Methods Task: Hearing a beep, handle lifting an object vertically to a height of 4 cm, holding it for 3 seconds and replacing it at the second beep. Procedure: 1. Question 1: “Which of two boxes do you expect to be heavier?” (Before lifting any boxes) 2. Exercise Trial 1-8: Exercise trials of lifting medium box. 3. Test Trial 1-16: Test trials of lifting small and big box in alternation. 4. Question 2: “Which of these boxes felt heavier when lifting them?” (After the 5 th and the 16 nd test trials for each box). Results Peak Grip Force: Perception: Question 1: Before any lifting attempt, F.S. and controls expected the big box to be heavier. Question 2: All control subjects experienced the size-weight illusion. F.S. did not show such a consistent illusionary effect: = > After the ipsi-lesional hand lifting, he judged the big object instead of the small object to be heavier. = > After the contra-lesional hand lifting, he judged the small object to be heaviest according to the size-weight illusion. Lost illusion: A left parietal lesion impairs the influence of object size on weight judgement and anticipatory grip force scaling Yong Li 1 , Jennifer Randerath 1 , Georg Goldenberg 2 & Joachim Hermsdörfer 1 1. Clinical Neuropsychology Research Group (EKN), Neuropsychology Clinic, Hospital Munich-Bogenhausen 2. Neuropsychology Clinic, Hospital Munich-Bogenhausen Email: Yong.Li@extern.lrz-muenchen.de Background ! The grip force to grasp and lift an object is based on its intrinsic (i.e., weight) and extrinsic (i.e., size) characteristics (Johansson 1996). ! Size-weight illusion: When lifting two objects with equal weight but different size, we judge the smaller object to be heavier (Charpentier 1891). ! Both sensory based information integration theory and cognitive based high level cognitive/perceptual processes are believed to induce size-weight illusion. ! Perceptual prediction may influence sensorimotor prediction in anticipatory grip force scaling during first few attempts, but this effect disappeared after repetitive lifting, thus it suggests a separation of sensorimotor and cognitive predictions of object weight (Flanagan & Belzner, 2000). ! Posterior parietal cortex (PPC) plays a fundamental role in visuomotor transformations and higher order aspects of motor control. Research Questions: ! Whether the anticipatory scaling of the grip forces according to object properties critically depends on the integrity of the PPC? ! How a deficit in left hemisphere may affect the perceptual size-weight illusion? Discussion ! Abolishing feed forward mode in anticipatory grip force scaling during both hands lifting suggests the critic involvement of patient’s damaged left brain area in sensorimotor planning. " The patient’s intact ability to employ a safety margin to secure lift-off then successfully update this erroneous forward model for the single novel stimulus suggests that patient’s lesion area may be involved in integrating the size discrepancy between two objects into sensorimotor prediction. ! ! The non-impaired size-weight illusion perception of F.S. after contra-lesional hand lifting could be that patient’s intact comparison region in the right inferior parietal cortex (supramarginal gyrus) obtained the actual weight information of big and small boxes, then feed it to the perceptual decision making process which integrates perceptual prediction (expected weight from size) and sensorimotor feedback (perceived actual weight) (Jenmalm et al 2006). ! ! The impaired size-weight illusion perception of F.S. after ipsi-lesional hand lifting may be the lesion related inability to integrate actual sensorimotor feedback into the process of size-weight illusion (Jenmalm et al 2006). Conclusion Our findings suggest that left temporal parietal cortex may play an important role in planning actions of both hands and integrating sensorimotor feedback (actual weight) comparison of ipsi-lesional hand into the process of size-weight illusion perception. Reference 1. Charpentier, A. (1891). Analyse experimentale quelques elements de la sensation de poids [Experimental study of some aspects of weight perception]. Archives de Physiologie Normales et Pathplogiques, 3 , 122-135. 2. Flanagan J.R. & Beltzner M.A. (2000). Independence of perceptual and sensorimotor predictions in the size-weight illusion. Nature Neuroscience , 3 , 737-741. 3. Johansson, R.S., (1996). Sensory control of dexterous manipulation in humans. In: Wing, A.M., Haggard, P., Flanagan, J.R. (Eds.), Hand and Brain . Academic Press, San Diego, pp. 381–414. 4. Jenmalm P, Schmitz C, Forssberg H, Ehrsson HH. (2006). Lighter or heavier than predicted: neural correlates of corrective mechanisms during erroneously programmed lifts. Journal of Neuroscience , 26(35), 9015-21. MRT-Scan of F.S. left left right right Subjects: ! F.S.: male, 56 year old, right-handed, who suffered large lesion in the left parietal and temporal lobe due to intra- cerebral bleeding (see MRT-Scan). F.S. showed severe apraxia, moderate aphasia, but preserved gross contra- lateral motor function. ! Control: 5 male healthy persons, 55±5.2 years old, right- handed. Setup & Apparatus: In contrast to the controls, F.S. did not scale his grip forces according to his weight expectations when lifting the small and big box in the first few attempts ( squared area ) by both hands. Note: The peak grip force rate data confirm the tendency of peak grip force. medium: 9.8 cm small: 6.2 cm large: 15.8 cm platform F.S. Left Hand 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 1 3 5 7 2 4 6 8 10 12 14 16 Big Small Medium Execise Trials Test Trials GFMax (N) F.S. Right Hand 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 1 3 5 7 2 4 6 8 10 12 14 16 Big Small Medium Execise Trials Test Trials GFMax (N) Control B Left Hand 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 1 3 5 7 2 4 6 8 10 12 14 16 Big Small Medium Execise Trials Test Trials GFMax (N) Control K Right Hand 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 1 3 5 7 2 4 6 8 10 12 14 16 Big Small Medium Execise Trials Test Trials GFMax (N) Control S Right Hand 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 1 3 5 7 2 4 6 8 10 12 14 16 Big Small Medium Execise Trials Test Trials GFMax (N) Control V Right Hand 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 1 3 5 7 2 4 6 8 10 12 14 16 Big Small Medium Execise Trials Test Trials GFMax (N) Box weight: 320g GF GF sensor 17th Annual Meeting of Neural Control of Movement, March 25-30, 2007 Seville, Spain Control MV Left Hand 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 1 3 5 7 2 4 6 8 10 12 14 16 Big Small Medium Execise Trials Test Trials GFMax (N)