The functional integrity of the bimanual neuromotor system of Parkinson's disease (PD) subjects (stage II) compared to controls (2 × n = 16) was evaluated by measures of coordination stability of tapping in in-phase. anti-phase. and 90°-phase. Recently, intentional influence was modeled as an additive attractor function on the intrinsic dynamics, resulting in predictions tested by Scholz and Kelso (1990). In this study, the intentional influence was modulated by attaching cognitive meaning to the rhythmical pattern, which was expected to enhance the stability of coordination and, if effective, might be profitable to PD patients. Half of the PD subjects significantly lacked stability. They were less stable than controls, lost coordination at lower frequencies, and needed more time to switch between phase patterns. The reduction of stability was reflected in the progression of the disease. Cognitive meaning reduced variability of the single hands but not of relative phase, and no effect on switching time was found. The results suggest a weaker coupling strength between the limbs in PD patients lacking stability.
Martine H.G. Verheul and Reint H. Geuze
Rhythmic interlimb coordination arises from the interaction of intrinsic dynamics and behavioral information, that is, intention, memory, or external information specifying the required coordination pattern. This study investigates the influence of the content of memorized behavioral information on coordination in musically experienced and inexperienced participants. These groups are hypothesized to have different intrinsic dynamics for this task. Stability was assessed in a switching task (variability and switching time). The in-phase, antiphase, and 90°-phase difference were specified in a neutral and an ecologically relevant manner. Musicians showed more stable coordination than nonmusicians did. No interaction effect was found with memorized behavioral information. Behavioral information showed an interaction effect with phase pattern on coordination variability, with the strongest effect for the 90°-phase pattern. Switching time was affected largely in line with the findings for coordination variability. Participants showed an intraindividual preference for one type of gallop and one type of switch strategy, suggesting different hand roles.
Reint H. Geuze and Alex F. Kalverboer
This study is concerned with deficits in the ability to maintain an imposed rhythm in a tapping task and the possible sources of these deficits. Three groups of children between the ages of 7 and 12 with IQs above 75 participated: a group of children who were clumsy, a group who were dyslexic, and a control group whose reading and coordination were considered age appropriate. The children performed a series of “continuation” tapping tasks in which hand, speed, and rhythm of tapping were manipulated. The performance measure taken was the variability of tapping after the pacing signal had ceased. When the three groups were compared, the children who were clumsy showed a slightly increased variability across all tasks but no sign of lateralized performance differences. In contrast, the children who were dyslexic showed increased variability in only one task, involving the right hand. The results are discussed in relation to three different models of brain dysfunction.
M.J.M. Volman and Reint H. Geuze
The stability of single and bimanual (i.e., in-phase and antiphase) rhythmic finger movements was studied in 24 children with a developmental coordination disorder (DCD) and 24 matched controls from a dynamic pattern perspective. Stability was assessed by applying perturbations and measuring the time the system needed to return to its initial stability (i.e., the relaxation time). In addition, fluctuations of the patterns were measured. For antiphase coordination patterns, the frequency at which loss of stability occurred was also determined. Children with DCD displayed less stable single and bimanual rhythmic coordination patterns than control children. Further, within the DCD group, 9 children were identified as having particularly poor bimanual coordination stability. Individual differences suggested that variability of individual limb oscillations might have contributed to this poorer interlimb coordination stability. Findings were discussed in relation to a previous study on DCD in which the Wing-Kristofferson timekeeper model was applied.