Tim Eakin

Unique estimation of Gompertz parameters with mortality deceleration rate

In this paper we have proven uniqueness theorems for estimation of the age-dependent parameter @a in the Gompertz survival model with a mortality deceleration rate, in the absence of age-specific mortality data. We obtained estimations dependent on and uniform in the population size N.

Decoupling tremor and volitional force control factors in analyses of motor task performance

A frequency domain filtering protocol is described for separating force contributions from tremor and fine motor control when both factors are present during performance of a goal-oriented task. This method partitions the frequency domain after Fourier transformation of time series data. Amplitudes within a range are divided by or substituted with analogous values from a defined task function to obtain representations of the contribution of a particular factor or that remaining in the absence of the factor. Filtered data can then be used for independent characterization of each factor with respect to frequency power spectra or time series properties.

Age and practice effects on inter-manual performance asymmetry

Manual dexterity declines with increasing age, however, the way in which inter-manual asymmetry responds to aging is unclear. Our purpose was to determine the effect of age and practice on inter-manual performance asymmetry in an isometric force pinch line tracing task that varied in difficulty within segments. Thirty right-handed participants, five males and five females in each of three age groups, young (Y20), young–old (O70), and old–old (O80), practiced an isometric force pinch task for 10 trials with each hand on each of five consecutive days. Inter-manual performance asymmetry of the right and left hands was analyzed with a repeated measures analysis of variance (ANOVA) of asymmetry with age groups, practice, task difficulty, and hand as factors. The within-individual magnitude of asymmetry was also analyzed with a repeated measures ANOVA of manual asymmetry calculated as an asymmetry index (AI). Post hoc pair-wise comparisons were performed when significance was found. We observed no inter-manual performance asymmetry on this isometric tracing task among any of the age groups, either in the hand performance differences or in the magnitude of the AI. Age and practice interacted in terms of manual performance: the Y20 and O70 group improved accuracy and task time across the 5 days of practice but the O80 group did not. However, practice did not differentially affect the AI for accuracy or task time for any group. Accuracy of performance of the two hands was differentially affected by practice. All age groups exhibited poorer performance and larger AIs on the most difficult segments of the task (3 and 6) and this did not change with practice.

Dynamic variability of isometric action tremor in precision pinching.

Evolutionary development of isometric force impulse frequencies, power, and the directional concordance of changes in oscillatory tremor during performance of a two-digit force regulation task was examined. Analyses compared a patient group having tremor confounding volitional force regulation with a control group having no neuropathological diagnosis. Dependent variables for tremor varied temporally and spatially, both within individual trials and across trials, across individuals, across groups, and between digits. Particularly striking findings were magnitude increases during approaches to cue markers and shifts in the concordance phase from pinching toward rigid sway patterns as the magnitude increased. Magnitudes were significantly different among trace line segments of the task and were characterized by differences in relative force required and by the task progress with respect to cue markers for beginning, reversing force change direction, or task termination. The main systematic differences occurred during cue marker approach and were independent of trial sequence order.

Existence of Gompertz parameters with mortality deceleration rate and their asymptotic formulae for a large population

In this paper we provide an interval of existence of mortality rate parameters A and @a, and their asymptotic expressions in a Gompertz survival model with mortality deceleration rate, in the absence of age specific mortality data.

Force and Directional Force Modulation Effects on Accuracy and Variability in Low-Level Pinch Force Tracking

ABSTRACT The authors investigated how varying the required low-level forces and the direction of force change affect accuracy and variability of force production in a cyclic isometric pinch force tracking task. Eighteen healthy right-handed adult volunteers performed the tracking task over 3 different force ranges. Root mean square error and coefficient of variation were higher at lower force levels and during minimum reversals compared with maximum reversals. Overall, the thumb showed greater root mean square error and coefficient of variation scores than did the index finger during maximum reversals, but not during minimum reversals. The observed impaired performance during minimum reversals might originate from history-dependent mechanisms of force production and highly coupled 2-digit performance.