|Series| Theories of CRM
What is Rhythm Setting?
Wenderoth et al. (2002) suggest a separate mechanism is used by the central nervous system to produce unknown phases of coordinated rhythmic movement (CRM). They call this rhythm setting (RS).
The interest of the RS approach comes from the world of trained musicians. This is a technique that is used by musicians to produce both known and unknown polyrhythms. When applying this technique to a new movement phase, the authors claim a staggering result (though I can find no direct empirical basis for this). Both musicians and non-musicians can be trained to produce a new movement phase within a very short space of time (relative to how long it normally takes).
An Attempt to Understand the Transfer Between Limbs
Rhythm setting uses the language of ratios in an attempt to understand why there is a transfer of learning between limbs (its symmetrical partner), i.e. learning of 90° would transfer to the learning of 270° (Zanone & Kelso, 1997).
Breaking Down the Ratio Talk
The authors describe their ratios in the following fashion. 90° is said to have a ratio of 1/1 and 60°, 2/1. These ratios are represented below graphically. The unshaded sections are when the limbs are moving in the same direction and the shaded sections are when the limbs are not moving in the same direction. The ratios are representative of only half a cycle. In 90° each half cycle contains one unidirectional and one non-unidirectional movement, creating the 1/1 ratio. In 60° each half cycle contains two unidirectional movements and only one non-unidirectional movement, creating a 2/1 ratio.
The point the authors are trying to make is that these ratios aren’t independent of a particular limb (or movement). They suggest that the reason there is a transfer between certain coordination patterns is due to the sharing of a rhythm setting ratio and that the learning process is closely tied to the learning of the rhythm setting ratio rather than the phase itself.
To test this theory the authors split participants into 1 of 5 groups dependent on the to-be-learned pattern of movement (36°, 60°, 90°, 120° & 144°).
We were interested also in whether non-instructed participants with no musical background would unconsciously use this mechanism (RS). We hypothesised that if the rhythm-setting is used, especially the ɸ = 90°, RS = 1/1 group should perform better than the ɸ = 36°, RS = 4/1 and the ɸ = 144° RS = 1/4 group. (Wenderoth et al., 2002. pg 15).
The results did not support this hypothesis. Wenderoth et al. discredit the use of RS as an unconscious mechanism adopted for learning new coordinated rhythmical phases. Instead, they suggest ‘that the required movement is represented as a spatio-temporal relation between the hands, rather than as a relatively abstract “timing-characteristic” of the coordination pattern’.
As 90° (RS = 1/1) is described as having a simpler ratio than say, 36° (RS = 4/1) and 60° (RS= 2/1). The logic was that if RS was used unconsciously a 1/1 ratio would be easier to learn than other more complex rhythms. The results led the authors to discredit the idea of RS on the grounds that 90° was not performed better than 36° or 144°. That said, the concept that known rhythm-setting ratios may be reused by the organism (transfer of learning) to produce unknown patterns of the same ratio is not tested here.
Wenderoth, N., Bock, O., & Krohn, R. (2002). Learning a new bimanual coordination pattern is influenced by existing attractors. Motor Control, 6, 166–182.
Zanone, P., & Kelso, J. (1997). Coordination Dynamics of Learning and Transfer: Collective and Component Levels. J Exp Psychol Hum Percept Perform, 23(5), 1454–1480.