A biologically inspired controller for hexapod walking: simple solutions by exploiting physical properties.

The locomotor system of slowly walking insects is well suited for coping with highly irregular terrain and therefore might represent a paragon for an artificial six-legged walking machine. Our investigations of the stick insect Carausius morosus indicate that these animals gain their adaptivity and flexibility mainly from the extremely decentralized organization of the control system that generates the leg movements. Neither the movement of a single leg nor the coordination of all six legs (i.e., the gait) appears to be centrally pre-programmed. Thus, instead of using a single, central controller with global knowledge, each leg appears to possess its own controller with only procedural knowledge for the generation of the leg's movement. This is possible because exploiting the physical properties avoids the need for complete information on the geometry of the system that would be a prerequisite for explicitly solving the problems. Hence, production of the gait is an emergent property of the whole system, in which each of the six single-leg controllers obeys a few simple and local rules in processing state-dependent information about its neighbors.

Simulation of complex movements using artificial neural networks.

A simulated network for controlling a six-legged, insect-like walking system is proposed. The network contains internal recurrent connections, but important recurrent connections utilize the loop through the environment. This approach leads to a subnet for controlling the three joints of a leg during its swing which is arguably the simplest possible solution. The task for the stance subnet appears more difficult because the movements of a larger and varying number of joints (9-18: three for each leg in stance) have to be controlled such that each leg contributes efficiently to support and propulsion and legs do not work at cross purposes. Already inherently non-linear, this task is further complicated by four factors: 1) the combination of legs in stance varies continuously. 2) during curve walking, legs must move at different speeds, 3) on compliant substrates, the speed of the individual legs may vary unpredictably, and 4) the geometry of the system may vary through growth and injury or due to non-rigid suspension of the joints. This task appears to require some kind of "motor intelligence". We show that an extremely decentralized, simple controller, based on a combination of negative and positive feedback at the joint level, copes with all these problems by exploiting the physical properties of the system.

A fast, three-layer neural network for path finding.

A path-planning algorithm is proposed to find a path based on local rules applied to a three-layer artificial neural network. Each layer consists of two-dimensionally arranged neurons with recurrent connections within a limited neighbourhood. The output of one layer determines the weights of the connections in the next layer. In principle, the method is based on a diffusion process, but is modified such that it does not suffer from several drawbacks involved in this algorithm. By application of a nonlinear transformation in layer 2, the diffusion front has the qualitative properties of a propagation wave. Therefore, limited resolution of the units is not critical, in contrast to classical diffusion algorithms. Furthermore, the algorithm generally does not suffer from the superposition of diffusion gradients when several paths are possible. The diffusion takes place in a space covered with 'obstacle potentials' which decrease the velocity of the diffusion front. In this way the path can maintain an adjustable safety margin in relation to the obstacles, for example, to cope with problems of incomplete knowledge of the obstacle's position. The algorithm thus combines the advantages of the diffusion algorithm, namely avoidance of local minima, of wave propagation, i.e. coping with limited resolution, and the potential field approach, i.e. maintaining a safety margin in relation to obstacles. The distributed architecture also allows for 'spatial interpolation' between the units (coarse coding), thereby providing smooth path forms. A comparison with paths developed by human subjects shows some similarity on the qualitative level, but there are also obvious differences.

[Comparison of results of daily blood pressure self-monitoring and general practice monitoring within the scope of a study assessing treatment of hypertension with quinapril]. / Vergleich der Ergebnisse von täglichen Blutdruckselbstmessungen und Praxismessungen im Rahmen einer Studie zur Behandlung der Hypertonie mit Quinapril (Accupro).

24 hour blood pressure monitoring is a well established method in the field of antihypertensive research. Patients self recorded blood pressure values are an additional option to overcome the disadvantages of casual office readings--however they are not frequently used within intervention trials. To prove the usefulness of selfrecordings in clinical trials we investigated both selfrecordings taken twice a day and casual readings within intervals of 1 to 3 weeks, in this study on the efficacy and tolerability of the ACE-inhibitor Accupro. 108 hypertensive patients (grade WHO I to II) were included in this trial for ten weeks. Although blood pressures were measured by the patients using sphygmomanometers of the same type and the physicians, decisions to treat or to increase dosage were based on the patients' recordings only. Accupro was dispensed according to the package leaflet at a daily dosage of 5 mg up to 40 mg. In case of failing response to monotherapy, Accupro was combined with Diltiazem or with a diuretic. 7 patients discontinued the treatment due to mild adverse events, one did not cooperate. 82 of the remaining patients were treated effectively with Accupro monotherapy--60 (73%) got one dose daily, 22 (27%) 2 doses per day,--and in 18 patients a drug combination was required. Therapeutic response (RRd < or = 90 mm Hg) was gained within 86 of the 100 evaluable patients according to the doctors' and 83 according to the patients' records. In this respect the two methods used gave comparable overall results. This somewhat surprising fact is due to the design of the study, because treatment decisions were based on the selfrecordings only. Clinical trials based on selfrecordings are in some points preferable to casual office readings: As patients being normotensive at home should not be included into an interventional study, a change of dosage within this group is avoided. Additionally the compliance of a cooperative patient taking his blood pressure twice daily is at a high level. Measurements of each single patient may be evaluated statistically by time series-analysis regarding longterm distribution of blood pressure-values. Taking the means of selfrecordings over adequate time-intervals eliminates the influence of "outliers" (occasionally extremely high or low values) and also reduces the standard deviation compared to that of the casual readings. Research work based on self recordings provides more information and therefore more security for treatment decisions.

Further observational data on the behavioral and social world of institutions for the aged.

This study is an extension of previous observational work on the social ecology of dependence and independence in the institutionalized elderly. Observations of everyday, naturally occurring interactions between elderly residents of two different long-term institutions and their social partners were extended such that, aside from the identification of type of behavior, the dyadic form and continuity of each behavior was specified. The following were among the major results: (a) Previously found interaction patterns between elderly residents and their social partners, replicated in both a nursing home and a home for the chronically ill, supported the notion of discrepant social ecologies for dependent versus independent behaviors of residents: (b) specification of each behavioral act as to its dyadic form underscored the fact that the interactions were controlled largely by social partners and not by the elderly residents; (c) coding continuity or discontinuity of behavior suggested that independent behaviors were maintained by chaining; and (d) elderly residents in the home for the chronically ill evinced, as expected, more dependence-related behaviors.

[Observation of dependent and independent behavior in a German old age home: the social environment as an influencing factor]. / Die Beobachtung von unselbständigem und selbständigem Verhalten in einem deutschen Altersheim: Die soziale Umwelt als Einflussgrösse.

The present study was an attempt to replicate observational data on dependence vs. independence obtained from American nursing home populations. For a period of three weeks naturally occurring interactions between 39 residents of a nursing home and their social partners were observed daily. The results of the replication study support the findings concerning the interaction patterns demonstrated in the American studies. Dependent behavior of residents in the context of self-care is followed most frequently by dependence-supportive behavior of social partners; independent self-care behavior as well as passive and destructively engaged behavior of residents is followed by "no response" of social partners, while constructively engaged behavior sometimes entails engagement-supportive behavior by social partners. As for the frequency distribution of the observed behavior there is both consistency as well as divergence between the American and Berlin data. These differences are partly the result of culturally linked differences in customs and administrative habits developed in the daily routine of an institution.