George C. Theodoridis

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.

Central role of solar information flow in pregenetic evolution

Abstract The accumulation of biospheric information during pregenetic evolution requires the presence of mechanisms linking the evolving structures to the biospheric information input. It is possible to visualize such accumulation of information within functional, non-reproducing structures through evolutionary mechanisms linking their information-related function to the probability of their disruption. Non-functional, self-reproducing structures cannot evolve and accumulate biospheric information, since they have no access to the biospheric information input. During pregenetic evolution biospheric information may have thus accumulated within functional, non-reproducing polypeptides rather than within non-functional, selfreproducing polynucleotides.

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 individuals 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.

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.

Analysis of epileptic activity in a system of interconnected neurons. A biological criticality theory.

In this theoretical study of epileptiform activity, the onset of self-sustained activity in a system of interconnected cells is explored using (a) analytical models, and (b) computer simulations. An approximate analytical model demonstrates that the system can be either stable, with self-sustained activity impossible, or potentially unstable, with the possibility of going into self-sustained activity if the firing rate is driven beyond a critical level. The approximations made in this initial model led to substantial discrepancies when the analytical criticality condition was tested against computer simulations in relatively small networks of neurons. Therefore, using a refined analytical model, a numerically more accurate, although computationally cumbersome, criticality condition was derived which agrees well with the simulation results. Two simulation models are used: a deterministic simulation in which the average number of cells firing at each simulation step is calculated and a probabilistic simulation in which the stimulation and firing of each individual neuron is followed. Comparison between the behavior of the probabilistic and deterministic simulations near criticality demonstrates that random fluctuations can force the system toward either self-sustained activity or decay.

Age distribution, education and societal structure

Abstract Age distribution, educational distribution and societal structure are interrelated parameters that, in the past, were adjusted to each other in an equilibrium that was only perturbed by rather small and slow changes. Built-in trial and error control mechanisms were evidently capable of containing these minor perturbations without excessive instabilities. Recently, major and fast changes have been occurring in the age distribution through the substantial extension of human life expectancy, and in the educational distribution through the wide availability of educational opportunities. The existing trial and error control mechanisms seem to be inadequate for such major perturbations, and new controls will have to be introduced in order to avoid serious instability and disruption. While the age distribution cannot be controlled through morally acceptable means, ways must be found to control the educational distribution, and to match it to existing societal needs.

On the physical role of motivational forces in the operation of the biosphere

Motivational forces are discussed within the context of the physical operation of the terrestrial biosphere as an information processing system. The main categories of needs and desires that motivate the actions of individual organisms can be understood within the concept of information maximization as the apparent operational objective and criterion of performance of the biospheric system. Motivational forces such as the urge for activity, the instinct for survival, as well as the needs that are aimed at genetic and cultural reproduction, can be quantitatively expressed in a common currency by translating them into the equivalent amounts of biospheric information that they are contributing.

Information and biotechnological systems

Abstract A biotechnological system can be described and analyzed in terms of the information that it processes and the information of which it consists. The quality and the operational efficiency of the system, inversely related to the amount of irreversibilities that it contains, are measured by the average lifetime of the processed information and by the informational content of the system. The development of new biotechnological systems is treated for specific cases, and the results are compared with data on the development of the telephone and the computer.

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.