Quantitative Analysis of Rapid Pointing Movements in Cree Subjects Exposed to Mercury and in Subjects with Neurological Deficits

To quantify rapid and precise proximo–distal movements, we have developed a simple system (eurythmokinesimeter or EKM) which requires the subject to touch alternately the center of proximal and distal targets with a stylus. Ninety-six participants, including 30 controls subjects, 36 Cree subjects exposed to mercury, 21 subjects with Parkinson disease, 6 with presumed cerebellar deficit, and 3 with essential tremor, participated in the study. A total of nine measures, including precision, imprecision, contact duration, unsureness, tremor, transit time, irregularity, speed, and Fittsʹ constant, were calculated. Test–retest reliability was above 0.8 for most measures and above 0.9 for many measures. Correlations between measures and number of outliers with respect to the control group distribution for each measure were used to reduce the set of measures to five (i.e., precision, imprecision, tremor, Fittsʹ constant, and irregularity). An ANOVA on the three largest groups generated significant results for tremor, Fittsʹ constant, and irregularity between the Cree and the control subjects and on Fittsʹ constant and irregularity between the subjects with Parkinsonʹs disease and the control subjects. Three subgroups of the same mean age composed of six subjects each were selected. One was composed of Cree subjects with the highest level of mercury exposure, another with Cree subjects having a low level of mercury exposure, and a third with control subjects. An ANOVA on these three groups revealed a significant difference between both groups of Cree subjects and the control group for Fittsʹ constant and irregularity. These preliminary results suggest that the EKM system is able to discriminate the performance of different groups of subjects.