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Acquiring and adapting a novel audiomotor map in human grasping.
Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
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.

Place, publisher, year, edition, pages
2006. Vol. 173, no 3, 487-497 p.
Keyword [en]
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: urn:nbn:se:umu:diva-12657DOI: doi:10.1007/s00221-006-0394-xPubMedID: 16506001OAI: oai:DiVA.org:umu-12657DiVA: diva2:152328
Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Sensorimotor transformations during grasping movements
Open this publication in new window or tab >>Sensorimotor transformations during grasping movements
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
sensorimotor transformation, sensory integration, visuomotor map, human physiology, adaptation, grasping, sensory substitution
National Category
Physiology
Identifiers
urn:nbn:se:umu:diva-781 (URN)91-7264-077-4 (ISBN)
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

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Publisher's full textPubMedhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Retrieve&list_uids=16506001&dopt=Citation

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