Abstract
Humans are high-dimensional, complex systems consisting of many components that must coordinate in order to perform even the simplest of activities. Many behavioral studies, especially in the movement sciences, have advanced the notion of soft-assembly to describe how systems with many components coordinate to perform specific functions while also exhibiting the potential to re-structure and then perform other functions as task demands change. Consistent with this notion, within cognitive neuroscience it is increasingly accepted that the brain flexibly coordinates the networks needed to cope with changing task demands. However, evaluation of various indices of soft-assembly has so far been absent from neurophysiological research. To begin addressing this gap, we investigated task-related changes in two distinct indices of soft-assembly using the established phenomenon of EEG repetition suppression. In a repetition priming task, we assessed evidence for changes in the correlation dimension and fractal scaling exponents during stimulus-locked event-related potentials, as a function of stimulus onset and familiarity, and relative to spontaneous non-task-related activity. Consistent with predictions derived from soft-assembly, results indicated decreases in dimensionality and increases in fractal scaling exponents from resting to pre-stimulus states and following stimulus onset. However, contrary to predictions, familiarity tended to increase dimensionality estimates. Overall, the findings support the view from soft-assembly that neural dynamics should become increasingly ordered as external task demands increase, and support the broader application of soft-assembly logic in understanding human behavior and electrophysiology.
Highlights
Humans are high-dimensional, complex systems consisting of many components that must coordinate in order to perform even the simplest of activities
Reaction times were analyzed with a repeated measures ANOVA with two within—subject factors, familiarity (Six levels: Exposures 1–6) and response (Two levels: Yes and No), with all reported values using the Greenhouse-Geisser correction for violation of sphericity
Post-hoc comparisons for the familiarity effect were Bonferroni corrected, and revealed a pattern where reaction times (RT) in Exp1 were significantly different than all other conditions, Exp6 was significantly different from all conditions except for Exp5 (p = 0.550), Exp4 and Exp5 were only significantly different from one another, and no other differences were significant
Summary
Humans are high-dimensional, complex systems consisting of many components that must coordinate in order to perform even the simplest of activities. What might seem to be a relatively simple behavior of producing a one syllable utterance, can require as many as 70 muscles to produce (Turvey, 2007) and more than seven cortical structures consisting of billions of neurons (Behroozmand et al, 2015). A number of the muscles involved in producing an utterance are involved in mastication, but there are discrepancies in muscular recruitment between the two tasks In this way, the particular components of the system are recruited for functionally specific purposes, but they maintain the ability to change as tasks and/or contexts change. The particular components of the system are recruited for functionally specific purposes, but they maintain the ability to change as tasks and/or contexts change This notion is precisely what is meant by suggesting that synergies are formed through soft-assembly mechanisms. The concept of synergies in this fashion has had a pervasive, primarily conceptual, history in physiology (Sherington, 1906; Bernstein, 1967; Turvey, 1977) and has even been argued as the key means for linking brain and behavior (Kelso, 2009)
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