Perhaps the problem with focusing on the human prehension is that our "reach exceeds our grasp." And yet there are many insights we can draw from nature in this, as in other endeavors. Human prehension is incredibly complex. We should be cautious about drawing conclusions regarding the best morphology, sensing, learning or control when dealing with a phenomenon that consumes a substantial fraction of the human motor cortex and requires more than 10 years for humans to master with adult proficiency.

If we set out sights a bit lower, we obtain useful insights about grasping and manipulation from animals such as frogs, lizards and birds. (We can also learn from the primitive grasping and exploration responses of very young infants [Twitchell65].)

There is less literature on strategies approaches for object acquisition and stabilization in primitive animals than there is for locomotion. Still, some interesting insights result from the strategies of aurans (e.g. [Comer81; Gray97; ]) birds, arthropods and other animals. The approach of animals like frogs to acquiring and manipulating objects (e.g. capturing prey and bringing it to the mouth) seems inelegant (for example see video clip at http://bdml.stanford.edu/twiki/bin/view/Main/FrogManipulation) but is effective, and robust with respect to disturbances.

In contrast to grasp planning in robotics (including preparatory actions), which seeks to minimize "premature" accidental contacts with objects (see First Question and responses), the animals seek to make contact as quickly and as often as possible. The object pose and velocity are already uncertain, so contact can only make things better by providing information. In contrast to to the case with most robots, very light, grazing contacts - occurring almost anywhere, including on the back surfaces of the limbs or digits - are detected easily.

The manipulation behaviors resemble the "funnels" written about by [Burridge99; Full&Koditscheck99] --They can be, and frequently are, applied repeatedly in what looks like "flailing" until you realize that each iteration serves to reduce uncertainty in the pose of the object with respect to the goal (e.g. with respect to a achieving a stable grasp, or with respect to reaching the mouth).


Refs:

- C. Comer and P. Grobstein, "of Comparative Tactually Elicited Prey Acquisition Behavior in the Frog , Rana pipiens , and a Comparison with Visually Elicited Behavior," Journal Of Comparative Physiology, vol. 142, 1981, pp. 141-150.

- L.A. Gray, J.C. O'Reilly, and K.C. Nishikawa, "Evolution of forelimb movement patterns for prey manipulation in anurans.," The Journal of experimental zoology, vol. 277, 1997, pp. 417-24.

- R.R. Burridge, "Sequential Composition of Dynamically Dexterous Robot Behaviors," The International Journal of Robotics Research, vol. 18, 1999, pp. 534-555.

- R.J. Full and D.E. Koditschek, "Templates and anchors: neuromechanical hypotheses of legged locomotion on land.," The Journal of experimental biology, vol. 202, 1999, pp. 3325-32.

- T.E. Twitchell, "The automatic grasping responses of infants," Neuropsychologia, vol. 3, 1965, pp. 247-259.

 
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