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Friedman, Jason; Brown, Scott; Finkbeiner, Matthew |
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Title |
Linking cognitive and reaching trajectories via intermittent movement control |
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2013 |
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Journal of Mathematical Psychology |
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57 |
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3-4 |
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140-151 |
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Decision making; Diffusion model; Reaction times; Arm movements; Submovements |
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Theories of decision-making have traditionally been constrained by reaction time data. A limitation of reaction time data, particularly for studying the temporal dynamics of cognitive processing, is that they index only the endpoint of the decision making process. Recently, physical reaching trajectories have been used as proxies for underlying mental trajectories through decision space. We suggest that this approach has been oversimplified: while it is possible for the motor control system to access the current state of the evidence accumulation process, this access is intermittent. Instead, we demonstrate how a model of arm movements that assumes intermittent, not continuous, access to the decision process is sufficient to describe the effects of stimulus quality and viewing time in curved reaching movements. |
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Park, J.; Pazin, N.; Friedman, J.; Zatsiorsky, V.M.; Latash, M.L. |
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Title |
Mechanical properties of the human hand digits: Age-related differences |
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Journal Article |
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2014 |
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Clinical Biomechanics |
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29 |
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2 |
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129–137 |
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hand; aging; friction; apparent stiffness; damping |
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Background
Mechanical properties of human digits may have significant implications for the hand function. We quantified several mechanical characteristics of individual digits in young and older adults.
Methods
Digit tip friction was measured at several normal force values using a method of induced relative motion between the digit tip and the object surface. A modified quick-release paradigm was used to estimate digit apparent stiffness, damping, and inertial parameters. The subjects grasped a vertical handle instrumented with force/moment sensors using a prismatic grasp with four digits; the handle was fixed to the table. Unexpectedly, one of the sensors yielded leading to a quick displacement of the corresponding digit. A second-order, linear model was used to fit the force/displacement data.
Findings
Friction of the digit pads was significantly lower in older adults. The apparent stiffness coefficient values were higher while the damping coefficients were lower in older adults leading to lower damping ratio. The damping ratio was above unity for most data in young adults and below unity for older adults. Quick release of a digit led to force changes in other digits of the hand, likely due to inertial hand properties. These phenomena of “mechanical enslaving” were smaller in older adults although no significant difference was found in the inertial parameter in the two groups.
Interpretations
The decreased friction and damping ratio present challenges for the control of everyday prehensile tasks. They may lead to excessive digit forces and low stability of the grasped object. |
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0268-0033 |
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73 |
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Shaklai, S.; Mimouni-Bloch, A.; Levin, M.; Friedman, J. |
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Title |
Development of finger force coordination in children |
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2017 |
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Experimental Brain Research |
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235 |
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12 |
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3709–3720 |
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Coordination is often observed as body parts moving together. However, when producing force with multiple fingers, the optimal coordination is not to produce similar forces with each finger, but rather for each finger to correct mistakes of other fingers. In this study, we aim to determine whether and how this skill develops in children aged 4-12 years. We measured this sort of coordination using the uncontrolled manifold hypothesis (UCM). We recorded finger forces produced by 60 typically developing children aged between 4 and 12 years in a finger-pressing task. The children controlled the height of an object on a screen by the total amount of force they produced on force sensors. We found that the synergy index, a measure of the relationship between “good” and “bad” variance, increased linearly as a function of age. This improvement was achieved by a selective reduction in “bad” variance rather than an increase in “good” variance. We did not observe differences between males and females, and the synergy index was not able to predict outcomes of upper limb behavioral tests after controlling for age. As children develop between the ages of 4 and 12 years, their ability to produce negative covariation between their finger forces improves, likely related to their improved ability to perform dexterous tasks. |
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1432-1106 |
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Shaklai2017 |
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86 |
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Kaufman-Cohen, Y.; Levanon, Y.; Friedman, J.; Yaniv, Y.; Portnoy, S. |
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Home exercise in the dart-throwing motion plane after distal radius fractures: A Pilot Randomized Controlled Trial |
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2020 |
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Journal of Hand Therapy |
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Portnoy, S.; Mimouni-Bloch, A.; Rosenberg, L.; Offek, H.; Berman, T.; Kochavi, M.; Orman, G.; Friedman, J. |
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Graphical Product Quality and Muscle Activity in Children With Mild Disabilities Drawing on a Horizontally or Vertically Oriented Tablet |
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2018 |
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American Journal of Occupational Therapy |
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Am J Occup Ther |
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72 |
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6 |
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1-7 |
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OBJECTIVE. We compared performance level and muscle activity patterns during shape copying and tracing in two positions, while sitting at a desk and while standing in front of a wall, between typically developing (TD) preschool children and children with mild disabilities (MD).
METHOD. Twenty-two TD children (8 boys, 14 girls; mean [M] age 5 5.2 yr, standard deviation [SD] 5 0.1) and 13 children with MD (9 boys, 4 girls; M age 5 4.9 yr, SD 5 0.5) participated in this study.
RESULTS. The children performed faster and smoother movements when copying shapes on the vertical surface, with no reduction of accuracy, than on the horizontal surface. Children with MD exerted their upper trapezius while performing the short tasks on the vertical surface compared with their muscle activity on the horizontal surface.
CONCLUSION. Incorporating short copying or drawing tasks on a vertical surface may increase the control of proximal muscles and ease graphomotor performance in children with MD. |
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0272-9490 |
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Penn State @ write.to.jason @ |
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91 |
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