Biomedical subjects

H G McAllister

Publications and source records attributed to H G McAllister.

6 recordsLinked to original sources

PubMed2001

Perceptual time-frequency subtraction algorithm for noise reduction in hearing aids.

Sensorineural hearing disorders are a major and universal community health problem. In many cases, hearing aids offer the only solution for people suffering from such disorders. Unfortunately existing aids do not provide any improvement in intelligibility of the signal when background noise is present. A hearing aid system should ideally simulate auditory processes including those aspects of the speech signal that are perceptually important. This work presents a new integrated approach to the design of a digital hearing aid, based on a wavelet transform, as well as a formulation of the temporal and spectral psychoacoustic model of masking. Within the model, the Perceptual Time-Frequency Subtraction (PTFS) algorithm is developed to simulate the masking phenomena and reduce noise in single-input systems. Results show that the use of the PTFS yields a significant improvement in speech quality especially in unvoiced portions. Additionally, the noise component during periods of silence has been attenuated by up to 20 dB. This new noise reduction method is expected to be applicable in a variety of applications, including digital hearing aids and portable communication systems (e.g., cellular telephones).

Algorithms↗

PubMed2001

Paradigms for recording cognitive brain electrical activity.

Human event-related potentials reflect cognitive processing, and are normally elicited by external events, such as acoustic sounds or visual stimuli. As such they provide an opportunity to study normal and abnormal brain function noninvasively, at sub-second resolution. Advances in multimedia technology permit specialists in informatics and neuropsychology to co-operate in the design and implementation of paradigms, which influence ERP components. The paper illustrates the progression from standard paradigms such as the auditory oddball, which can be used to study memory update through to contingent negative variation and three condition, visual paradigms which can be used to study cognitive and emotional responses. Data from a study investigating the comparative processing of target pictures and words illustrate how external stimuli influence the later cognitive potentials.

Brain Mapping↗

PubMed1999

Multimedia stimulation for psychophysiological investigation.

This paper describes a multimedia approach to sensory stimulation in psychophysiological studies. High resolution colour images are presented to a subject by a Delphi stimulus program, controlled by a data acquisition system which concurrently records cognitive Event Related Potentials from the subject. The acquisition PC is linked to the stimulus PC using serial communications and requests slide material using a character based protocol. The sound card in the data acquisition system can present concurrent complex auditory stimuli for multimedia experiments.

Acoustic Stimulation↗

PubMed1994

PC software library for the production of auditory stimuli in cognitive event-related potential experiments.

Software which provides an interface to the features of the Sound Blaster Pro card for the IBM PC using MS-DOS is described. The library may be called from a Turbo Pascal version 6 program. It permits tones of specified frequency (500 Hz-8 kHz in increments of 500Hz) and aversive noise to be turned on and off by a controlling program, during cognitive event-related potential paradigms. Tones are synthesized by hardware and noise is replayed from memory using the digital sound processor. The library provides the appropriate level of abstraction for the programmer designing such paradigms, by hiding the detail of the register level. It provides a model for programming the card in other high level languages and may be augmented to provide more complex stimuli, such as short segments of speech or music. The card when controlled by the library provides a versatile and cost effective alternative to an audiometer in the electrophysiological laboratory.

Cognition↗

PubMed1983

Data acquisition in neurophysiology. A flexible microcomputer system for recording neurophysiological data.

The advent of the microprocessor, and its incorporation in relatively low-cost microcomputer systems, offers a new range of possibilities for the recording of evoked and event-related potentials. A flexible system for recording evoked potentials, entitled DAN, has been developed using an Apple microcomputer. The main objective in developing DAN was to make it sufficiently flexible so that it could be used in both a research and a clinical environment for a wide range of responses, from the auditory brainstem to much slower cortical responses. A specific response can be selected from a standard range of evoked responses, or if a non-standard response is required, it is a simple matter to specify the response stimulus parameters, time duration and data sampling rate. This degree of versatility is achieved by designing a programmable audiometer, a special-purpose hardware interface for the Apple and software to generate the stimulus and control the data-acquisition interface. The main hardware components of the DAN system are listed (a) Apple microcomputer operating under U.C.S.D. PASCAL operating system; (b) dual 5 1/4 inch floppy disk drives and controller; (c) Video monitor; (d) DAN data-acquisition interface; (3) programmable audiometer; (f) Epson MX-80 printer/plotter. Disk drive 1 of the dual drive set is used to store the PASCAL operating system and the DAN programs. Drive 2 is used to store the data. The data-acquisition interface and audiometer interface plug into slots in the Apple. The software includes routines to generate the stimulus and store it in the audiometer prior to the data-acquisition phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Computers↗

PubMedDate not supplied

Computer-assisted measurement of peripheral blood flow.

An automated system for the measurement of peripheral blood flow using venous occlusion plethysmography based on the low-cost Apple II microcomputer, together with purpose-built compressor unit and data acquisition interface, has been developed. The computer performs the dual role of controlling the timing of inflation and deflation of the occluding cuffs and recording the resulting increase in limb circumference. Ten 8 s epochs of data are acquired and analysed per session. Flow rate is computed using a least squares fit between 0.5 and 4.0 s after cuff inflation, giving on-line indication of blood flow. Venous capacitance and digital systolic pressure may be measured using additional algorithms. The system has been used for the investigation of circulatory disorders and in the assessment of drugs acting on the peripheral circulation.

Blood Pressure↗