Long-range correlations are often manifested in the form of 1/fβ noise in a series of repeated measurements of the same neural or behavioral variable. Recent work has demonstrated that the magnitude and nature of these long-range correlations reliably capture individual differences and variation in task performance. In sensorimotor timing experiments, task characteristics such as tapping or circle drawing affect these long-range correlations during the production of isochronous time intervals. Such correlations are highly reproducible across multiple trials for the same task (...) but do not correlate between tasks. In the present experiment, we investigate whether two behavioral variables that are simultaneously controlled by the same participant in a given experimental condition can show such differentially organized fluctuations. In order to answer this question, 13 participants were asked to produce repetitive movements with their right index finger at a specified time interval and a specified force in the absence of an auditory metronome and visual feedback of force levels following a synchronization-continuation paradigm. Although participants showed high levels of consistency in the long-range correlations for each task component separately over multiple trials/observations, the long-range fluctuations for force and timing were found to show no correlations with each other for each participant. Cross recurrence quantification analyses revealed that there was limited shared structure between the timing and force time series data. Taken together, these results suggest that complex systems can organize multiple processes in a relatively independent manner while maintaining a high degree of reliability within one task parameter. (shrink)

It is proposed here that Webb's ideas about robots as possible models of animals need some rethinking. In our view, even though widely used biorobotics strategies are fairly successful at reproducing the macroscopic behavior of biological systems, there are still several problems unresolved on the side of robotics as well as biology. Both mathematical and hardware-like robotics models should be feasible physiologically. Control principles elaborated in robotics are not necessarily applied to biological control systems. Although observations of flying birds inspired (...) aerodynamics and thus modern airplanes, little knowledge has been added to the neurophysiological principles underlying flight in birds. Chess playing computers might outperform most chess players, but they cannot be considered as physiologically feasible models of human thinking. (shrink)

Grush has proposed a fairly comprehensive version of the idea of internal models within the framework of the emulation theory of representation. However, the formulation suffers from assumptions that render such models biologically infeasible. Here I present some problems from physiological principles of human movement production to illustrate why. Some alternative views to emulation are presented.