Biomedical subjects

A C Sittig

Publications and source records attributed to A C Sittig.

4 recordsLinked to original sources

PubMed1991

Misdirections in slow goal-directed arm movements and pointer-setting tasks.

Information about the direction of the virtual line between two positions in space (directional information) is used in many decision-making and motor tasks. We investigated how accurately directional information is processed by the brain. Subjects performed two types of task. In both tasks they sat at a table. In the first task they had to move their hand slowly and accurately from an initial position 40 cm in from of them to visually presented targets at a distance of 30 cm from the initial position (movement task). We analysed the initial movement direction. In the second task subjects had to position pointers in the direction of the targets as accurately as they could (perceptive task). We found that in the movement task the subjects started the movements to most targets in a direction that deviated consistently from the direction of the straight line between initial position and target position. The maximum deviation ranged from 5-10 degrees for the various subjects. The mean standard deviation was 4 degrees. In the perceptive task the subjects positioned the pointer in similarly deviating directions. Furthermore, we found that the maximum deviation in the pointer direction depended on the length of the pointer: the smaller the pointer, the larger the consistent deviations in the pointer direction. The shortest pointer showed deviations comparable to the deviations found in the movement task. These findings suggest that the deviations in the two tasks stem from the same source.

Arm↗

PubMed1990

Reconstruction of the Frank vectorcardiogram from standard electrocardiographic leads: diagnostic comparison of different methods.

Three methods for reconstructing the Frank VCG from the standard 12-lead ECG were studied. The first was based on multivariate regression, the second on a model of the cardio-electrical activity, and the third method used a quasi-orthogonal set of ECG leads. The methods were evaluated on a test set of 90 cases by a numerical distance measure and by the agreement in diagnostic classification of the original and reconstructed VCGs. The original and reconstructed VCGs were presented separately and in random order to three referees. Eighteen of the original VCGs were presented three times to estimate the intra-observer agreement. Kappa statistics were used to quantify the agreement between diagnostic classifications. Separately, one referee was simultaneously presented the original VCG and its three reconstructions for all cases. Each reconstruction VCG was classified as either diagnostically 'same' as the original, 'borderline' or 'different'. The performance of the regression method and the model-based method was comparable. Both methods were preferable to the quasi-orthogonal method. The kappa values for the preferred methods indicated a good to excellent diagnostic agreement between the original and reconstructed VCGs. Only one out of ninety VCGs that were reconstructed with the regression method was classified as 'different' compared with the original VCGs; three VCGs were classified as 'different' with the model-based method. It was also found that estimation of similarity by a distance measure could not replace diagnostic evaluation by skilled observers.

Electrocardiography↗

PubMed1990

The Delphi method to validate diagnostic knowledge in computerized ECG interpretation.

We investigated the applicability of the Delphi method for increasing the agreement among multiple cardiologists on, firstly, their classifications of a set of electrocardiograms and, secondly, their reasons for these classifications. Five cardiologists were requested to judge the computer classifications of a set of thirty ECGs. If a cardiologist disagreed with the computer classification, he had to provide a new classification and a reason for this change. The results of this first round were compiled and anonymously fed back to the cardiologists. In a second round the cardiologists were asked once again to judge the ECGs and to rate the reasons provided in the first round. The level of agreement was estimated by means of the kappa statistic. The Delphi procedure substantially increased the agreement on the classifications among the cardiologists. The final agreement was very high and comparable with the intraobserver agreement. There was also a high level of agreement on the reasons provided by the cardiologists. However, their use in improving the program's performance is hampered by the qualitative nature of many of the reasons. Suggestions are given for a more formalized elicitation of knowledge.

Delphi Technique↗

PubMed1987

The contribution of afferent information on position and velocity to the control of slow and fast human forearm movements.

We applied vibration at various rates to the biceps tendon of a passive, restrained arm in normal human subjects and measured its effect on the perception of forearm position and the perception of forearm velocity. The disturbances of limb position perception and limb velocity perception depended on the vibration rate in distinctly different ways. We thereupon applied vibration at various rates to the biceps tendon during the performances of non-visually-guided slow and fast forearm movements. The vibration-rate-dependence of the disturbance of slow movements matched the vibration-rate-dependence of the disturbance of limb position perception. The vibration-rate-dependence of the disturbance of fast limb movements matched the vibration-rate-dependence of the disturbance of limb velocity perception. It is concluded that afferent position information is dominant in the control of slow movements, whereas mainly afferent velocity information is used in the control of fast movements.

Adult↗