Invariance and optimality in motor production and perception


October 13, 2014 - 1:00pm
NW 243
About the Speaker
Yaron Meirovitch (Weizmann Institute of Science)

The ability of the nervous system to generate reliable complicated motion patterns in spite of the redundant mappings between motor commands and motor output is not fully understood. Specifically, ample research addressed the selection of specific paths and the preference toward specific kinematic profiles. The CNS was suggested to employ movement principles based on relatively few building blocks (movement primitives) that may constrain the redundancy from joint to task space while manifesting a stereotypical movement behavior at the end-effector level. Non-Euclidean geometries were previously used to account for two such movement principles: the 2/3 power law which is equivalent to moving at a constant equi-affine speed (Flash and Handzel, 2007) and the isochrony principle (implying constant full-affine speed).

Three studies based on these lines of research will be presented.

The first study suggests that movement regularities in the form of curvature-speed power laws succinctly encode natural complex wrist trajectories recorded from Israeli Sign Language movements. This encoding shows that the complex motor output is regularized by long individual segments that are governed by different kinematic rules.

The second study presents geometric building blocks for movement generation which are based on full-affine orbits. Specifically, the affine orbits will be shown to associate movement optimality with invariance.  An invariant segmentation based on affine orbits will then be used to represent complex movements. Finally, hand speed profiles can be accurately predicted using only the geometrical path of the hand’s trajectory based on the mixture of geometries model and the constrained minimum jerk.   

The third study shows evidence from EEG that the observation of 2/3 power law visual motions attenuates the cortical alpha and beta rhythms, known as Event Related Desynchronization ERD. Together with other previous studies (Dayan et al., 2007), this will be used to claim that kinematic regularities as the 2/3 power law are centrally represented. These findings indicate that the widely studied mu suppression and the alpha and beta ERD phenomena can be evoked by observation of abstract motions where the power attenuations are temporally and topographically selective to the type of regularities governing the kinematics.  

Finally, the results from these studies will be discussed in the framework of movement primitives. The requirement for both further theoretical accounts and neural evidence for these representations will be emphasized.