Chapter 2. Prehension

Chapter 8 - Constraints on Human Prehension 325
as an input, influencing the selection of the grasp and reach
strategy.
5. Object Properties-not time varying if inanimate or moving.
Changes between grasps, thus acting as an input, influencing
the selection of the grasp and reach strategy
6. BiomechanicallMechanical--laws of physics, captured in a
variety of time-varying functions, can become part of the
processing algorithm (rule or function being computed).
7. Neural--Anatomy: not time varying within the time scale of
the current reach and grasp. Can change within a person's
lifetime, affecting the topology of the processing circuits.
Physiology: time varying within the time scale of the current
reach and grasp, affecting the processing algorithm (its
implementation). Changes within a person's lifetime.
8. Perceptual--location and response characteristics of receptors
not generally time varying within the time scale of the current
reach and grasp. Changes within a person's lifetime, thus
acting as an input, influencing the selection of the grasp and
reach strategy.
9. AnatomicaVPhysiological--Anatomical: not time varying
within the time scale of the current reach and grasp. Changes
within a person's lifetime, thus acting as an input, influencing
the selection of the grasp and reach strategy. Physiological:
time varying within the time scale of the current reach and
grasp, acting as inputs.
10. Evolutionary--not time varying within the time scale of the
current reach and grasp or within a person's lifetime.
Affecting the anatomy and physiology of both the armhand
and topology/substrate of the brain.
Summarizing, the sources of constraints that are time-varying
functions within a particular grasp are the biomechanical and the
physiological aspects of the &and and the brain. The sources of
constraints that act as inputs into a decision process for selecting a
grasp strategy are: hand anatomy, perceptual constraints, object
properties, functional, informational, motivational, and social/cultural.
Constraints that are part of the processing algorithm (Marr's level 2)
are the (bio)mechanical. Constraints that are part of the processing
implementation (Marr's level 3) are neural, anatomy, and physiology.