Cecil Thomas

• PhD, University of Texas
• Professor at Saint Louis University

The coherence function provides a measure of spectral similarity of two signals, but measurement noise decreases the values of measured coherence. When the two signals are the input and output of a linear system, any system noise also decreases the measured coherence values. In digital computations, useful coherence values require some degree of av...

In recorded bioelectric signals, such as the electrocardiogram, sinusoidal interference from power lines or other sources causes distortion in the signal and may lead to misdiagnosis. For long or continuous recordings, adaptive filtering can be effective in minimizing the interference. For short recording, the options are limited. Subtractive metho...

In 1971, Nicaragua issued ten stamps commemorating the "ten most important mathematical formulas". The back side of each stamp has a short text describing the equation and its utility. The stamps were a gift from Tim Klitz who is now a professor in the Psychology Department at Washington & Jefferson College. I have arranged the stamps in chronologi...

Studies investigating the effect of power frequency (50-60 Hz) electromagnetic fields (EMF) on melatonin synthesis in rats have been inconsistent with several showing suppression of melatonin synthesis, others showing no effect and a few actually demonstrating small increases. Scant research has focused on the ensuing sleep patterns of EMF exposed...

Multiple forms of a symbol-digit substitution task were used to provide a componential analysis of age differences in coding task performance. The results demonstrated age differences in feature encoding, memory, and visual search. A 2nd experiment was conducted with young adults to investigate a sensory deficit as a locus of age differences. The s...

The oral word reading speed of patients with Alzheimer's disease (AD) and healthy young and older control participants was evaluated across a broad range of stimulus contrast levels in two experiments. The impact of stimulus repetition on reading speed also was examined. It was found that the older adult participants, and particularly the AD patien...

Young and older adults were tested in both a letter-identification and a letter-matching task in which the integrity of the letter stimuli was manipulated through contrast reduction and low-pass spatial frequency filtering. The use of the contrast and filtering manipulations was an attempt to increase encoding difficulty in an effort to examine whe...

Young and older adults were tested in both a letter-identification and a letter-matching task in which the integrity of the letter stimuli was manipulated through contrast reduction and low-pass spatial frequency filtering. The use of the contrast and filtering manipulations was an attempt to increase encoding difficulty in an effort to examine whe...

Analysis and classification of sleep stages is a fundamental part of basic sleep research. Rat sleep stages are scored based on electrophysiological signals normally recorded from electrodes implanted epidurally and in the temporalis muscle. The process of scoring has generally been a labor and time intensive procedure involving the manual analysis...

We developed an adaptive forced-choice method whereby reference and test presentations were alternated in order to minimize effects from variables such as subject attention level. In our demonstration example of an X-ray fluoroscopy perception study, we measured detectability of low-contrast objects in noisy image sequences and determined X-ray dos...

A linear shift invariant system model describing coherent light-specimen interactions in optical coherence tomography is presented. Based on this model, an iterative deconvolution algorithm is demonstrated for enhancing the sharpness of optical coherence tomographic images of biological structures

1. Measurements were made in four normal human subjects of the accuracy of saccades to remembered locations of targets that were flashed on a 20 x 30 deg random dot display that was either stationary or moving horizontally and sinusoidally at +/-9 deg at 0.3 Hz. During the interval between the target flash and the memory-guided saccade, the "memory...

Video-based eye-tracking systems are especially suited to studying eye movements during naturally occurring activities such as locomotion, but eye velocity records suffer from broad band noise that is not amenable to conventional filtering methods. We evaluated the effectiveness of combined median and moving-average filters by comparing prefiltered...

Examined the hypothesis that the reading speed deficit often experienced by Alzheimer's disease (AD) patients could be modified through contrast enhancement. 10 AD patients (mean age 71.5 yrs), 10 nondemented elderly (mean age 67.1 yrs), and 10 young adults (mean age 18.8 yrs) were asked to identify briefly presented letters. The stimuli were shown...

Video-based eye-tracking systems are especially suited to studying eye movements during naturally occurring activities such as locomotion, but eye velocity records suffer from broad band noise that is not amenable to conventional filtering methods. We evaluated the effectiveness of combined median and moving-average filters by comparing prefiltered...

We compared ocular and eye-head tracking responses to an illusion of diagonal motion produced when vertical movement of a small visual target was synchronized to horizontal movement of a background display. In response to sinusoidal movement, smooth ocular pursuit followed vertical target motion, with only a small horizontal component. In response...

1. Humans may visually track a moving object either when they are stationary or in motion. To investigate visual-vestibular interaction during both conditions, we compared horizontal smooth pursuit (SP) and active combined eye-head tracking (CEHT) of a target moving sinusoidally at 0.4 Hz in four normal subjects while the subjects were either stati...

Pulsed fluoroscopy at reduced frame rates can be used to lower x-ray dose with equivalent detection (hereafter called equivalent perception) of low-contrast, stationary objects. Experimentally average dose savings of 22%, 38%, and 49%, for pulsed fluoroscopy at 15, 10, and 7.5 acquisitions per second, respectively, are documented. Dose savings depe...

Pulsed fluoroscopy (hereafter called pulsed) at reduced acquisition rates, typically 15 acq/s (pulsed‐15), is proposed to reduce x‐ray dose in interventional procedures. However, since the human visual system (HVS) acts as a temporal low‐pass filter that interacts with such acquisitions, the proper dose for pulsed must be obtained in perception exp...

Eight models are examined as input-output representations of steady-state vision in humans at moderate to low level illumination. Three new models for visual contrast sensitivity are introduced and evaluated using contrast sensitivity function (CSF) data with samples on both narrow and wide frequency ranges. Additionally, five variations of previou...

Patients with coarctation of the aorta (CoA) who previously underwent successful surgery are often diagnosed on standard electrocardiograms as having partial right bundle branch block. After surgery 24 patients with CoA had body surface potential mapping (BSPM) with the Case Western Reserve University 180 electrode system; of these 7 had additional...

Authors used a modeling approach to test the hypothesis that, in humans, the Smooth Pursuit (SP) system provides the primary signal for canceling the Vestibuloocular Reflex (VOR) during Combined Eye-Head Tracking (CEHT) of a target moving smoothly in the horizontal plane. Separate models for SP and the VOR were developed. The optimal values of para...

X-ray fluoroscopy is a significant source of x-ray dose to patients and hospital staff. One technique proposed for reducing dose is pulsed fluoroscopy at reduced frame rates, typically 15 frames/sec for cardiac angiography. Because the human visual system acts as a temporal low-pass filter, simply reducing the frame rate may not allow a dose reduct...

Without Abstract

Using the magnetic search coil technique, we measured torsional eye movements in four male subjects during and after rotation of a visual display around the line of sight. During rotation of the display, subjects developed a torsional nystagmus with slow-phases in the direction of target rotation that had a typical gain of less than 0.01. Upon cess...

We describe a procedure for modifying horizontal eye movement measurements in a way that effectively removes signal contributions due to the eccentric location of the eyes relative to the center of rotation of the head. This procedure helps standardize measured signals so that data collected under different experimental conditions and from differen...

Without Abstract

A reliable, noninvasive procedure to determine the location of accessory atrioventricular connections in patients with Wolff-Parkinson-White syndrome would add an important diagnostic tool to the clinical armamentarium. Body surface potential mapping (BSPM) using 180 electrodes in various-sized vests and displayed as a calibrated color map was used...

A new automatic spatiotemporal algorithm has been developed for detecting QRS onset and offset in body surface potential mapping. The new algorithm, based on a spatial and temporal approach, along with three other algorithms (total energy, 3-lead, and median), was tested in 73 normal and abnormal patients. The reference or gold standard onset and o...

A statistical classification method is suggested for body surface potential maps (BSPM). The initial data reduction utilizes the Fourier expansion and time integration, resulting in physiological-oriented features. Based on Fischer's criterion, optimal discriminant vectors are used to map the features to an optimal subdomain. Experimental criteria...

MULTIPLEXING STUDIES DURING ENTRAINMENT AND INTERRUPTION OF ATRIAL FLUTTER TO CHARACTERIZE DOUBLE POTENTIALS Akibiko Shimizu. MD. Akita Nozakl. MD, Cecil W. Thomas. PhD. Yoram Rudy. PhD. Albert L. Waldo. MD, FACC, Case Western Reserve University, Cleveland, OH. The center of the atrial flutter (AFl) reentry circuit in our sterile pericarditis cani...

Stylized chromosome images 1) serve as a format to test effects of preprocessing algorithms used in automated karyo-typing; 2) enhance the ability of humans to perform quantitative analysis of chromosomal aberrations; 3) provide an alternative format for karyotype hard copies produced by automated systems. Stylized chromosomes are two-dimensional c...

The authors address the problem of high-resolution inversion of finite Fourier transform data, which is frequently encountered in tomographic image reconstruction. A new parametric modelling approach, which uses an adaptive localised polynomial approximation model of the object function, is proposed to overcome the Gibbs artifact and the limited-re...

For pt.I see ibid., p.204-5, 1989. An interactive cardiac mapping system is described which integrates human intelligence and the power of computers. In pt.I the data acquisition hardware and software of this mapping system were described. After acquiring cardiac potential data, the next step is to analyze the data to obtain the activation sequence...

For pt.II see ibid., p.206-7, 1989. An interactive cardiac mapping system has been designed and implemented for recording from patients or animals. The data acquisition hardware and data acquisition software are described. The hardware consists of 240 monopolar cardiac amplifiers and a data processing system. The software provides an interactive en...

Spectral analysis to cardiac cycle length variations is discussed, and an inherent problem in nonuniformity of sample spacing is indicated. This nonuniformity can cause significant amounts of energy to be moved from the proper frequency into neighboring sidelobes. Resampling in the time domain prevents the energy redistribution in the frequency dom...

The authors present electrocardiographic body surface potential maps (BSPMs) of 11 patients with hypoplastic right ventricle (HRV) of three types: type I, HRV with pulmonary atresia; type II, HRV with tricuspid atresia; and type III, HRV with tricuspid artesia and transposition of the great arteries. The BSPMs of all 11 patients demonstrated eviden...

The technical aspects of a multiple-purpose cardiac mapping system are presented. The authors begin with a brief history of hardware and software development and then concentrate on the major problems in acquiring high-quality recordings from the torso surface or from the epicardial surface and on the processing of the signals for display of color...

Body surface potential mapping (BSPM) techniques have improved diagnosis of ischemia patients with normal resting ECG. The authors report BSPM data from 32 normal and 24 ischemia patients (all adults). The studies included: (1) separability of normal and ischemia from QRS integral maps (represented by normalized K-L expansion) by a two-layer forwar...