Philip Loizou

High vagal tone is associated with more efficient regulation of homeostasis in low‐risk human fetuses

Homeostasis is maintained primarily by the parasympathetic nervous system and is thought to provide a physiological substrate for the development of complex behaviors. This investigation was undertaken to test the hypothesis that infants with high parasympathetic tone are more efficient regulators of homeostasis than infants with low parasympathetic tone. Respiratory sinus arrhythmia (RSA) was used as a measure of parasympathetic tone, and the efficiency of homeostatic control was quantified, for each infant, by the slope (SRSA) and correlation coefficient (RRSA) of the regression line relating fluctuations in heart period and fluctuations in RSA. To test our hypothesis, we examined the relationship between RSA and both SRSA and RRSA in 34 low-risk human fetuses between 36 and 40 weeks gestation. We found that fetuses who were parasympathetic-dominated had larger SRSA and RRSA values, and hence were more efficient regulators of homeostasis, than fetuses who were sympathetic-dominated. The results of our analyses are important because they establish, very early in development, a physiological basis for the relationship between vagal tone and the development of complex behaviors.

A PDA-based Research Platform for Cochlear Implants

Currently researchers interested in developing new signal processing algorithms for commercially available cochlear implants must rely on coding these algorithms in low-level assembly language. We propose a personal digital assistant (PDA) based research platform for developing and testing in real-time new signal processing strategies for cochlear implants. Software development can be done either in C or in LabVIEW. The C implementation can be further optimized using Intels primitive routines. In this paper, we report on the real-time implementation of a 16-channel noise-band vocoder algorithm, which is a similar algorithm used in commercially available implant processors. We further report on EEG recordings on the PDA acquired through a compact-flash data acquisition card.

Real-time implementation of wavelet-based Advanced Combination Encoder on PDA platforms for cochlear implant studies

This paper presents the real-time implementation of wavelet-based Advanced Combination Encoder on PDA platforms for cochlear implant studies. Three real-time implementations using the conventional FFT, our previous recursive DFT, and the wavelet transform are compared in terms of computational complexity, processing time and fixed-point accuracy. The results obtained show that this new real-time implementation on PDA platforms is computationally comparable to our previous real-time recursive DFT implementation while achieving a higher accuracy or a lower quantization error.

Real-time PDA-based recursive Fourier transform Implementation for cochlear implant applications

This paper presents a real-time and interactive implementation of the recursive Fourier transform approach on PDA platforms for cochlear implant signal processing applications. PDA platforms provide a cost-effective and portable platform for cochlear implant studies. The computational complexities of the two commonly used signal processing strategies that are being used in commercial cochlear implants are compared. A more computationally efficient approach using recursive Fourier transform is discussed and a real-time implementation of this approach is then accomplished on a PDA platform. Different versions of the implementation are examined and compared in terms of speed and accuracy.

Cochlear Implantation Updates: The Dallas Cochlear Implant Program

This report provides an overview of many research projects conducted by the Dallas Cochlear Implant Program, a joint enterprise between the University of Texas at Dallas, the University of Texas Southwestern Medical Center, and Childrens Medical Center. The studies extend our knowledge of factors influencing communication outcomes in users of cochlear implants. Multiple designs and statistical techniques are used in the studies described including both cross sectional and longitudinal analyses. Sample sizes vary across the studies, and many of the samples represent large populations of children from North America. Multiple statistical techniques are used by the team to analyze outcomes. The team has provided critical information regarding electrode placement, signal processing, and communication outcomes in users of cochlear implants.

An Event-Related Potential Study of Older Children With an Early History of Failure to Thrive

Elementary and junior high school children (n = 13), who were diagnosed with nonorganic failure to thrive (FTT) as infants and toddlers, were compared with a normal control group (n = 14) on visual event-related potentials (ERPs) elicited during a primed lexical decision task. Positive stimuli were real words that were identical to the priming stimuli; negative stimuli were nonpronounceable letter strings. Although the groups did not differ in word-list reading level, the former FTT group had slower reaction (decision) times and did not show ERP evidence of priming in the N400 epoch. Anterior sites yielded better separation of the real words and letter strings than posterior sites. A late anterior component between 500 msec to 650 msec poststimulus onset showed the largest condition effect for both groups. The control group had a larger negative going late anterior component to words than the FTT group. The combined reaction time and ERP findings point to less automatized word recognition in the FTT group.

On the use of Bayesian modeling for predicting noise reduction performance

In speech enhancement applications, a validated metric of noise reduction performance is vital in the relative ranking of noise reduction algorithms and in enhancing the performance of a noise reduction algorithm. Subjective scores of enhanced speech remain the yardstick for performance, but objective metrics that emulate subjective evaluations are preferred for cost- and time-effectiveness. In this paper, we analyze the performance of two objective methods for predicting the quality of enhanced speech. The first method employs the coherence-based speech intelligibility index, while the second method uses features derived from the Moore - Glasberg auditory model. In both cases, the features are mapped to a quality score using the Bayesian modeling approach. Results show that the combination of the auditory model-based feature set and the Bayesian modeling provides the best performance in predicting the quality scores of enhanced speech.

An interactive hybrid programming approach to signals and systems laboratory

Signals and systems lab courses that are currently offered at many universities are mostly based on text-based programming languages and environments, in particular MATLAB. This paper presents an alternative programming approach in these courses by combining textual with graphical programming. This hybrid programming approach offers code interactivity in a time-efficient manner. Example labs are presented to demonstrate how this approach allows students to interact and experiment with their codes to gain a better understanding of the signal processing concepts.

Fetuses and neonates have different heart rate responses to low-intensity stimulation in quiet sleep

Abstract A sustained heart rate (HR) deceleration, elicited by low-intensity stimulation, is considered part of Sokolov’s generalized orienting reflex and is a useful measure of information processing in nonverbal subjects. This study was undertaken to investigate developmental changes in the perinatal period in information processing during quiet sleep (QS). Twenty-six infants were tested as fetuses at 36–40 weeks and again as neonates at a postnatal age of 2 weeks. Quiet sleep was defined in the same way for fetuses and neonates, and the same airborne sound was used for fetal and neonatal testing. We found that stimulation elicited a sustained, monophasic HR deceleration in the majority of fetuses. However, the response was more heterogenous when these infants were tested after birth, with approximately half the 2-week-old infants exhibiting a prolonged HR deceleration and half exhibiting a HR acceleration. These data provide evidence that a developmental change may occur, between the prenatal and postnatal periods, in information processing during QS.

Amplification and training effects in resolution and cross‐spectral integration of redundant cues

Speech recognition of hearing‐aid and cochlear‐implant users is constrained partly by inefficient integration of information conveyed by multiple frequency channels: owing to cross‐channel interference, multi‐channel recognition accuracy is often lower than the sum of single‐channel accuracies, especially if one channel has impaired sensitivity. With complex tones consisting of a mid‐ (M) and a high‐frequency (H) component (1000 and 3127 Hz), the resolution and cross‐spectral integration (CSI) of simultaneous increments in M frequency (IFM) and H duration (ITH) were studied as a function of H amplification and training; M and H impinged, respectively, on normal‐ and impaired‐sensitivity regions of listeners with sensorineural losses. Without amplification, ITH resolution was negligible, the IFM discrimination threshold did not decrease with ITH, and CSI was nil. With H amplification, resolution improved moderately for ITH but decreased for IFM; that is, increasing H audibility interfered with IFM resoluti...