Augmentative and alternative communication: exploring basic issues.

SUMMARY: An investigation of the effect of glottal source aperiodicities (jitter, shimmer, and aspiration noise) on the estimation of fundamental frequency (f0) perturbation and amplitude perturbation, of synthesized, glottal source and voiced speech waveforms, is considered. Firstly, 4, cycle-event f0 estimators are examined: (1) waveform matching of the low-pass filtered waveform, (2) positive peaks (PPs) from the speech waveform, (3) PPs from the low-pass filtered waveform, and (4) positive zero crossings from the low-pass filtered waveform. The analysis shows that f0 perturbation measures taken from the low-pass filtered waveform are affected by both amplitude perturbation and random glottal noise, whereas, f0 perturbation measures taken from the PPs of the original waveform are affected by noise but not by amplitude perturbation. It is shown for the low-pass filter methods that the effects of amplitude perturbation and noise lead to increased errors in the measurement of f0 perturbation for the synthesized speech waveforms when compared with the synthesized glottal waveforms. Shimmer of the synthesized speech waveform is approximately equal to shimmer of the synthesized glottal source. However, noise and jitter affect measures of amplitude perturbation. The estimation of f0 perturbation from the synthesized speech waveform is shown to be nonlinearly related to f0 perturbation estimation from the synthesized glottal waveform as a consequence of the filtering action of the vocal tract. Low-pass filtering the voiced speech waveform is shown to provide a partial solution to this problem.

Communication Devices for People with Disabilities↗

PubMed2006

Issues in AAC research: how much do we really understand?

PURPOSE: The purpose of this introductory paper is to provide some overview of and background to the issues that were raised at the Augmentative and Alternative Research Seminar in conjunction with the First Regional AAC conference on 23 February 2004. A group of 45 AAC researchers and professionals convened for one day to discuss some basic research issues in AAC. This paper highlights themes and perspectives that emerged from the research seminar discussions. METHOD: Literature reviews and discussion are used to provide a historical perspective on some of the issues raised. Two focus areas were identified for the purpose of this introductory paper; firstly, terminological issues that arose and secondly common themes that emerged during the paper presentations, discussions and/or written papers. Terminological issues include a brief description of the field of AAC for the benefit of those readers who might not be familiar with the field, whereafter the discussion focuses on the use of the term "complex communication needs" as referring to individuals who use AAC, the differentiation between symbols, signs, symbols sets and systems as well as the terms verbal and nonverbal, pre-linguistic and non-symbolic. The common themes throughout the papers include a discussion on the importance of context in communication, the chicken and egg question (i.e., comprehension and production), issues on multimodality, descriptive strategies for understanding interaction, and the use of typical interaction as a framework for understanding AAC interaction. CONCLUSIONS: In reviewing some of the issues in the field it is apparent that the issues we face now and those faced in AAC during earlier years are similar, however the need for a stronger database is apparent as the approach towards evidence-based practice becomes more prominent. The move to understand the nature of complex relationships in interaction is highlighted, for example, the multiple associations between environment, comprehension as well as the use of multi-modal communication. Whilst it became evident that most of these issues need further research in relation to typical interactions, applications to the field of AAC are most challenging.

Communication Devices for People with Disabilities↗

PubMed2006

Motor imagery and EEG-based control of spelling devices and neuroprostheses.

A brain-computer interface (BCI) transforms signals originating from the human brain into commands that can control devices or applications. With this, a BCI provides a new non-muscular communication channel, which can be used to assist patients who have highly compromised motor functions. The Graz-BCI uses motor imagery and associated oscillatory EEG signals from the sensorimotor cortex for device control. As a result of research in the past 15 years, the classification of ERD/ERS patterns in single EEG trials during motor execution and motor imagery forms the basis of this sensorimotor-rhythm controlled BCI. The major frequency bands of cortical oscillations considered here are the 8-13 and 15-30 Hz bands. This chapter describes the basic methods used in Graz-BCI research and outlines possible clinical applications.

Communication Devices for People with Disabilities↗