1. Equilibrium Point Hypothesis (EPH)
Feldman (1966, 1986, …): λ-Model
Bizzi (1978, 1979, …): α- Model
∑F= : در حالت تعادل

3. EPH and Muscle Stiffness
F = k ( X – X0) :رابطه يك فنر (عضله)
K = σ (α )
X0 = β (λ)

7. Load Effect
βv = Θf - Td/σ

8. Evidence for EPH (Polit & Bizzi 1978-9)

9. EPH Generalization

11. Questions Unanswered? 1- Role of Motor Centers in the Brain?
2- Motor Learning?
3- Environmental Effects?

12. Fitt’s Law Speed-Accuracy Trade-off

13. Fitt’s Law Speed-Accuracy Trade-off

15. Fitt’s Law (cont.) MT = a + b [ log2 (2A/W) ] MT = Movement Time
ID ( Index of Difficulty) = A/W
log2: Inspired from information theory

16. Fitt’s Law (cont.)

17. Fitt’s Law (cont.)
Larger limb showed
more sensitivity

18. Learning & Fitt’s Law (cont.) Kelso (1984)
Slope was reduced to nearly zero following 40,000 trials.

19. Aging & Fitt’s Law (cont.) Kelso (1984)
Aging increases the slope

20. Modification to the Fitt’s Law
MT = a (A/W)b
Modification effect is minor (10%)