What is prehension? - Noriko Kamakura

What is prehension?

"A grasp is every static hand posture with which an object can be held securely with one hand, irrespective of the hand orientation". - Feix et al. (2016, p. 67)

"Grip is when you move your arm all around and the object still deosnt' fall out" - Kamakura et a. (2022, p. 30)

So "hook" is not a form of grip according to them. depends on what hopok is though...

 

What is "Taxonomy of Prehension"? - Noriko group observed 700+ grips from ~100 objects and 7 healthy subjects.

1. Power Grips: Grips in which the contact region ran from the palm into the palmar surfaces of the fingers

2. Intermediate Grips: Grips that involved the radial surface of at least one of the fingers

3. Precison Grips: Grips in which the contact was mainly on the palmar surfaces of the thumb and at least some of the fingers

4. Thumbless Grip: Only one type; Grip in which thumb plays no part and a light object is secured between adjacent fingers

 

How do we choose our grips?

• Object's size and shape
• How it is placed beforehand
• How big and strong your hand is
• Your habits
• What kind of mood you're in

Relative geometry (size, shapet) of object and hand 

Contact features: object surface roughness and texture, hand surface

Relative physical features (temperature, mass, muscle strength)

Subject's habits, tendency (ex. willing to grab sharp things...?), kind of mood