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Biomedical subjects

G C Theodoridis

Publications and source records attributed to G C Theodoridis.

7 recordsLinked to original sources
PubMed1991

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.

Animals↗
PubMed1990

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.

Analysis of Variance↗
PubMed1988

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.

Attention↗
PubMed1985

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.

Adolescent↗