Chapter 2. Prehension

Chapter 9 - Reevaluation and Future Directions 343
Experiments also suggest computational models. Effective
experiments have included perturbation studies, where microslips or
externally imposed changes in object properties are observed. Models
are needed for a better understanding of the methods in which the
computations may be performed. Analytic models of friction, and
levels of asperities in the contacting surfaces are needed, as are
computational models of force generation by the muscle, skin, and
‘passive’ viscoelastic properties of the hand. The weighting and
calibration of information across receptor types and sensory systems
is needed to understand better how exteroceptive and proprioceptive
systems are integrated with descending motor commands.
Computational and experimental models show the methods by
which feedback and feedforward control can work, depending on the
success of anticipatory movements. The role of practice and past
experience needs to be modelled for better understanding the role of
feedforward processes. If unexpected perturbations occur, feedback
control can make fine adjustments. At which levels feedforward and
fine adjustments can be implemented need to be defined more clearly.
Making explicit the influence of various constraints on the
environment/performer, the need for a common vocabulary between
experimentalists and roboticists is paramount. Much can be gained
through increased sharing and communication, using a triangular
approach to science.
This book is not comprehensive; many topics were left untouched.
Handedness, asymmetries (in hand and brain) and bimanual activities
(splitting the task demands) are glaring in their omission. Illusions
like the size-weight illusion were only alluded to. Postural (trunk,
hip, and lower limb) involvements were excluded from consideration,
as were parallels between locomotion and limb control. Little was
said about central and peripheral fatigue, and corresponding
adaptations. Detailed treatment of the research on special populations
has been left out. These include individuals with sensory or
neurological dysfunction, such as blindness, and patients with brain
lesions (e.g., apraxia, optic and motor ataxia). The effects of other
diseases (such as arthritis), conditions (like congenital anhydrosis)
and injuries (dislocations, carpal tunnel syndrome) on hand function,
are also notably absent.
It is our goal that this text be relevant to workers in the applied
sciences. There is much relevance here to human factors applications.
This includes the design of human-computer interfaces, other human-
machine interfaces (e.g., automobile control panels), hand tools, and
remote manipulators. For computer graphics, there are issues for