Biomedical subjects

J H Cocatre-Zilgien

Publications and source records attributed to J H Cocatre-Zilgien.

5 recordsLinked to original sources

PubMed1995

An approach to validation of a leg simulation by the comparison of two dynamic models.

The dynamics of a jointed leg were simulated using two different models, one based on a recursive Newton-Euler method and one on a closed-form Lagrange method. To validate the models, the simulations were run in parallel and the intermediate steps and output of the two methods were compared to one another to reveal the presence and locations of errors. Sources of error and the use of this method for the detection of errors are discussed. Some errors could not have been detected using only a single simulation.

Acceleration↗

PubMed1992

Identification of bursts in spike trains.

A computer algorithm to identify 'bursts' in trains of spikes is described. The algorithm works by constructing a histogram of interspike intervals, then analyzing the histogram to detect the critical interval value in the distribution that represents the break between short intervals within a burst and the longer intervals between bursts. When such a value is found, it is used as the 'threshold' to determine those intervals in the spike train that lie within a burst and those that lie between bursts and, thereby, to identify the beginning and end of each burst in the train. The validity of the bursts is evaluated with a chi-square test. The performance of the algorithm and how it can be assessed is discussed.

Algorithms↗

PubMed1990

A slope-based approach to spike discrimination in digitized data.

A spike discrimination algorithm based on the analysis of spike up- and down-slopes can advantageously replace those based only on amplitude with a minimal increase of programming complexity and processing time. Such an algorithm was developed to sort muscle depolarizations from nerve spikes in electromyograms in insects. It could also be used to sort spikes according to their direction of travel in bipolar recordings from mixed nerves.

Action Potentials↗

PubMed1988

Empirical evaluation of two-sample statistical tests for differences of stepping phase during insect walking.

In order to determine which statistical tests can validly be applied to data that describe a temporal relationship between two or more repetitive movements by an animal, we evaluated empirically seven two-sample tests that seemed potentially useful: Student's t test, the Watson Williams test for means, the variance-ratio F test, the Watson Williams test for the concentration parameter k, the Wallraff test, the Mann Whitney test and the Watson U2 test. Evaluations were carried out on the timing (phases) of bursts of muscular activity in one leg relative to those in another during free walking in cockroaches. Each statistical test was evaluated by dividing randomly a single parent set of data into two subsets, each subset containing about half the original data set. This division was repeated 400 times, thus generating 400 different pairs of subsets. Each statistical test was used separately on the pairs of subsets to test the null hypothesis that the two samples of each pair came from the same population; this procedure generated 400 statistics for each test, one for each pair of subsets. An estimate of the reliability of each statistical test was obtained by comparing the number of times the test actually indicated a significant difference between subsets to the number of times it might be expected to do so out (20 out of 400 when tested at the 5% level of significance). This procedure was repeated on ten different sets of data. The outcome of the evaluation suggested that, from an empirical point of view, Student's t, the Mann Whitney, the Wallraff and the Watson U2 tests may be useful in assessing differences among the data we analyzed. The variance-ratio F test and the Watson Williams test for the concentration parameter k were clearly not usable. The Watson Williams test for means might be useful in some circumstances. Performing an arcsine transformation of the data did not significantly alter these results. Possible causes of the inapplicability of some of these tests to phase data are discussed.

Animals↗

PubMed1988

Individual differences and variability in the timing of motor activity during walking in insects.

The uniformity of the neural physiology of an animal population is a fundamental, rarely tested assumption in most neurophysiological work. In this study, the variability of the timing between the movements of pairs of legs during free walking in cockroaches was assessed. Phases (a measure of timing) of motor bursts in muscles of legs in the American cockroach, Periplaneta americana, were calculated for insects walking straight over a flat, level surface. Student's t, Wallraff, Mann Whitney and Watson U2 two-sample tests were used to compare the phases of motor bursts of the same pairs of legs in different insects. The comparisons showed that in spite of the homogeneity both of the animal population and of the conditions under which the insects walked, most of the inter-leg phases of the animals that were compared were significantly different statistically. Further testing of greater numbers of insects using analysis of variance to test for population uniformity confirmed that the insects we tested were not members of a single statistical population with respect to the timing of motor bursts of the legs during walking. We infer that this unexpectedly large variability in a population thought to be relatively homogeneous reflects subtle but biologically significant differences between animals. The possible sources of these differences and their consequences for the study of behavior and its physiological basis are discussed.

Animals↗