Soft-assembly of sensorimotor function.

Von Holst (1939/73) proposed relative coordination as a general characteristic of sensorimotor functions like locomotion. Its functionality derives from striking a balance between independence versus interdependence among component activities, e.g., fin or leg oscillations in lipfish and centipede models, respectively. A similar balancing act in the Ising (1925) model was found to produce patterns of electron spin alignment, analogous to the soft-assembly of locomotive patterns. The Ising model analog to relative coordination is metastability, and Kelso (1995) hypothesized that metastability is essential to sensorimotor functions across levels and domains of analysis, from individual neurons to neural systems to anatomical components of all kinds. In the present survey, relative coordination and metastability are hypothesized to underlie the soft-assembly of sensorimotor function, and this hypothesis is shown to predict 1/f scaling as a pervasive property of intrinsic fluctuations. Evidence is reviewed in support of this prediction from studies of human neural activity, as well as response time tasks and speech production tasks.