Ce. Peper et Pj. Beek, DISTINGUISHING BETWEEN THE EFFECTS OF FREQUENCY AND AMPLITUDE ON INTERLIMB COUPLING IN TAPPING A 2 3 POLYRHYTHM/, Experimental Brain Research, 118(1), 1998, pp. 78-92
Rhythmic interlimb coordination is characterized by attraction to stab
le phase and frequency relations. Sudden, unintended transitions betwe
en such coordination patterns have been observed in iso-and multifrequ
ency tasks when movement frequency was gradually increased. These tran
sitions have been accounted for by modeling the two limbs as nonlinear
ly coupled oscillators. The prevailing form of the coupling function i
s based on time derivatives, but an alternative formulation can be der
ived by incorporating time delays. These time delays may be related to
the neurophysiological delays associated with the use of kinesthetic
afferences. The two ways of deriving coupling functions for interlimb
coordination allow for different predictions with respect to the effec
ts of movement frequency and amplitude on the strength of interaction
between the limbs. In the current experiment, the effects of amplitude
and frequency were dissociated experimentally, so as to arrive at an
empirically motivated choice between the two ways of formalizing inter
limb coupling. Subjects tapped the polyrhythm 2:3 at five different fr
equencies under three amplitude conditions. Whereas no effects of ampl
itude were observed, the strength of interaction between the hands dec
reased with increasing movement frequency. These results support the t
ime-delay version of the model, in which differential (loss of) stabil
ity of coordination modes results from differential dependence on move
ment amplitude, but overall coupling strength is related reciprocally
to movement frequency squared. This version of the model was related t
entatively to three proposed aspects of interlimb coordination: (1) ne
urophysiological delays associated with the use of kinesthetic afferen
ces; (2) rate-dependent decrease pattern stability; and (3) differenti
al entrainment influences of kinesthetic signals.