ReviewLaws of nature that define biological action and perception
Introduction
The history of the physical approach to biological problems is rather old and rich. It can be traced back at least to studies of von Helmholtz in the middle of the nineteenth century. Arguably, one of the most influential books in this area was written by Schrödinger [1]. In that book, he emphasized the importance of thermodynamics for biological functions and introduced the idea that biological system were able to reduce their entropy at the expense of the environment. This approach has been developed in the field of brain cognitive functions under the assumption that energy represents their universal currency [2], [3], [4], [5], [6], [7], [8]. In particular, recent studies by Friston and colleagues [9], [10] assume that the brain functions to minimize predictive errors (cf. brain as a predictive organ, [11]) leading to free energy minimization and reduction of entropy. This approach has been developed using tools from Bayesian statistics.
The approach taken in this paper can be called “bottom-up”. We start from the interface between an animal and physical laws acting in the inanimate world and try to identify biology-specific laws of nature in living systems that allow to explain specific features of motor and other behaviors. Biological movements are perfectly suited for this purpose because they function in direct contact with the environment and can be studied objectively using the apparatus of classical mechanics. Further in this paper we make a cautious step to analysis of perception. Unlike movements, percepts are not directly observable and are commonly estimated using indirect methods such as psychophysical scales, matching paradigms, etc. As a result, inferences made based on such indirect data should always be taken with a grain of salt. By the end of the paper, we only dare to glimpse into possible developments of this approach to cognitive functions, which, as of now, remain beyond the author's comprehension.
Section snippets
Universal and biology-specific laws of nature
It is useful to begin exposition of the physical approach to biological objects and processes with a few basic definitions. Laws of nature are compact descriptions of our experiences with particular classes of objects and processes. They are usually limited in their scope. For example, the classical Newton Second Law () is applicable to objects with inertia, the Hooke's Law () – to objects that deform and store potential energy (springs), etc. Commonly, laws of nature are expressed
Control of actions with referent coordinates
The idea of producing actions with time changes in parameters, such as λ, has been generalized for the control of individual joints, extremities, and the whole body in the form of the hypothesis of neural control with spatial referent coordinates, RCs (RC-hypothesis, reviewed in [13], [19]). According to the RC-hypothesis, any action starts with defining spatial RC at a task-related effector level, which can be related to an extremity (during reaching), a hand (during prehension), or the whole
Where do stable percepts come from?
Imagine that you are holding your arm in the air in a certain configuration and then co-contracting strongly all arm muscles trying to avoid moving the arm (your eyes are closed!). This is very easy to do, and you would have veridical feeling that the arm configuration has not changed. Where does this stable percept come from? Consider, for simplicity, only one joint, for example the elbow joint. All proprioceptors in all the muscles, tendons, and joint capsule will change their firing rate
This framework is productive and robust
Any scientific hypothesis is as good as its ability to generate non-trivial, experimentally testable predictions (of course, in addition to being able to account for known phenomena). The key word “non-trivial” means that most colleagues would not make such predictions based on alternative hypotheses in the field. Drawing such predictions can be seen as attempts to disprove the hypothesis. If many such attempts fail, the hypothesis may be accepted as a viable theory.
So far, a large number of
Movement disorders
There are several examples of application of the described line of thinking to disordered movements. Note that the control with time functions RC(t) may be viewed as using a set of tools (RC shifts) to achieve certain goals under specific external conditions. Metaphorically, this can be compared to using the steering wheel, the gas pedal, and the brakes to drive from State College to New York. There are situations when tools become altogether broken or limited in their range of use. In
Declaration of Competing Interest
The author declares that he has no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
I am very much grateful to my former and current students, postdoctoral fellows, and visiting researchers who performed many of the studies reviewed in this paper. In particular, my special thanks go to Valters Abolins, Satyajit Ambike, Cristian Cuadra, Frederic Danion, Paulo de Freitas, Ali Falaki, Sandra Freitas, James Hirose, Hang Jin Jo, Ziga Kozinc, Sheng Li, Daniela Mattos, Halla Olafsdottir, Jaebum Park, Behnoosh Parsa, Joseph Ricotta, Stanislaw Solnik, Alexandre Terekhov, Wiktoria
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2022, Human Movement ScienceCitation Excerpt :That is, the controller governs only task level variables of motor actions, and the features such as the activation and covariation of individual finger forces seem to be a secondary consideration within the scope of control by the CNS. Indeed, the pattern of covariation between the variables at a higher level does not specify the unique combination of the lower-level variables in a redundant biological system (Latash, 2020a). Previous theoretical studies (Cutkosky & Howe, 1990; Iberall, 1997) and experimental studies on hand and finger actions (Baud-Bovy & Soechting, 2001; Santello & Soechting, 1997; Shim et al., 2003) have suggested a hierarchical control of multi-digit prehension based on the notions of the virtual finger (VF) and individual finger (IF), i.e., at the higher level (VF level) the thumb and VF are coordinated to satisfy task mechanics whereas at the lower level (IF level) the individual fingers are coordinated to generate a desired task-specific outcome of the virtual finger.