On selection mechanisms during initial evolution and on the possible role of ionic balance.

Initial evolution at the molecular level can proceed through mechanisms that enhance either the generation or the survival of certain molecules. Phenomena related to ionic balance can be the basis for both generative and survival selection mechanisms that may have driven the initial evolution of macromolecules. An important advantage of mechanisms based on ionic balance phenomena is that they can conceivably generate spatial and temporal inhomogeneities in semi-enclosed spaces within cavities of porous materials and/or membranes. Under certain circumstances, such inhomogeneities are required for initial evolution to proceed.

On evolutive systems and the initial evolution of structure and function.

As an instrument for the study of the early stages of evolution, we introduce evolutive systems, defined as systems that have the capacity to evolve given appropriate conditions in their environment. They consist of building blocks (e.g. monomers) that are either stable or in steady supply, and of transient assemblies (e.g. polymers) that are entities of great variety, some of which are capable of function. Evolution leads to the accumulation of structure within the transient assemblies during repeated cycles of disintegration (partial or total) and reassembly, on account of the selective advantages associated with transient assembly functions. Transient assemblies must be either inherently unstable or subject to disintegration by agents in their environment. Evolutive systems must have access to a negentropy input in the form of energy in packets larger than typical thermal energies. Reproduction, although not a prerequisite, greatly affects the capacity of evolutive systems to evolve, and thus can be expected to appear in an evolutive system if at all possible. Similarly, functions that require the expenditure of negentropy (for example mobility, breathing, circulation, sensing, communicating, etc.) are not prerequisites for evolution, but can be expected to become established in evolutive systems during evolution through the selective advantages that they confer. A computer-based evolutive automaton is used to explore possible evolutionary scenarios. In the presence of spatial and temporal inhomogeneities, one can construct a multitude of evolutionary scenarios through which various functions, such as the operation of genetic code, can become established within the evolutive automaton. This variety of possible evolutionary scenarios is all the more remarkable because the automaton does not include many important physical processes that would be present in a real system and would greatly multiply the number of possible evolutionary mechanisms and scenarios. Some evolutionary mechanisms are based on survival related selection, while others are based on generation related selection. Previously explored scenarios for the initiation of life have been based mostly on generation related selection. In this paper, we give particular emphasis to survival related selection which is more general in that it does apply to structures and functions related to reproduction but, unlike generation related selection, it is not limited to them. Some of the most basic features of terrestrial living systems can be seen either as prerequisite features of an evolutive system (such as the mortality of living organisms, instability of biological polymers, imperfect reproduction caused by mutations, and the need for a negentropy input) or as features that one can reasonably expect to become established in an evolutive system (such as reproduction and the multitude of living functions that require expenditure of negentropy). This suggests the possibility that an independent definition of living systems may not be necessary if features of living systems substantially overlap with features that one may expect to find in evolutive systems.

Memory effects to be considered in the design of measurements of the influence of context on speech perception.

One of the experimental parameters needed for the design of testing procedures for measuring context utilization in speech perception is the magnitude of memory effects. Such memory effects were studied using data obtained from normal-hearing subjects in experiments during which test words were presented under noise either in isolation or in the context of sentences. Each test word was presented twice; during each presentation the subject heard the test word several (five or six) different times, under progressively higher signal-to-noise (S/N) ratios. When the second presentation of a test word occurred during the same 1 h session as the first presentation, the observed memory effect was very large, being equivalent to a shift in S/N ratio of the order of 5 dB. In experiments during which the second presentation of a test word occurred after an interval of several days following the first presentation, the observed memory effect was equivalent to a shift in S/N ratio of the order of 1 dB.

Blood volume change and redistribution after change in posture.

A computational method developed by LaForte et al., 1992, and Lee, 1994, uses changes in hematocrit, plasma protein concentration, plasma density, or blood density to calculate the fluid restitution from the tissues to the blood, as well as the volume shift from micro- to macrocirculation; this microvascular volume shift is not taken into account by the preexisting methods for computing fluid shifts between the tissues and the blood based on changes in hematocrit. The new computational method was applied to published data obtained in two studies of posture change in humans by Hagan et al., 1978, and by Hinghofer-Szalkay and Moser, 1986. The results support the hypothesis that the microvasculature has the capacity to dilate or constrict so as to absorb a large part of the change in the total blood volume induced by posture change, thus ensuring minimal change in the filling of the macrocirculation.

The thalamocortical contribution to epilepsy.

The experimental literature has dealt intensively with the cortical contribution to epilepsy. Possibly because of the direction of technological advance, much less attention has been paid to the role of other structures. A model which emphasizes the role of some of those non-cortical structures, specifically that of thalamocortical modulation of cortical excitability, is developed. Some aspects of the petit mal seizure, a seizure type considered by some investigators to involve thalamocortical mechanisms, are predicted by the model. Although the thalamocortical mechanisms under study are not the only mechanisms underlying seizures, a full understanding of the phenomenology of epilepsy needs to take into account the role of subcortical modification of cortical activities in addition to other mechanisms. Gloor has described two types of epileptogenesis: type I characteristic of non-convulsive seizures and type II characteristics of convulsions. There is disagreement as to whether or not the two mechanisms represent qualitatively different phenomena. Utilizing the thalamocortical model, it can be shown that the two types of epileptogenesis are qualitatively different. Furthermore, the thalamocortical model leads to a possible explanation of clinically different profiles of antiepileptic efficacy of medications.

Procedure learning effects in speech perception tests.

The effects of procedure learning were studied using data obtained from normal-hearing subjects by presenting words under noise either in isolation or in the context of sentences. The data establish firmly an effect of procedure learning on the performance of subjects during a 1-hour testing session when the subjects have participated in a previous 1-hour testing session during which about 250 test words were presented. The magnitude of the effect is equivalent to a shift in signal-to-noise ratio of the order of 1 dB.

Comparison of various modes of presenting sentence materials in tests of speech perception in noise.

This study compares alternative modes of presenting sentences in testing situations where noise is employed and where the required response is only one word in the sentence. The purpose is to establish the extent to which contextual information is transmitted to the listener in the following four presentation modes: (1) acoustical presentation of the test word under noise and written presentation of the rest of the sentence (mode W); (2) acoustical presentation of sentence and test word under uniform noise (mode A); (3) superposition of the previous two modes (mode B); and (4) acoustical presentation of the test word under noise in one ear, immediately following the presentation of the rest of the sentence without noise in the other ear (mode C). Modes B and C are found to be essentially equivalent to mode W. When mode A is used, the intelligibility of the test word is substantially lower than with mode W, especially at low signal-to-noise (S/N) ratios. These results are particularly relevant to testing situations where the primary intent is to assess the utilization of contextual information in perceiving speech.

Measuring the contribution of printed context information to acoustical word recognition by normal subjects.

The present study focuses on measuring the contribution of context in the form of visually presented printed sentences toward the acoustical identification of a word. The results obtained demonstrate the feasibility of the objective selection and calibration of sentence material that could serve to quantify an individual's efficiency in utilizing contextual information during speech perception. In the employed experimental procedure, a reference group of normal-hearing subjects are presented acoustically with test words either in isolation or together with context in the form of a written sentence. The test words are presented under various levels of superimposed noise and the median signal-to-noise ratio at which identification occurs in the reference group serves to characterize the intelligibility of a particular presentation of a word or word-sentence combination. This median value is shifted toward lower signal-to-noise ratios when contextual information in the form of a sentence is provided along with the test word. The resultant context-induced shift can be adopted as an objective and quantitative measure of the effect of contextual information provided by the written sentence on the intelligibility of the test word. The data obtained in this study demonstrate that such context-induced shifts are large enough to be easily measured with the adopted experimental approach.

Decision analytic approach to the management of gonorrhea contacts.

We used a combination of decision analytic and modeling techniques in constructing a model for study of the management of an asymptomatic woman presenting to a sexually transmitted disease clinic as a contact of a man with gonorrhea. Total cost (physical, emotional, and economic) is expressed in units of dysutility. Initially the probabilities and "costs" of anogenital gonorrhea, incubating syphilis, carriage of the agents of nongonococcal urethritis, and coincident pharyngeal gonorrhea are considered; complications and sequelae are then accounted for. The best strategy is to culture for Neisseria gonorrhoeae, treat immediately with tetracycline, and follow up sexual partners if the culture is positive. Dysutility values calculated for the strategies of just treating with standard regimens of tetracycline, procaine penicillin, or amoxicillin are 288, 310, and 560, respectively. Sensitivity analyses show that the most important factors in determining optimal strategy are the probabilities and costs associated with the patient's carriage of the agents of nongonococcal urethritis. In order for this decision to change, the dysutility value for nongonococcal urethritis would have to decrease to 17% of our best estimate, or the overall prevalence of nongonococcal urethritis would have to be reduced to 16% of our best estimate.