Biomedical subjects
Publications and source records attributed to S S Hacisalihzade.
An interactive program package for the acquisition, analysis and plotting of human eye movements is introduced. It is shown that the programs described in this paper can be used by scientists in a wide range of disciplines in spite of their different data analysis requirements. An example dealing with smooth pursuit tracking is given.
A nonlinear model for the stretch reflex has recently been used to study the interactions between voluntary and reflex controls during fast, targeted movements. The present study explores the topography of a 'behaviour space' generated by computer simulations of this model under various combinations of values for the gain parameters and time constants in the model's feedback loops. In general, we define a behaviour space to be any set of behavioural characteristics of the simulated movement, such as movement time, peak acceleration or peak velocity. The mathematical model can therefore be viewed as an M x N dimensional map from its parameter space N to a behaviour space M. Here, a one-dimensional behaviour space is explored. This provides a method for quantitatively comparing the different control strategies that might be employed by the nervous system for integrating reflex and descending signals during fast, voluntary movements. The results indicate that an optimal strategy will employ proprioceptive feedback as a means of fine-tuning the braking and clamping activities of fast, goal-directed movements and that descending signals are primarily important for initiating the movement and for controlling reciprocal patterns of muscle activity during the end phase of the movement.
Smooth-pursuit eye-tracking dysfunction is a putative genetic trait marker for schizophrenia. In this study 88 Japanese schizophrenics from Kyushu and Okinawa were examined for the marker using precise high-resolution instrumentation: 76% of the schizophrenics from Kyushu and 89% of those from Okinawa had pursuit dysfunction. The presence of the culture-neutral smooth-pursuit marker for schizophrenia in Japan demonstrates that the etic concept "schizophrenia" is cross-culturally valid. Furthermore, the ubiquity of the marker in biologically and culturally diverse populations may indicate a limit on the extent of meaningful heterogeneity likely to be discovered within the condition.
The effects of VDT resolution on visual fatigue and readability were studied. Two kinds of displays with different resolutions (1664 x 1200 pixels and 720 x 350 pixels) and fonts were used. In the first experiment, the subjects read from each display for 1 h to induce fatigue. Reading speed and blink rate while reading were measured. Eye movements during visual smooth pursuit tracking tasks were studied before and after reading; quantitative scoring of eye movement performance showed no significant changes. In the second experiment, readability tests with three different character sizes on both displays were conducted and resulting reading eye movements were analysed. For readability of sufficiently large characters, no significant difference between the high and the standard VDT could be detected. However, for very small characters, higher resolution improved readability.
A third-order nonlinear mathematical model of the dose-effect relationship of levodopa, one of the most common drugs used for the symptomatic therapy of Parkinson's disease, is derived with the aid of a visual tracking based method which allows the measurement of some Parkinsonian symptoms quantitatively and objectively. The parameters of this model are identified for each subject separately due to the large interpatient variability in response to treatment. The model is then used to optimize the dosage regimen for each patient individually (according to the clinical particularities and needs of each patient) with respect to an objective function which includes the symptoms dynamically and the total amount of levodopa which is to be administered. Encouraging clinical results of this control engineering approach to therapy optimization are presented. The advantages and drawbacks of this approach are discussed and further research directions are indicated.
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The necessity of evaluating motor functions objectively and quantitatively is discussed. Tracking tasks and their appropriateness in assessing motor performance is reviewed. Motor performance can be effectively assessed by means of tracking tasks. A simple tracking device is presented which allows the measurement of motor performance in different conditions. It is pointed out that computers are well suited for driving the stimulus in tracking tasks as well as recording the performance in experiments based on tracking tasks. Differences between open and closed loop conditions, compensatory tracking, pursuit tracking, preview tracking and cognitive tracking are discussed. A flexible computer-controlled device is presented with which diverse experiments based on tracking tasks can be performed and their results recorded. A complete description of the user-oriented, interactive programs with which the experiments can be controlled and the relevant performance data can be recorded is given. An example of their application on measuring the effects of levodopa therapy on the motor symptoms of Parkinson's disease is presented.
A system theoretical approach to drug concentration-time data analysis is introduced after the discussion of some relevant concepts as they are used in system theory. The merits of this approach are demonstrated in multiple dosing problem. It is shown that dosage minimization without stringent constraints does not result in the desired therapeutic effect. In a different optimization the discrepancy between the actual and the desired time-histories of the relevant substance's plasma concentration is minimized. It is shown that both of these optimizations can be reduced to linear programming problems which are easily solvable with today's computers. These methods are demonstrated in a case study of dopaminergic substitution in Parkinson's disease where computer simulations show them to yield excellent results. Finally, the limits of this approach are also discussed.
A system theoretical approach to the general multiple dosing problem is discussed [1], which is in turn reduced to a classical parameter optimization problem. An efficient numerical algorithm based on the cyclic coordinate search method to solve the latter is explained. A flexible and user-friendly program written in standard FORTRAN which is suitable for this problem is introduced. Finally, the problem is applied to the dopaminergic substitution problem in Parkinson's disease, and the necessary input data as well as the resulting output is displayed in a sample run.
After a brief discussion of the existing methods of measuring various motor and other neurological functions as well as methods of inferring the parkinsonian symptoms therefrom, a simple computer based device and a method making use of pursuit tracking to assess different motor and neurologic characteristics are proposed. Computational methods of extracting attributes from the tracking data like the reaction time, the movement time and the error area between the reference signal and the tracking response are discussed. Measurements with a control population of healthy subjects are synopsized. Measurements with parkinsonian patients presenting tremor or bradykinesia as major symptoms are described. Finally, both results are compared.
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