Chromatic specificity of the visual evoked response.

The temporal alternation of red and green stripes in a structured field produces successive contrast, which can elicit cortical potentials recorded from the scalp. Amplitudes of the major frequency components of the potentials correspond to the relative intensities of red and green producing the contrast. The amplitude variations are color-specific, since total luminance and structure are held constant.

Brain potentials during sentence verification: late negativity and long-term memory strength.

Subjects decided whether self-referential statements were true or false. Event-related potentials (ERPs) associated with final words creating false statements displayed a late negativity (N340) relative to ERPs for true completions. The size of this difference between true and false statements was greater for highly familiar statements (e.g. "My name is Ira") than for less familiar ones (e.g. "I go to bed late") even after all the statements had been practised a number of times. The late negativity appears to be associated with a discrepancy between presented and remembered information, and its magnitude reflects the long-term familiarity or strength of the remembered information.

A critical review of electroglottography.

The technique of electroglottography is reviewed from the perspective of a laboratory instrument for assessing laryngeal function, a device to assist speech and speaker recognition, and as a potential diagnostic aid in the clinic. A description of the electronic functioning of the electroglottograph (EGG) is provided. Considerable emphasis is given to contemporary research which has focused on laryngeal assessment using the EGG. Methods for validating and aiding the interpretation or reading of the EGG are discussed, including photoglottography, stroboscopy, ultrahigh-speed laryngeal cinematography, and others. The relationship of the EGG to glottal area and glottal volume velocity estimated by inverse filtering is presented. An elementary model of the EGG is described and used to predict characteristic features of the EGG waveform. Clinical data as well as data obtained from subjects with a normal functioning larynx are analyzed. Applications of the EGG to speech processing are outlined, including real-time detection of voicing, voiced and unvoiced speech segments, and silence intervals. The EGG device has potential for assisting speech and speaker recognition systems in certain applications.

Event-related potentials: a critical review of methods for single-trial detection.

The analysis of ERP data has followed several lines over the last 20 years. The most prevalent method is simply to average ERPs for a given class of stimuli. The ERPs are compared for differences across classes of stimuli. Little other special data processing is used. The ERP comparisons are usually performed using visual examination of the wave-shapes. Sometimes statistics are calculated such as means, variances, and confidence limits. Linear filtering is used to reduce interference. Another approach is to model or analyze the ERP as a sequence of vectors or frames of data samples. These samples may be of the ERP time waveform or they may be of the frequency transform of the ERP waveform. The frames of data vary in length from the entire ERP waveform (500 to 1000 msec) to frames as short as ten sample points (100 msec). Recognition of an event in the ERP is achieved by computing a distance measure between parameter vectors for one class of stimuli and corresponding parameter vectors for another class of stimuli. Recognition is achieved by selecting the ERP with the lowest distance score. This approach is "pattern matching" and relies on two assumptions: adjacent frames of data are uncorrelated, and the variability of the data can be accounted for by the distance measured for all stimuli in the classes presented. Subject variability is generally not accounted for, other than to assume it is the same for all classes of stimuli. The data are clustered into a variety of reference patterns that represent particular manifestations of a particular stimulus. Another approach is "feature-based" recognition. The idea is to identify and automatically extract features of the data that can provide a characterization of stimuli. The features selected may be abstract. They are calculated from the data or transforms of the data.

Brain potentials during sentence verification: automatic aspects of comprehension.

College students learned a set of facts relating fictitious people and their occupations (e.g. 'Matthew is a lawyer'). Event-related brain potentials (ERPs) were recorded while they subsequently viewed a series of such statements presented in segments (e.g. 'Matthew/is a/dentist'). ERPs to occupations completing statements falsely were significantly more negative than those to true statements in an interval 200-420 msec poststimulus (peak N320), whether subjects were required to make a decision about each statement or passively view the presented segments (Experiments 1 and 2). A later ERP positivity was observed during 'response' trials that was of longer latency for false than true completions; but this positive component was greatly attenuated during 'no-response' trials. The enhanced N320 for false completions was not affected by requiring subjects on some trials to respond incorrectly (Experiment 3). It is concluded that attending to a presented word results in an automatic analysis of its meaning in the context of a preceding verbal input, and that ERPs can indicate the nature of the output of that analysis.

Measuring and modeling vocal source-tract interaction.

The quality of synthetic speech is affected by two factors: intelligibility and naturalness. At present, synthesized speech may be highly intelligible, but often sounds unnatural. Speech intelligibility depends on the synthesizer's ability to reproduce the formants, the formant bandwidths, and formant transitions, whereas speech naturalness is thought to depend on the excitation waveform characteristics for voiced and unvoiced sounds. Voiced sounds may be generated by a quasiperiodic train of glottal pulses of specified shape exciting the vocal tract filter. It is generally assumed that the glottal source and the vocal tract filter are linearly separable and do not interact. However, this assumption is often not valid, since it has been observed that appreciable source-tract interaction can occur in natural speech. Previous experiments in speech synthesis have demonstrated that the naturalness of synthetic speech does improve when source-tract interaction is simulated in the synthesis process. The purpose of this paper is two-fold: 1) to present an algorithm for automatically measuring source-tract interaction for voiced speech, and 2) to present a simple speech production model that incorporates source-tract interaction into the glottal source model. This glottal source model controls: 1) the skewness of the glottal pulse, and 2) the amount of the first formant ripple superimposed on the glottal pulse. A major application of the results of this paper is the modeling of vocal disorders.

Detection of laryngeal function using speech and electroglottographic data.

The purpose of this research was to develop quantitative measures for the assessment of laryngeal function using speech and electroglottographic (EGG) data. We developed two procedures for the detection of laryngeal pathology: 1) a spectral distortion measure using pitch synchronous and asynchronous methods with linear predictive coding (LPC) vectors and vector quantization (VQ) and 2) analysis of the EGG signal using time interval and amplitude difference measures. The VQ procedure was conjectured to offer the possibility of circumventing the need to estimate the glottal volume velocity wave-form by inverse filtering techniques. The EGG procedure was to evaluate data that was "nearly" a direct measure of vocal fold vibratory motion and thus was conjectured to offer the potential for providing an excellent assessment of laryngeal function. A threshold based procedure gave 75.9 and 69.0% probability of pathological detection using procedures 1) and 2), respectively, for 29 patients with pathological voices and 52 normal subjects. The false alarm probability was 9.6% for the normal subjects.

Brain potentials related to seeing one's own name.

Subjects were assigned an assumed name and then shown a series of statements of the form, "My name / is / X", where X was the assumed name, their own first name, or one of a set of other false names. Their task was to respond positively to the "assumed" name and reject as false all other names, including their own. An N380 feature of the averaged task-related brain potentials, considered to be inversely related to the degree of contextual priming, was greatly enhanced for the false names compared to the assumed name. The N380 to one's own name was more similar to that of the false than the assumed name, indicating that the sentence context's priming of various names was under the subjects' attentional control, and that the late negativity could be modulated by this attention. In contrast, a large P510 feature distinguished one's own name from the false name, and this difference was unaffected by practice. Even in cases, then, where the context allows anticipation of one verbal event (here, the assumed name), a highly overlearned and salient stimulus such as one's own name continues to produce a distinctive neural response.

Speech processing and synthesis for assessing vocal disorders.

Techniques for the quantitative assessment and classification of vocal disorders are described. Models for vocal disorders using speech synthesis are examined. Methods for characterizing the electroglottography (EGG) waveform and the assessment of vocal quality using acoustic and EGG signal features are discussed.