Cursus Doelgericht Handelen (BPSN33) R.H. Cuijpers, J.B.J. Smeets and E. Brenner (2004). On the relation between object shape and grasping kinematics. J Neurophysiol, 91: 2598- 2606. R.H. Cuijpers, E. Brenner and J.B.J. Smeets (2006). Grasping reveals visual misjudgements of shape. Exp Brain Res 175:32-44
Curs us Doelgericht Handelen (BPSN33). R.H. Cuijpers, J.B.J. Smeets a nd E. Brenner (2004). On the relation between object shape and grasping kinematics. J Neurophysiol , 91: 2598-2606. - PowerPoint PPT Presentation
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Cursus Doelgericht Handelen(BPSN33)
R.H. Cuijpers, J.B.J. Smeets and E. Brenner (2004). On the relation between object shape and grasping kinematics. J Neurophysiol, 91: 2598-
2606. R.H. Cuijpers, E. Brenner and J.B.J. Smeets (2006). Grasping reveals visual misjudgements of shape. Exp Brain Res 175:32-44
Topics• 1st hour: Control Variables in Grasping
– Opposing views on visuomotor control– Research question
• 2nd hour: Grasping elliptical cylinders– Real cylinders
– If time permits: Modeling grip planning– Conclusions
Control variables in grasping
Many levels of description:• Activity motor neurons• Muscle activity (EMG)• Posture (Joint angles)• Kinetics (Forces, torques)• Kinematics (Position, speed
etc.)• Task level
Degrees of Freedom
(DoF)
low
high
Control variables in grasping
How does the brain ‘plan’/compute the desired motor neuron output?
• If movements are planned in task space:– little computational power needed for planning stage
• But …– Need to solve DoF-problem (Motor primitives)– Cannot control everything (Stereotypic movements)– Need low-level on-line control (e.g. stiffness control)
Control variables in grasping• What is/are the correct level(s) of description for
movement planning and visuomotor control?
Method of research in visuomotor control:• Manipulate visual information / haptic feedback /
proprioceptive feedback• Measure effect on motor output
• Variables that have an effect are ‘controlled’• Variables that have no effect are redundant
Haptic = by touch Proprioceptor = sensory receptor in muscles, tendons or joints
Opposing views on visuomotor control
Fingertip positions and object size• Milner & Goodale: perception vs. action• Franz et al: common source model• Smeets & Brenner: position vs. size
Fingertip positions and object orientation• Glover & Dixon: planning vs. on-line control• Smeets & Brenner: position vs. orientation
perception vs. action
Goodale (1993); Milner, Goodale (1993)
• RV: lesions in occipito-parietal cortex (dorsal).
• DF: damage in ventrolateral occipital areas due to CO poisoning.
Grasping DiscriminationRV DF
Occipito-Parietal
Ventrolateral oocipital
perception vs. action
• Dorsal pathway for guiding movements (should be veridical)
• Ventral pathway for perception (perception of shape, colour etc.)
Dorsal = Action
Ventral = Perception
perception vs. action
Agliotti, De Souza, Goodale (1995):
• Grip aperture NOT influenced by size-illusion.
• Due to separate processing of information for perception and action.
Common source model
• Franz et al (2000): equal effects of illusion
Position vs. size
Brenner, Smeets (1996):• Size-illusion does not affect grip aperture, but does affect
the initial lifting force.• Explanation: not size information is used but position
information. They are inconsistent.
Planning vs. on-line control
Glover & Dixon (2001)
• Relative effect of illusion decreases with time
Illusion mainly affects planning
Position vs. orientation
Smeets et al. (2002)• Assumption:
illusion affects orientation, not position
• Also explains data of Glover and Dixon
Research Question: How is shape information used for
grasping?
• The visually perceived shape is deformed• Shape (ventral) determines where it is best
to grasp an object (dorsal)– Grip locations not veridical
• Shape information could be used during planning (ventral) or on-line control (dorsal)– Grip errors arise early or late in the movement
Grasping elliptical cylinders:real cylinders
Experimental design
• seven 10cm tall cylinders• elliptical circumference with fixed 5cm axis• variable axis: 2, 3, 4, 5, 6, 7 and 8 cm
Experimental Design
Experimental design• Optotrak recorded traces of fingertips• 2 distances x 7 shapes x 6 orientations = 84 trials• 3 repetitions• 10 subjects
Experimental Design
Example
Which positions?• Geometry: grasping is stable at principle axes
Which positions?• Principle axes preferred. But systematic errors…
Which positions?• Systematic "errors" depending on orientation.
• Scaling grip orientation 0.7 except for aspect ratios close to 1, 0.5