Search

Purpose: Factor analysis is a useful technique to aid in organizing multivariate data characterizing speech, language, and auditory abilities. However, knowledge of the limitations of factor analysis is essential for proper interpretation of results. The present study used simulated test scores to illustrate some characteristics of factor analysis. Method: Linear models were used to simulate test scores that were determined by multiple latent variables. These simulated test scores were evaluated with principal components analysis and, in certain cases, structural equation modeling. In addition, a subset of simulated individuals characterized by poor test performance was examined. Results: The number of factors recovered and their identity do not necessarily correspond to the structure of the latent variables that generated the test scores. The first principal component may represent variance from multiple uncorrelated sources. Practices such as correction or control for general cognitive ability may produce misleading results. Conclusions: Inferences from the results of factor analysis should be primarily about the structure of test batteries rather than the structure of human mental abilities. Researchers and clinicians should consider multiple sources of evidence to evaluate hypotheses about the processes generating test results.

Discusses the difficulty in validating central auditory processing disorder (CAPD) as a diagnostic label in school-aged children, and examines the extent to which reading, language, and attention disorders in school-aged children involve perceptual dysfunctions limited to a single sensory modality. Multimodal perceptual testing for diagnosis is discussed. (Author/CR)

This paper examines the case for modality specificity as a criterion for improving the specificity of diagnosing central auditory processing disorders. Demonstrating the modality-specific nature of sensory processing deficits is seen as one way to rule out nonperceptual factors as explanations for observed dysfunction. (Author)

A brain-computer interface (BCI) is a system that provides an alternate nonmuscular communication/control channel for individuals with severe neuromuscular disabilities. With proper training, individuals can learn to modulate the amplitude of specific electroencephalographic (EEG) components (e.g., the 8-12 Hz [micro] rhythm and 18-26 Hz [beta] rhythm) over the sensorimotor cortex and use them to control a cursor on a computer screen. Conventional spectral techniques for monitoring the continuous amplitude fluctuations fail to capture essential amplitude/phase relationships of the [micro] and [beta] rhythms in a compact fashion and, therefore, are suboptimal. By extracting the characteristic [micro] rhythm for a user, the exact morphology can be characterized and exploited as a matched filter. A simple, parameterized model for the characteristic [micro] rhythm is proposed and its effectiveness as a matched filter is examined online for a one-dimensional cursor control task. The results suggest that amplitude/phase coupling exists between the [micro] and [beta] bands during event-related desynchronization, and that an appropriate matched filter can provide improved performance. Index Terms--Brain-computer interface, electroencephalogram, matched filter, sensorimotor rhythms, spectral analysis.

Many laboratories have begun to develop brain-computer interface (BCI) systems that provide communication and control capabilities to people with severe motor disabilities. Further progress and realization of practical applications depends on systematic evaluations and comparisons of different brain signals, recording methods, processing algorithms, output formats, and operating protocols. However, the typical BCI system is designed specifically for one particular BCI method and is, therefore, not suited to the systematic studies that are essential for continued progress. In response to this problem, we have developed a documented general-purpose BCI research and development platform called BCI2000. BCI2000 can incorporate alone or in combination any brain signals, signal processing methods, output devices, and operating protocols. This report is intended to describe to investigators, biomedical engineers, and computer scientists the concepts that the BCI2000 system is based upon and gives examples of successful BCI implementations using this system. To date, we have used BCI2000 to create BCI systems for a variety of brain signals, processing methods, and applications. The data show that these systems function well in online operation and that BCI2000 satisfies the stringent real-time requirements of BCI systems. By substantially reducing labor and cost, BCI2000 facilitates the implementation of different BCI systems and other psychophysiological experiments. It is available with full documentation and free of charge for research or educational purposes and is currently being used in a variety of studies by many research groups. Index Terms--Assistive devices, augmentative communication, brain-computer interface (BCI), ECoG, electroencephalography (EEG), psychophysiology, rehabilitation.

Thresholds for the discrimination of temporal order were determined for selected auditory and visual stimulus dimensions in 10 normal-adult volunteers. Auditory stimuli consisted of binary pure tones varying in frequency or sound pressure level, and visual stimuli consisted of binary geometric forms varying in size, orientation, or color. We determined the effect of psychophysical method and the reliability of performance across stimulus dimensions. Using a single-track adaptive procedure, Experiment 1 showed that temporal-order thresholds (TOTs) varied with stimulus dimension, being lowest for auditory frequency, intermediate for size, orientation, and auditory level, and longest for color. Test performance improved over sessions and the profile of thresholds across stimulus dimensions had a modest reliability. Experiment 2 used a double-interleaved adaptive procedure and TOTs were similarly ordered as in Experiment 1. However, TOTs were significantly lower for initially ascending versus descending tracks. With this method, the reliability of the profile across stimulus dimensions and tracks was relatively low. In Experiment 3, psychometric functions were obtained for each of the stimulus dimensions and thresholds were defined as the interpolated 70.7% correct point. The relative ordering of TOTs was similar to those obtained in the first two experiments. Non-monotonicities were found in some of the psychometric functions, with the most prominent being for the color dimension. A cross-experiment comparison of results demonstrates that TOTs and their reliability are significantly influenced by the psychophysical method. Taken together, these results support the notion that the temporal resolution of ordered stimuli involves perceptual mechanisms specific to a given sensory modality or submodality. KEY WORDS: temporal-order, sensory modality, central auditory processing

Distortion product otoacoustic emissions (DPOAEs) measured from the ear canal can be a sensitive tool to detect changes in cochlear function over time. However, if multiple-measurement procedures are to be useful clinically, testing needs to be reliable and sources of variability within individuals should be known. Herein, the influence of time-of-day (TOD), stimulus frequency, stimulus sound pressure level (SPL), and gender were evaluated on 2f1-f2 DPOAE amplitude in 16 adult volunteers with normal hearing. The effects of oral temperature and resting-pulse rate were also assessed. This study demonstrated a TOD main effect, with a period approximating one cycle-per-day. The magnitude of this effect averaged less than one dB and was not dependent on stimulus (frequency or SPL) or participant variables (gender, oral temperature, or resting-pulse rate), nor was it synchronized to a particular point-in-time. Stimulus level and gender effects on DPOAEs across frequency were also observed. Using generalizability theory (GT), DP iso-level/frequency profiles (DPILFPs) were found to be reliable measures within-subjects over a contiguous 24-hour time period. Significant and reliable between-subject differences were also documented. This study demonstrates the influence of stimulus and participant variables, quantifies the within-subject reliability over a 24-hour time period, and confirms that significant and reliable between-subject differences exist on DPOAEs across frequency, SPL, and gender. KEY WORDS: distortion product otoacoustic emissions, individual differences, reliability, gender effects, circadian rhythm