PubMed · 4261938
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A Martin, J L Thillier. 1971. [Electrogastroenterography (E.GE.G)].. https://pubmed.ncbi.nlm.nih.gov/4261938/
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Technical and instrumentation factors play an important role in obtaining reliable information during electrodiagnostic studies. With contemporary electrodiagnostic equipment, neurophysiologic potentials are detected using a variety of electrodes and undergo differential amplification, filtering, conversion to digital form, and finally, analysis and display. Understanding the signal processing principles, limitations, and sources of errors that can occur during this multistep process can improve the technical quality of studies, minimize preventable errors, and improve clinical interpretation. Part I of this minimonograph reviews the basic principles of action potential generation and overviews electrodiagnostic instrumentation. The concept of waveform frequency content is related to the role of filters in suppressing noise while preserving waveform latency, amplitude, and morphology. The electrical characteristics of various surface and needle electrodes influence instrument design and the nature of the potentials recorded. This is especially important in understanding the differences in motor unit characteristics obtained from monopolar and concentric needle electrodes.
We consider two approaches to the interpretation of EPG data, using materials designed for the investigation of [s]-[integral of] assimilations across word boundaries, as in boss Shep. A contact index is based on electrode contact in different row groups, whereas a neural network is used to determine patterns of contact. Both approaches are speaker sensitive, reflecting the wide variation in [s] and [integral of] articulation between speakers. The advantage of the neural net analysis is that the investigator need not make any assumptions about the relative value of specific electrodes or groups of electrodes. We found that the 'hand-selected' index, in general, modelled linguopalatal movement for all degrees of [s]-[integral of] assimilation better than the neural net. However, the neural net very successfully characterised stable /s/ and /integral of/ and has the potential to give an accurate representation of intermediate assimilatory cases, if trained on a more varied input set than the rather limited one used in this experiment.
A new method of electropalatographic (EPG) data reduction is proposed. It uses the so-called discrete cosine transform for representing an EPG pattern as a weighted sum of elementary 'pictures'. It is shown that several of these pictures can be considered as being articulatorily relevant. The respective contributions of these pictures to the spatial arrangement of the linguopalatal contacts are given by transform coefficients which are used here as a set of new EPG indices: the scaled sum of contacts index (SSU), the left-right asymmetry index (LRA), the alveolar-palatal index (APA) and the lateral-median index (LME). It is shown that the information extracted from an EPG pattern by means of these indices is maximised. Because of its robustness, this method could be usefully employed in studies on articulatory disorders.