To controlforceaccurately under a wide range of behavioral conditions, the central nervous system would either require a detailed, continuously updated representation of the state of each muscle (and the load against which each is acting) or else force feedback with sufficient gain to cope with variations in the properties of the muscles and loads. The evidence for force feedback with adequate gain or for an appropriate central representation is not sufficient to conclude that force is the major controlled variable in (...) normal limb movements.Morton's hypothesis, thatlengthis controlled by a follow-up servo, has a number of difficulties related to the delays, gains, variability, and specificity in feedback pathways comprising potential servo loops. However, experimental evidence is consistent with these pathways providing servo assistance for some movements produced by coactivation of α- and static γ-motoneurons. Dynamic γ-motoneurons may provide an additional input for adaptive control of different types of movements.The idea that feedback is used to compensate for changes in musclestiffnesshas received experimental support under static postural conditions. However, reflexes tend to increase rather than decrease the range of variation in muscle stiffness during some cyclic movements. Theoretical problems associated with the regulation of stiffness are also discussed. The possibilities of separate control systems forvelocityorviscosityare considered, but the evidence is either negative or lacking. I conclude that different physical variables can be controlled depending on the type of limb movement required. The concept of stiffness regulation is also useful under some conditions, but should probably be extended to the regulation of the visco-elastic properties (i.e., the mechanical impedance) of a muscle or joint. (shrink)

During the past two decades, philosophers of biology have increasingly turned their attention to mechanisms of biological phenomena. Through analyses of mechanistic proposals advanced by biologists, the goal of these philosophers is to understand what a mechanism is and how mechanisms explain. These analyses have generally focused on mechanistic proposals for phenomenon that occur at the cellular or sub-cellular level, such as synapse firing, protein synthesis, or metabolic pathway operation. Little is said about the mechanisms of the macromolecular reactions that (...) underpin these phenomena. These reactions comprise a diverse family of reaction types, and include protein folding, macromolecular complex formation, receptor-ligand interactions, and enzyme catalysis. In this paper, I develop an account of mechanism that focuses exclusively on macromolecular reactions. I begin by reviewing how mechanism is understood in enzymology, and how mechanistic concepts of enzymology apply to macromolecular reactions in general. We will see that the mechanism of a macromolecular reaction is most accurately described as a progression of reaction intermediates, where the evolution of intermediates, from one to the next, is characterized by an energetic coupling between chemistry and protein dynamics. I then make the case that this description necessitates a grounding in a process ontology. To describe the mechanism by which a macromolecular reaction occurs is to describe a process. (shrink)

Enzymes are protein catalysts of extraordinary efficiency, capable of bringing about rate enhancements of their biochemical reactions that can approach factors of 1020. Theories of enzyme catalysis, which seek to explain the means by which enzymes effect catalytic transformation of the substrate molecules on which they work, have evolved over the past century from the “lock-and-key” model proposed by Emil Fischer in 1894 to models that explicitly rely on transition state theory to the most recent theories that strive to provide (...) accounts that stress the essential role of protein dynamics. In this paper, I attempt to construct a metaphysical framework within which these new models of enzyme catalysis can be developed. This framework is constructed from key doctrines of process thought, which gives ontologic priority to becoming over being, as well as tenets of a process philosophy of chemistry, which stresses environmentally responsive molecular transformation. Enzyme catalysis can now be seen not as enzyme acting on its substrate, but rather as enzyme and substrate entering into a relation which allows them to traverse the reaction coordinate as an ontologic unity. (shrink)

This interview with media anthropologist, Rebecca L. Stein, conducted by Noa Levin and Andrew Fisher in Spring 2023, takes her recent book Screenshots: State Violence on Camera in Israel and Palestine (2021) as its starting point in order to explore issues of state violence and the militarization of social media in Israel/Palestine. This book marks the culmination of a decade-long research project into the camera dreams introduced by digital imaging technologies and the fraught histories of their disillusionment. Stein discusses the (...) way her research has critically conceptualized the recent history of hopes invested in the digital image in this geopolitical context, by the occupier as much as the occupied, and charts the failures and mistakes, obstructions and appropriations that characterize the conflicted visual cultures of Israel/Palestine. (shrink)

After fifteen years as an award-winning educator, Ryan Stein knows this: when you make the school experience about fostering genuine human connection, students don't just succeed-they thrive. In this part-guidebook, part-memoir, Ryan shares the best ideas and stories from his groundbreaking educational philosophy with anyone seeking to make a positive difference in a student's life. "Lifeline 65" is as joyful as it is useful, packed full of wit, humor, and heart. Try even one strategy and you'll find your students more (...) engaged, confident, and eager to excel, from elementary school to college and beyond. All you have to do is begin. (shrink)

Is the reason that majorities exert an undue influence on the actions of individuals revealed through changes in subjective experience? Using an adaptation of the response interference paradigm in which participants are trained to introspect on their own experience of conscious conflict, two studies reported here show that the mere act of recalling counter-majority stances or opinions is associated with stronger subjective effects than recalling stances or opinions that coincide with majorities. Thus, an intention to conform to a majority seems (...) to interfere with people’s recall of their own stance or opinion. These results provide novel evidence for recent yet under-supported suggestions that majorities can influence individuals even when it is improper or illogical because human social cognition is primarily and involuntarily cooperative at the implicit level. (shrink)

The 1953 discovery of the DNA double helix (Watson and Crick 1953) and the elucidation of the molecular basis for inheritance marked the dawn of a new era. When the U.S. Human Genome Project was in...