)doi:10.1101/lm.71804 (DOI)15169866 (PubMedID)
Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2010-06-24Bibliographically approved
2. Short-term plasticity of the visuomotor map during grasping movements in humans.
Open this publication in new window or tab >>Short-term plasticity of the visuomotor map during grasping movements in humans.
2005 (English)In: Learning & memory (Cold Spring Harbor, N.Y.), ISSN 1072-0502, Vol. 12, no 1, 67-74 p.Article in journal (Refereed) Published
Abstract [en]

During visually guided grasping movements, visual information is transformed into motor commands. This transformation is known as the "visuomotor map." To investigate limitations in the short-term plasticity of the visuomotor map in normal humans, we studied the maximum grip aperture (MGA) during the reaching phase while subjects grasped objects of various sizes. The objects seen and the objects grasped were physically never the same. When a discrepancy had been introduced between the size of the visual and the grasped objects, and the subjects were fully adapted to it, they all readily interpolated and extrapolated the MGA to objects not included in training trials. In contrast, when the subjects were exposed to discrepancies that required a slope change in the visuomotor map, they were unable to adapt adequately. They instead retained a subject-specific slope of the relationship between the visual size and MGA. We conclude from these results that during reaching for grasping, normal subjects are unable to abandon a straight linear function determining the relationship between visual object size and MGA. Moreover, the plasticity of the visuomotor map is, at least in short term, constrained to allow only offset changes, that is, only "rigid shifts" are possible between the visual and motor coordinate systems.

Keyword
Adolescent, Adult, Algorithms, Female, Fingers/innervation/physiology, Hand/innervation/physiology, Hand Strength/*physiology, Humans, Male, Neuronal Plasticity/*physiology, Orientation/physiology, Psychomotor Performance/*physiology, Size Perception, Visual Perception/physiology
Identifiers
urn:nbn:se:umu:diva-12771 (URN)doi:10.1101/lm.83005 (DOI)15687231 (PubMedID)
Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2010-06-24Bibliographically approved
3. Acquiring and adapting a novel audiomotor map in human grasping.
Open this publication in new window or tab >>Acquiring and adapting a novel audiomotor map in human grasping.
2006 (English)In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 173, no 3, 487-497 p.Article in journal (Refereed) Published
Abstract [en]

For sensorimotor transformations to be executed accurately, there must be mechanisms that can both establish and modify mappings between sensory and motor coordinates. Such mechanisms were investigated in normal subjects using a reach-to-grasp task. First, we replaced the normal input of visual information about object size with auditory information, i.e., we attempted to establish an 'audiomotor map'. The size of the object was log linearly related to the frequency of the sound, and we measured the maximum grip aperture (MGA) during the reaching phase to determine if the subjects had learned the relationship. Second, we changed the frequency-object size relationship to study adaptation in the newly acquired map. Our results demonstrate that learning of an audiomotor map consisted of three distinct phases: during the first stage (approximately 10-15 trials) subjects simply used MGAs large enough to grasp any reasonably sized object and there were no overt signs of learning. During the second stage, there was a period of fast learning where the slope of the relationship between MGA and object size became steeper until the third stage where the slope was constant. In contrast, when sensorimotor adaptation was studied in the established audiomotor map, there was rapid learning from the start of a size perturbation. We conclude that different learning strategies are employed when sensorimotor transformations are established compared to when existing transformations are modified.

Keyword
Acoustic Stimulation, Adaptation; Physiological/physiology, Adult, Algorithms, Brain Mapping, Data Interpretation; Statistical, Female, Functional Laterality/physiology, Hand/innervation/physiology, Hand Strength/*physiology, Humans, Male, Movement/physiology, Photic Stimulation, Psychomotor Performance/physiology, Size Perception/physiology, Space Perception/*physiology
Identifiers
urn:nbn:se:umu:diva-12657 (URN)doi:10.1007/s00221-006-0394-x (DOI)16506001 (PubMedID)
Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2010-06-24Bibliographically approved
4. The sensory basis for aperture adaptation during grasping movements
Open this publication in new window or tab >>The sensory basis for aperture adaptation during grasping movements
(English)Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-5119 (URN)
Available from: 2006-05-02 Created: 2006-05-02 Last updated: 2010-06-24Bibliographically approved

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