In motor-respiratory coordination (MRC), people typically maintain frequency ratios that are from lower levels of a mathematical structure known as the Farey tree. A hypothesized mechanism for MRC is the visceral piston (Bramble & Carrier, 1983) - mechanical loading of the lungs due to footfalls, for example, imposes a rhythm on breathing. The occurrence of MRC in exercises in which there is no visceral piston (e.g., bicycling and wheelchair propulsion) implies that there are other mechanisms. We examined whether there is a perceptual basis for MRC. In Experiment 1, participants viewed simulated ratios side-by-side and, in a forced-choice paradigm, judged whether they were the same or different. In Experiment 2, participants performed ratios using feedback displays in which different ratios looked either the same or different. Lower-level ratios were less likely than higher-level ratios to be confused for other ratios. Ratios that could be distinguished perceptually were performed more accurately and less variably than ratios that appeared the same.

Abstract from:

Gonzales, L. M., Hessler, E. E., & Amazeen, P. G. (in press). Perceptual constraints on frequency ratio performance in motor-respiratory coordination. Ecological Psychology.