Browsing by Author "Troelstra, Arne"

Now showing 1 - 5 of 5
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    A preliminary evaluation of the human ERG obtained with sinusoidally varying light stimulation
    (1977) Dittert, Karen Kay; Troelstra, Arne
    This thesis evaluates the human ERG obtained with sinusoidally varying light stimulation. Eighteen test frequencies are used, varying from 2 to Hz. The test is administered to both normals and patients with retinitis pigmentosa (R.F.) The output waveforms are subjected to a Pourier analysis, and the Fourier coefficients form the data base for a cluster analysis. The clustering methods have three main goals: 1) To automatically separate the normals and the R.P.'s, based on the Pourier coefficients, 2) To find groups among the R.P.'s based on these coefficients, and 3) To investigate these groups for a relationship with physiological or clinical variables that the ophthamologist measures. Three methods of clustering are employed: 1) The K-Keans algorithm, 2) A hierarchical method, and 3) Approximation of the frequency versus phase of the first harmonic graph. Normals are grouped correctly by all methods, while all but three R.P. eyes are separated as abnormal. The greatest correlation occurs with the flash ERG. The phase approach leads to the most promising results, and further research in this area is suggested.
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    An analysis of a model of extraocular muscle cooperation
    (1978) Brzustowicz, Thomas Jude; Troelstra, Arne
    A model of the mechanics of human eye positioning has been evaluated for accuracy by comparison with clinical data of typical oculomotor diseases. By extending the existing monocular characterization to include interaction between a pair of eyes. a new binocular model is implemented. Furthermore. the improved iterative scheme developed for obtaining eye position from innervation of extraocular muscles insures convergence to a solution in only a few iterations. Computer programs implemented to solve this problem and its inverse are now coupled in such a way that the resulting model describes the innervational control and mechanics of positioning two eyes when one is fixating and the other is following under cover. Using this binocular model. an atlas of plots of hypothetical oculomotor defects and surgeries is compiled. Each plot simulates the prism-cover test and shows the normal left eye fixing at nine diagnostic positions and the corresponding locations of the following right eye. Abnormalities implemented for the covered eye include: a muscle palsy, a 5% weakened muscle, and a 5% strengthened muscle. In addition. surgical corrections such as myectomies, recessions, resections, and various combinations thereof are also simulated. Clinical data of 7 actual cases of oculomotor pathology are plotted in the same format as the hypothetical cases. The patient data are simulated in two different stages: First» the patient's condition both before and after surgery is simulated in accordance with a simple diagnosis. Recognizing that isolated defects rarely exist clinically, additional complications are then suggested. On the basis of hypothetical simulations in the atlas, changes in model parameters are made which yield prism-cover results more closely corresponding to the patient's pre-surgery data. Using this refined model, the simulations of surgical corrections are also improved. The results are treated in two separate cases: 1) the hypothetical cases* and 2) the clinical cases. The hypothetical results dealing with the four recti are in excellent agreement with accepted ideas. Although different from traditional views in some ways, the plots of the obliques appear reasonable. Similarly, the clinical cases show good agreement for the rectus muscles, while the obliques are not as well represented. An analysis of the results suggests that the model represents the general properties of the static extraocular system well and is a good starting place from which to develop a more accurate and sophisticated model. It is hoped that this thesis will benefit further work in this area.
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    Development of automatic sleep stage discrimination using Period Analyzed EEG
    (1977) Pruett, Roderick C.; Troelstra, Arne; Figueiredo, Rui J. P. de; Kazakos, T.; Burch, N. R.; Saltzberg, B.; Dossett, R.
    A sleep stage classification method has been developed which uses variables derived from the Period Analyzed EEG to discriminate seven stages of sleep with accuracies of 88-99%. Period Analysis is a method through which the vast EEG data base can be condensed to a relatively small number of highly informative values. These values are the numbers of zero-crossings per second of the signal and its first and second derivatives. Stepwise discriminant analysis was used to determine which of these variables to use, and to calculate coefficients for six classification functions, based on a learning set of visually classified EEG samples. To evaluate the performance of this method various learning and test sets from the same subject were used, obtaining agreements with the visual classifier of 96-99% on reclassifications of the night in the learning set, 9-94% on intra-night test sets, and 88-94% on test sets isolated from the learning set by a month. Stage REM was discriminated from the EEG without the use of EOG leads, along with Stages I-IV, Awake, and Artifact. These inter-night hit rates were much higher than others in the current literature, and even greater than published inter-judge or even intra-judge agreements when reclassifying the same samples -- indicating a sleep stage classification system which is both highly accurate and extremely precise.
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    Functional connections between motion detectors in the optic nerve and connective of the crayfish
    (1980) Martel, Michael Lee; Glantz, Raymon M.; Sass, Ronald L.; Troelstra, Arne
    Results are reported here from experiments in which single unit neural activity was recorded simultaneously from the optic nerve and connective of the crayfish Procombarus clarkli to study functional connections between units responding to movement in visual space. The single unit data was analyzed through computer generated plots of poststimulus time histograms, interspike interval histograms, autocorrelation plots, joint peristimulus time histograms and normal and shifted crosscorrelation plots. In three experiments, discussed here in detail, evidence was obtained for strong functional connections between optic nerve motion detectors and connective motion detectors. In two other experiments, evidence was obtained for strong functional connections between the connective motion detectors and units in the other two classes of crayfish optic nerve visual units: the sustaining units and the dimming units.
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    The use of strength-duration curves for system identification
    (1972) Foltz, James Monroe; Troelstra, Arne
    The inputs to systems which exhibit threshold behavior can be characterized by a strength-duration curve. In its most basic form, this curve gives the amplitude (strength) of an input required to exceed threshold as a function of the duration of that input. These curves have historically been used to identify physical characteristics of certain biological systems. E.g., in the nervous system, how are the position and shape of the curve related to nerve conduction velocity or membrane time constant; in the visual system, how are these characteristics of the curve related to rod and cone function, etc. In this thesis, methods of analysis are developed in an attempt to solve the more general problem of how the properties of a strength-duration curve for a general system, defined mathematically, relate to the parameters of that system. The approach used to gain insight into this problem is to investigate the effect of a change in a linear, time-invariant system on its strength-duration curve. Two system changes are considered: addition of a pole, and addition of a zero, to the transfer function. The effect of these changes on ^reai;, a parameter of the curve, is investigated. It is found that, in certain cases where rather severe restrictions are imposed on the system impulse response always increases with addition of a pole, and always decreases with addition of a zero. The special case of a system with transfer function is solved numerically. The impulse response of this system does not satisfy the severe restrictions mentioned above, but the results are the same, indicating that will shift in this manner when a pole or zero is added to the transfer function of any system. In an attempt to demonstrate the feasibility of the theoretical analysis, strength-duration curves are plotted from data taken from stimulating the frog sciatic nerve with rectangular voltage pulses. The experimental error involved in these plots is estimated. Two different experimental conditions produce curves with a significant difference, which can be explained by the above theoretical results. Since the strength-duration curve analysis discussed in this thesis is not unique, i.e., different linear, time-invariant systems may produce identical strength-duration curves, an experimental observation can be explained in more than one way.